Risk Factors for Increased Airway Responsiveness to Methacholine Challenge among Laboratory Animal Workers 1- 3
CAROL A. NEWILL, VALERIE L. PRENGER, JAMES E. FISH, RICHARD EVANS III, EARL L. DIAMOND, QINGYI WEI, and PEYTON A. EGGLESTON
A
Introduction
number of cross-sectional studies have examined the prevalence of airway hyperreactivity and the risk factors for this abnormality (1-9), but to date few have focused on the working age range 18to 55 yr (1,8,9). As part of a prospective study of the incidence of allergic asthma, we evaluated a large group of workers entering employment that involves exposure to laboratory animal allergens. This report presents cross-sectional data on potential risk factors for bronchial hyperreactivity among healthy young adults in this occupational setting. It specifically addresses the hypotheses that prior work experience and atopic status are risk factors for sensitization and disease. Methods Ascertainment of Subjects and Study Design Volunteers were research personnel (faculty, fellows, students, technicians) exposed to laboratory animals in their work in a medical research center. They were excluded if they had a history of symptomatic asthma with animal exposure, but they were not excluded if they had other allergic symptoms (e.g., rhinitis, conjunctivitis, rash). Symptomatic asthma was defined as the presence of at least three of the following symptoms: wheezing, breathlessness, chest tightness, or productive cough associated with workplace exposure. They were not excluded if they had these symptoms but could not relate them to the workplace. At enrollment in the study, volunteers underwent spirometry, methacholine challenge testing, allergen skin testing, and personal interviews. Potential study subjects were ascertained systematically through an extensive"Contact Network" made up of keypersons in each laboratory in which exposure to laboratory animals occurred, as well as the staff of the Occupational Health Office. Every 3 or 4 months, members of the Contact Network identified any persons newlyadded to the staff as well as any positions that were anticipated to be filled in the next year. In addition, current volunteers were asked to assist in the 1494
SUMMARY As a first step in a prospective stUdy of the Incidence of asthma to laboratory animals, a group of 364 adults 18 to 48 yr of age who were beginning employment with laboratory animals were evaluated In terms of their past history, health status, allergy, and airway responsiveness to methacholine. At entry to the stUdy, 269 had previous occupational contact with animals, 109 had chest symptoms In the previous year, 168 had a history of allergic symptoms to laboratory animals (any with asthmatic responses were systematically excluded), and 118had positive Immediate skin tests (29 had positive skin tests to laboratory animals). When defined as a PD,.FEV, of 80 breath units or less, 18.4% of these young adults had methacholine hyperresponslveness (HRA). Significant risk factors for HRA were found to be younger age, female sex, lower educational level, a history of allergic symptoms to laboratory animals, and a history of chest symptoms. Positive skin tests to laboratory animals were present in 8% of workers; this was not a significant risk factor for HRA although positive skin tests to pollen and household allergens were. PreviOUS work experience was a risk factor, especially among those with allergic symptoms, and a trend toward self-selection was suggested In that the rate of HRA was lowest In workers with more than 2 yr of experience or With AM REV RESPIR DIS 1992; 146:1494-1500 two or more previous jobs with laboratory animals.
ascertainment and recruitment of eligiblecolleagues. Potential subjects were recruited vigorously.
Pulmonary Function Testing Spirometry was performed according to ATS guidelines (10) using a rolling-seal spirometer (Model 822; Ohio Medical Products, Houston, TX). A technicallyacceptable spirogram met the following requirements: at least a 6-s duration, or 4 s if no change in the slope of the tracing; no cough in the first second; no cough affecting accurate measurements of the FVC; back-extrapolated volume less than 10070 of measured FVC. Measurements were corrected for BTPS. The best FEV, value of three satisfactory efforts was recorded and compared with predicted norms (11). Volunteers with FEV, 80070 or more of predicted proceeded to methacholine challenge testing. Methacholine challenges were performed according to a modification of the method of Chai and coworkers (12)and Fish and Kelly (13). Methacholine chloride (J. T. Baker Chemical Co., Phillipsburg, NJ) was prepared in 0.4% phenolated phosphate-buffered saline (PBS) (Hollister-Steir Laboratories, Spokane, WA) in concentrations of 1, 3, 10, and 25 mg/ml; for tests of subjects known to be highly reactive to methacholine, 0.25 and 0.5 mg/ml concentrations were prepared by onsite dilution. Aerosols were generated by a Model 646 nebulizer (DeVilbissCo., Somerset, PAl through a Rosenthal-French dosemetering device. Bronchodilators wereexclud-
ed for 24 h before the challenge. Volunteers inhaled five breaths of PBS, and FEV, was measured again. If this control value did not decrease by 10% or more, incremental concentrations of methacholine wereinhaled until FEV, decreased by 20% or more from control or until the 25-mg/ml solution was given. The dose causing a 20% fall in FEV, was interpolated from points on a log-linear dose-response plot and was designated the PD 2oFEV,_ This dose was expressed in breath units, where one breath unit (BU) is the equivalent of one inhalation of 1 mg/ml methacholine. (Received in original form June 26, 1991 and in revised form July 13, 1992) , From the Department of Immunology and Infectious Diseases and the Department of Epidemiology, The Johns Hopkins University School of Hygiene and Public Health, and the Department of Pediatrics, The Johns Hopkins UniversitySchool of Medicine,Baltimore, Maryland, the Department of Medicine, Jefferson Medical College, Philadelphia, Pennsylvania, and the Department of Pediatrics, Northwestern University School of Medicine, Chicago, Illinois. 2 Supported by Grant HL-30532 from the National Institutes of Health and by the Eudowood Fund of the Hospital for Consumptives of Maryland. 3 Correspondence and requests for reprints should be addressed to Peyton A. Eggleston, M.D., Department of Pediatrics, The Johns Hopkins Hospital, 600 North WolfeStreet, Baltimore,MD 21205.
1495
BRONCHIAL REACTIVITY IN LABORATORY ANIMAL WORKERS
Interview and Skin Jests Extensive, standardized, personal interviews, including questions regarding symptoms of allergy and asthma, wereadministered. Symptoms of asthma recorded were: intermittent episodes of wheezing, breathlessness (defined as episodes or attacks of difficulty in breathing, shortness of breath, or ability to take a deep breath), chest tightness (feeling of tightness or heaviness in the chest, possibly extending upward into the throat) and productive cough with sputum or phlegm (for at least 3 consecutive weeks). Immediate wheal and flare skin tests were performed by the prick-puncture technique of Santilli and coworkers (14). Materials included glycerinated extracts (1:20 wt:vol;Greer Laboratories, Lenoir, NC) of house dust, Alternaria, Aspergillus, short ragweed pollen, orchard grass pollen, and rat, mouse, guinea pig, and rabbit epithelium. Histamine phosphate 0.5 mg/ml was used as a positive control, and 500/0 glycerinated PBS (Hollister Steir) was used as a negative control. Tests applied in duplicate on the flexor surface of both forearms were read at 15 to 20 min. A positive test was defined as having at least one wheal ~ 4 mm in diameter, with the smaller wheal diameter ~ 2 mm. A valid skin test was defined as one in which the average wheal diameter of the two glycerine control tests was ~ 2 mm and the average wheal diameter of the positive controls was ~ 4 mm. All subjects denied receiving oral or nasal medications containing antihistamines within 48 h. Subjects Included in Analyses The target population was the estimated 1,200 people in the Johns Hopkins University who work with or use animals in their research or training, including students, faculty, research staff, and animal caretakers. The turnover rate among the staff is about 15% annually, 27% biennially, so that about 180 people begin working with animals at this institution each year. The study enrolled 504 subjects from this group. An additional 141 eligiblesubjects were contacted, but they refused to join the study, and 33 others refused to disclose sufficient information for assessment of eligibility. Of the 504 volunteers, 140 were excluded from the analysis because spirograms in their methacholine challenge tests on their initial visit were not sustained for a full 4 s and thus were not technically acceptable. These 140 differed from the remaining 364 only in having a larger proportion of women and a lower proportion with a history of allergic symptoms (see table 1). The 364 study subjects were 18 to 48 yr of age at the time of their initial test (median age, 26). Forty-six percent were women. Only 52 of 364 (14%) were current smokers at the time of their initial test, and 73% had never smoked. Most (316 of 364; 87070) were college graduates, and almost 50% (181 of 364)worked as research technicians. Although
TABLE 1 CHARACTERISTICS OF STUDY POPULATION WITH AND WITHOUT ACCEPTABLE METHACHOLINE CHALLENGE TESTS Acceptable Challenges (n 365)
=
Challenges not Acceptable(n 140)
=
(n)
(%)
(n)
(%)
P Value
119 245
32.7 67.3
46 94
32.9 67.1
0.972
166 198
45.6 54.4
80 60
57.1 42.9
0.020
52 45 267
14.3 12.4 73.3
22 15 103
15.7 10.7 73.6
48 163 153
13.2 44.8 42.0
28 50 62
20.0 35.7 44.3
0.024 0.194
181 183
49.7 52.3
58 82
41.4 58.6
0.095
279 55 30
76.6 15.2 8.2
109 21 10
77.9 15.0 7.1
0.888 0.801
95 159 110
26.0
43.7 30.3
39 59 42
27.9 42.1 30.0
168 196
46.2 53.8
41 99
29.3 70.7
0.001
109 255
29.9 70.1
52 88
37.1 62.9
0.121
Age, yr
18-23 24-48 Sex Female Male Smoking Current Past Never Educational level Below bachelors Bachelors Above bachelors Current job group Handler, tech Others Years in current job
2 Previous jobs with lab animals None
1 ;"2 History of allergy to lab animals t Yes No Chest symptoms; Yes No
ref
ref
ref 0.543
0.741 ref
ref
ref
ref 0.678
0.783 ref
ref
• Methacholine challenges were considered unacceptable when one or more spirograms were performed with an effort that was not sustainedfor 4 s or more. t Presence of allergicsymptoms (rhinitis, conjunctivitis, rashes) that could be relatedto exposureto a laboratoryanimal. :j: Historyof intermittentbreathlessness. Wheezing, chest tightness,or productivecough in the year prior to entry into the study.
most (269 of 364; 74%) had worked with animals in previous jobs, the majority (279 of 364) had worked in the present job for a year or less. Forty-six percent reported rhinitis, conjunctivitis, and/or skin rash on exposure to at least one species of laboratory animals; 109 (30%) had at least one chest symptom in the year prior to testing, but they could not relate these symptoms to animal exposure.
Analytic Methods Cross-sectional analysis of the frequency of airway hyperreactivity and its association with clinical, demographic, and occupational factors was performed using the SAS system (15) to perform chi-square tests, odds ratios and confidence intervals on odds ratios, and to calculate the probability that odds ratios differed from unity (16, 17). Results are presented in terms of both cross-sectional frequencies as well as the appropriate summary statistic, the odds ratio. Adjustment for age,
sex, and chest symptoms was carried out by logistic regression (18). Results
Frequency Distributions of Degree of Responsiveness As seen in figure 1, 67 volunteers (18.40/0) reacted to methacholine challenge with a PD2 0FEV 1 in the asthmatic range ~ 80 BU (19), and 18 (4.9%) were in the moderate to severe range (~ 20 BU). Risk Factors Associated with Hyperreactivity The proportion of subjects with HRA among those with and without risk factors at the time of enrollment in the study is shown in table 2. Being younger or female and having a lower educational level were significant risk factors for HRA. Tobacco smoking was not. Most subjects
1496
NEWILL, PRENGER, FISH, EVANS, DIAMOND, Wet, AND EGGLESTON
80 260
n=364
70 -"
60
i"
~
SO
u.
o rZ W
40 30
U
1 pack per day; these findings were similar among ex-smokers, of whom 64.4% reported ~ 1 pack per day and 6.6% > 1 pack per day. On-the-job experience with laboratory animals showed some trends with HRA. There was little difference in the frequency of HRA in workers employed as laboratory technicians or as animal handlers (29 of 181, 16%) when compared with faculty, students, postdoctorates, or administrators (38 of 183, 21%). However, the most experienced workers tended to have the lowest rates of HRA. For example, among the small number employed for more than 2 yr in their current job, only three of 30 (10%) had HRA compared with 17.6% of those in their first year and 27.3% ofthose in their second year of employment. The likelihood of having HRA was significantly greater among workers employed 1 to 2 yr relative to more experienced workers (odds ratio, 3.38; p = 0.036). A similar trend was seen among the 110 subjects who had held two or more previous jobs with laboratory animal exposure, of whom 15.4% had HRA compared with 23% of those with no previous job; how-
TABLE 2 RELATIONSHIP OF DEMOGRAPHIC AND OCCUPATIONAL CHARACTERISTICS AND ALLERGY HISTORY TO AIRWAY HYPERREACTIVITY (HRA) HRA Positive' Risk Factor at Entry
Odds Ratio
95% CI
P Value
26.9 14.2
2.21
1.40-3.47
0.002
42 25
25.3 12.6
2.34
1.48-3.71
0.001
48 163 153
12 34 21
25.0 20.9 13.7
2.10 1.66
1.07-4.10 1.04-2.83
0.035 0.049
52 45 267
12 5 50
23.8 11.1 18.7
1.30 0.54
0.71-2.37 0.24-1.23
0.235 0.110
181 183
29 38
16.0 20.8
0.90
0.68-5.39
0.351
279 55 30
49 15 3
17.6 27.3 10.0
1.92 3.38
0.68-5.39 1.10-10.30
0.150 0.036
95 159 110
22 28 17
23.2 17.6 15.4
1.65 1.17
0.91-2.97 0.67-2.03
0.082 0.321
168 196
38 29
22.6 14.8
1.68
1.07-2.64
0.028
Number
(n)
(%)
364
67
18.4
119 245
32 35
166 198
Total group Age group, yr
18-23 24-48 Sex Female Male Education level Below bachelors Bachelors Above bachelors Smoking Current Past Never Current job group Handler, tech Others Years in current job
.. 1 > 1 to 2 >2 Previous jobs with lab animals None
1 ;;.2 History of allergy to lab animals t Yes No
ref
ref
ref
ref
ref
ref
ref
ref
• Defined as PD"FEV, .. 80 breath units.
t Defined as rhinitis, conjunctivitis, and/or rash with exposure to any animal(s) in the workplace.
ever, this comparison did not reach statistical significance (odds ratio, 1.65; p = 0.082). That these trends toward the lowest cross-sectional frequency of HRA were found among the workers with the most previous laboratory animal job experience suggests that those with HRA had left the work force in greater numbers before entering this study. A positive history of allergy to animal(s) in the workplace (defined as complaints of rhinitis, conjunctivitis, and/or rash) was associated with HRA, as 23% of 168 subjects with symptoms had HRA compared with 15% of 196 denying such symptoms (p = 0.028). The relationship between experience in the workplace and HRA was seen most strongly among the 168 subjects with a history of allergic symptoms to laboratory animals, as shown in table 3. For example, among the 32 subjects who had held no previous jobs working with laboratory animals (i.e., were in their first such job), 38% had HRA compared with 14% of those 65 who had held two or more jobs (odds ratio, 3.73; p = 0.009). The association between workplace experience and HRA was much weaker among the 196 subjects who denied a history of allergy to laboratory animals. As shown in table 3, the corresponding odds ratio was only 0.87 (p = 0.70). A similar trend was seen when the frequency of HRA was related to workers' length of experience in their current job. These trends suggest that workers with a history of allergic symptoms and HRA, i.e., those most likelyto havechest symptoms, were less apt to continue working with animals or to take another job with animal exposure. As seen in table 4, the presence of a positive skin test was associated with more frequent HRA. Of 355 volunteers who had valid skin tests to inhalant allergens, 118 had a positive response to any allergen. Only 29 (8%) had positive skin tests to any of four common laboratory animal allergens, even though nearly half of the workers reported allergic symptoms associated with laboratory animal exposure. Seventy-sevenvolunteers (22%) had positive skin tests to household allergens, including 31 with positive reactions to cat and/or dog allergens. A positive skin test to cat or dog allergen was associated with a positive skin test to laboratory animal allergens (rat, rabbit, mouse, and/or guinea pig); of the 31 subjects who reacted to cat and/or dog allergens, eight (36%) also reacted to laboratory animal allergens,
BRONCHIAL REACTIVITY IN LABORATORY ANIMAL WORKERS
1497
TABLE 3
reporting any two or more symptoms (odds ratio, 4.63; p < 0.0001). Among the demographic characteristics of the participants, the two most strongly associated with HRA (younger age and female) could in turn influence other variables such as smoking, time on the job, education, and job title (i.e., younger subjects and women tended to have attained less education) and their relationship to HRA. Therefore, logistic regression analyses were carried to adjust for the effect of each of these two variables. The relationships between the other risk factors and HRA after adjustment for age and sexseparatelyare shown in table 6. For instance, the association with educational background, whereby in workers with less education there was a greater number with HRA, disappeared when adjusted for age or sex.The association between positive skin tests to pollen allergens and HRA was strengthened somewhat when adjusted for sex (odds ratio 2.64; p = 0.0008); this related to a much higher frequency of positive skin tests among men (520/0 versus 28%). The relationship between HRA and several risk factors, notably, history of allergy to laboratory animals, the presence of two or more chest symptoms, and skin test sensitivity to pollens or to laboratoryanimals, wasnot altered by adjustment for age or sex. Also shown in table 6 are the results of reanalyzing the risk factors with adj ustment for the presence of chest symptoms. This was done both because the presence of chest symptoms was such a strong risk factor for HRA and because the presence of chest symptoms might influence work behavior or the relationship of allergy and HRA. This adjustment diminished the association between time in the current job and HRA, i.e., the odds ratio for 1 to 2 yr previous experience compared with more than 2 yr decreased from 3.38 to 3.06 and was no longer significant. When adjusted for chest symptoms, the effect of allergy to laboratory animals, either as indicated by history or by skin test sensitivity to animal allergens, was diminished as well.
INTERRELATIONSHIP OF PAST HISTORY OF ALLERGIC SYMPTOMS ASSOCIATED WITH LABORATORY ANIMALS TO LABORATORY ANIMAL EXPOSURE HISTORY AND TO AIRWAY HYPERREACTIVITY (HRA) HRA Positive'
(Ok)
Odds Ratio
95% CI
p Value
25 12 1
21 38 7
3.65 8.40
0.56-160 0.98-384
0.172 0.027
12 17 65 9 No history of allergy to laboratory animals, n = 196
38 24 14
3.73 1.96
1.21-11.7 0.75-5.42
0.009 0.100
0.24-11.3 0.10-13.2
0.602 0.702
0.28-2.81 0.22-2.07
0.702 0.861
Number
(n)
Positive history of allergy to laboratory animals, n Years in current job
2 Previous jobs with lab animals None
32 71
1 ;'2
ref
ref
Years in current job
2
158 23 15
24 3 2
15 13 13
1.16 0.98
63 88 45
10 11 8
16 13 18
0.87 0.66
Previous jobs with lab animals None
1 ;'2
ref
ref
, Defined as PD"FEV, " 80 breath units. Defined as rhinitis, conjunctivitis, and/or rash with exposure to any animal(s) in the workplace.
t
compared with only 21 of 324 (6%) who did not react to cat or dog allergen (chi square, 14.1; p = 0.0001). Although skin test reactivity to pollens and laboratory animals appeared to be related to each other (odds ratio, 7.17; p < 0.0001), cross tabulation of the two categories of allergens in table 4 showed that only pollen skin test reactivity, and not laboratory animal allergen reactivity, was associated with HRA cross-sectionally.
Not surprisingly, in the subjects who in their initial interview reported having two or more chest symptoms to any trigger during the year before enrollment in the study there was a significantly greater number with HRA than in those subjects who denied such symptoms (see table 5). Breathlessness was the single symptom most strongly associated (odds ratio, 4.12; p < 0.0001), but HRA was detected in almost half (20 of 45) of those
TABLE 4 RELATIONSHIP OF SKIN TESTING RESULTS TO HRA HRA Positive' Number Valid skin test t Laboratory animals:!: Positive Negative Pollans§ Positive Nagative Perennial household allergensll Positive' Negative Skin test to animals and/or pollen allergens + animall + pollen + animal/- pollen - animal! + pollen - animal/- pollen
Odds Ratio
95% CI
p Value
31.0 17.2
2.17
0.82-5.29
0.061
31 34
27.7 14.0
2.35
1.30-4.22
0.002
77 278
29 36
37.7 13.0
4.06
23 6 89 237
7 2 24 32
30.4 33.3 27.0 13.5
2.80 3.20 2.37
(n)
(Ok)
355
65
18.3
29 326
9 56
112 243
raf
ret 2.17~7.52
< 0.0001
0.90-7.87 0.28-23.3 1.23-4.47
0.039 0.199 0.004
raf
Discussion
ref
• Defined as PD"FEV, " 80 breath units.
t Mean glycerine wheal" 2 mm, mean histamine wheal .. 4 mm.
*Rat, rabbit, mouse, and/or guinea pig.
§ Grass and/or ragweed. II Dust, Alternaria, cat, and/or dog. , Larger wheal .. 4 mm in diameter, smaller wheal" 2 mm In diameter. or, if only one arm tested, than" 4 mm.
This report shows that the frequency of HRA, as defined by methacholine PD zoFEVl ~ 80 BU, was 18.4% in this group of young adult laboratory workers. This figure is similar to prevalence rates in other series of adults and children, which have ranged from 17.9% (3) to 28% (2). The frequency seen with any
1498
NEWILL, PRENGER, FISH, EVANS, DIAMOND, WEI, AND EGGLESTON
TABLE 5 RELATIONSHIP OF CHEST SYMPTOMS IN THE LAST YEAR TO HRA HRA'
Breathlessness Yes No Wheezing Yes No Chest tightness Yes No Productive cough Yes No Any of four symptoms Yes No Two or more symptoms Yes No
Number
(n)
(%)
Odds Ratio
95% Cl
P Value
45 319
19 48
42.2 15.1
4.12
2.36-7.22
< 0.0001
52 312
16 51
30.8 16.4
2.35
1.35-4.10
0.006
47 317
16 51
34.0 16.1
2.69
1.40-4.74
0.002
28 336
8 59
28.6 16.1
1.88
0.91-3.89
0.077
109 255
29 38
26.6 14.9
2.07
1.31-3.28
0.005
45 319
20 47
44.4 14.7
4.63
2.65-8.09
< 0.0001
ref
ref
ref
ref
ref
ref
, Defined as PD"FEV, .. 80 breath units.
test for airway reactivity obviously depends on the criteria for a positive response (19). Our definition is based on the work of others, which has shown that greater than 95% of current asthmatics (9) and only 3010 of a population selected to exclude asthmatics (20) will have an abnormal response. Our population was similar to others, and it was unselected except that recruitment was based on anticipated exposure to laboratory animals and that workers with a history of asthma on exposure to laboratory animals wereexcluded. The latter requirement was required by the overall design to study prospectively the development of clinically significant asthma reaction to animals in the workplace over a period of time. The association of HRA with younger age and with the female sex in this
TABLE 6 ADJUSTED RISK FACTORS FOR HRA HRA Positive' Risk Factor at Entry Total group Age group, yr
18-23 24-48 Sex Female Male Education level Below bachelors Bachelors Above bachelors Smoking Current Past Never Current job group Handler, tech Others Years in current job
1 to 2 >2 Previous jobs with lab animals None
1 ;'2 History of allergy to laboratory animals Yes No Two or more chest symptoms in past year Yes No Positive skin tests to pollen allergensII Yes No Positive skin tests to animal allergens Yes No
Sex-adjusted
Age-adjusted
Number
(n)
(%)
364
67
18.0
119 245
32 35
26.9 14.2
166 198
42 25
25.3 12.6
2.29
48 163 153
12 34 21
25.0 20.9 13.7
1.23
52 45 267
12 5 50
23.8 11.1 18.7
1.49 0.67
181 183
29 38
16.0 20.8
0.63
279 55 30
49 15 3
17.6 27.3 10.0
1.55 2.82
95 159 110
22 28 17
23.2 17.6 15.4
1.26 0.96
168 196
38 29
22.6 14.8
1.58
45 319
20 47
44.4 14.7
4.52
112 243
31 34
27.7 14.0
2.32
29 326
9 56
31.0 17.2
2.42
Odds Ratiot
p Value
Odds Ratio
p Value
Odds Ratio*
p Value
2.15
0.003
2.14
0.008
2.24
0.002
*
0.004
ref
ref
0.30
ref §
1.77 1.33
0.08 0.19
0.14 0.21
ref
0.051
ref
§
1.06 0.55
ref
ref
1.29
0.58
0.24
0.03
1.71 3.23
0.19 0.04
0.26 0.45
1.81 1.25
0.05 0.06
0.05
1.68
0.03
< 0.0001
4.43
1.77 3.06
0.35 0.10
1.56 1.17
0.23 0.65
1.48
0.16
ref
ref
ref
0.09
ref
ref
ref
0.62
0.88 0.22
ref
ref
ref
0.20 0.009
ref
ref
0.24 0.07
1.76 1.67 ref
ref
< 0.0001
ref
ref
0.003
2.64
0.0008
0.053
2.42 ref
2.30
0.005
ref
ref
ref
, Defined as PD"FEV, .. 80 breath units. Odds ratios were adjusted on age groups 18 to 23 yr (n = 119)and 24 to 48 yr (n = 245). Presence of two or more chest symptoms in past year (wheezing, breathlessness, chest tightness, productive cough). § Cell size did not allow valid calculation of odds ratio. II Positiveskin test = larger wheal", 4 mm in diameter, smallerwheat", 2 mm in diameter, or, if only one arm tested, then", 4 mm.
t
ref
ref
ref
Symptom-adjusted
0.054
1.94 ref
0.20
BRONCHIAL REACTIVITY IN LABORATORY ANIMAL WORKERS
study was unexpected and cannot be explained easily. Age-dependent variations among adults have been addressed in only a few other studies; older age has been associated with greater degree of reactivity to methacholine among men, most of whom had occupational exposure to air contaminants associated with increased risk of asthma (8), whereas in a series of asymptomatic, nonsmoking men and women, no difference was seen with age (20). However, separate reports of HRA in adults and in children would suggest that the prevalence is higher among children and young adults (4,5). In our data, the age difference was related in part to job experience, as older workers tended to have been employed in their current job longer and to have had more previous jobs with laboratory animal exposure. Probably because of the healthy worker effect, these workers tended to have been self-selected for lack of airway hyperreactivity or its associated symptoms. Given the higher prevalence of symptomatic asthma in men (21), it was surprising to find a higher frequency of HRA among women in our study. Two other studies have addressed sex as a risk factor for HRA (5, 7) and found no difference; however, Malo and colleagues (20) did find a small but significantly higher rate among women in a series of asymptomatic, nonsmoking normal volunteers. We evaluated several possible explanations for the association. For instance in our series, it is possible that women and subjects with less education may have been more likely to have jobs that would expose them to higher concentrations of animal allergens (22), or they may have had less mobility in their jobs. Indeed, when educational level was examined as a risk factor with adjustment for sex, the association with HRA was diluted, indicating an interaction between sex and educational level and risk of HRA. This suggests that the sex difference in HRA may have an environmental basis. Two risk factors that we found associated with HRA were those identified in previous population studies, i.e., positive allergy skin tests (23) and a history of chest symptoms (2). A history of asthma symptoms in the year prior to enrollment in the study was found to be associated with more than a 4-fold increased risk of HRA. However, the personal interview reporting of asthma symptoms was not highly predictive of HRA, as only 44OJo of those with ahistory of two or more recent symptoms had
demonstrable HRA. On the other hand, only 15% of 319 subjects without such a history had HRA. Both of these figures are consistent with the findings of others. For instance, Asher and colleagues (4), using the same definition of HRA, found that 43% of children with current symptoms consistent with asthma had HRA compared with 11 % of those without symptoms. Dales and colleagues (6), using a modified American Thoracic Society questionnaire, found that a history of ever wheezing was associated with HRA, with a specificity of 87% in an occupational sample in which 21% had airway reactivity. Burney and Chinn (2), using the International Union Against Tuberculosis questionnaire, found that a history of wheezing in the previous year was associated with HRA, with a specificity of 72% in a sample enriched for history of wheezing; this corresponded to a frequency of HRA of 55% in subjects answering "yes" and 7% in those answering "no." Without a gold standard, it is difficult to determine which of the two instruments, the questionnaire or the bronchoprovocation, is more useful for categorizing our participants as asthmatic, but our data clearly support the conclusions of other investigators (2, 7) that airway reactivity bears only a loose relationship to asthmatic symptoms in a population. Skin test reactivity to pollen and common household allergens was associated with HRA. This is consistent with the observations of Burrows and colleagues (24) and O'Connor and coworkers (23) that positive skin tests are associated with an increased frequency of asthmatic respiratory symptoms (24) and of HRA (23). Indeed, the statistically significant odds ratio of 2.35 between pollen skin test reactivity and HRA seen in our study was remarkably similar to the odds ratios of 3.0 and 3.3 observed by Peat and colleagues (3) in two Australian towns. In contrast, evidence of IgE reactivity to laboratory animal allergens in skin tests was not significantly associated with increased risk of HRA. The differences between plant pollen and animal dander allergen include the biologic and physical characteristics of the particles that bear the allergenic constituents. Our published data (25) show that a large proportion of particles bearing rat allergen have aerodynamic equivalent diameters ~ 1.3 11m, a size that allows penetration of the peripheral airways and air spaces. Although comparable data on aerodynamic characteristics of pollen particles are not available, the reported characteristics of
1499
pollen grains suggest that their distribution in lung may differ (26). The possibility that there are as yet unidentified differences in host immunologic reactivity to plant versus animal allergens also merits study. However, a more likely explanation is that the pattern of exposure to pollens and to laboratory animals differs in that pollen exposure is seasonal and lifelong, whereas laboratory animal exposure may be continuous on a day-to-day basis, but it does not occur for as many years. In this study, only 30 of 364 had been employed in their current job for more than 2 yr at the time of enrollment, and only 110 of 364 had held two or more prior jobs that entailed exposure to laboratory animals. Thus, our subjects, in addition to limiting their exposure to a few hours a day, had generally been exposed to animal allergens for less than 2 yr, so that the relationship to animal allergens was just emerging. This explanation is supported by our finding that the prevalence of HRA in these workers (18.9%) was similar to that in other populations (2, 3). The trend seen between workers with more than 2 yr of job experience and declining risk of HRA suggests a selfselection bias, sometimes called the healthy worker effect. Workers developing HRA in the workplace may incur symptomatic reactions to animals, causing them to move to other jobs with less or no exposure to animals. This would result in a lower frequency of HRA among those who have been on the job longest or who have held the greatest number of jobs in this workplace. Our data suggest that such an effect may have occurred, and this is consistent with the work of Venables and colleagues (27) with regard to atopic status in a crosssectional study of laboratory animal workers in England. The possibility of a self-selection bias in our cross-sectional analysis supports the hypothesis that chronic occupational exposure to laboratory animal allergens may lead to generalized airway reactivity to nonspecific stimuli such as methacholine, and that such hyperactivity may precede the development of clinically diagnosed asthma to the original, precipitating allergen(s). Prospective analyses of the risk of developing clinically significant asthma among laboratory-animal-exposed workers with and without HRA will help to elucidate these relationships. These data have implications for the management oflaboratory animal aller-
1500
NEWILL, PRENGER, FISH, EVANS, DIAMOND, WEI, AND EGGLESTON
gy and asthma in the workplace. First, they suggest that at any point in time, many laboratory animal workers have airway symptoms, positive allergy skin tests, and methacholine sensitivity; the prevalence of these manifestations is similar to that in the general population. Thus, preemployment screening procedures are likelyto be neither efficient nor effective in selecting a work force with lower risk for laboratory animal asthma. On the other hand, experienced workers without disease do appear to be a more distinct group. After only 1 to 2 yr of job exposure, it would appear that some of the symptomatic workers have removed themselves from the workplace. This trend probably cannot be changed and appears to produce a work force that is less likely to become symptomatic on the job. If it is not possible to screen effectively for high risk workers, the most obvious and logical step in prevention is to limit exposure to the allergen. In addition to maintaining good ventilation in laboratories and vivaria, it is important to use appropriate allergen control devices during high risk activities such as surgery and cage cleaning (22, 28) and to insist on the more general use of protective clothing and masks. Acknowledgment The writers would like to thank Alice Rodman for her contributions to the data collection and management and Barbara Wheeler for her help in preparing the manuscript.
References 1. Lam S, Wong R, Yeung M. Nonspecific bronchial reactivity in occupational asthma. J Allergy Clin Immunol 1979; 63:28-34. 2. Burney P, Chinn S. Developing a new question-
naire for measuring the prevalence and distribution of asthma. Chest 1987; 91:79S-83S. 3. Peat JK, Britton WJ, Salome CM, Woolcock AJ. Bronchial hyperresponsiveness in two populations of Australian school children. III. Effect of exposure to environmental allergens. Clin Allergy 1987; 17:291-300. 4. Asher MI, Pattemore PK, Harrison AC, et af. International comparison of the prevalence of asthma symptoms and bronchial hyperresponsiveness. Am Rev Respir Dis 1988; 138:524-9. 5. WeissST,Tager IB, WeissJW, Munoz A, Speizer FE, Ingram RH. Airway responsiveness in a population sample of adults and children. Am Rev Respir Dis 1984; 129:898-902. 6. Dales RE, Ernst P, Hanley JA, Battista RN, Becklake MR. Prediction of airway reactivity from responses to a standardized respiratory symptom questionnaire. Am Rev Respir Dis 1987; 135:817-21. 7. Rijcken B, Shouten JP, Weiss ST, Meinesz AF, Vries KD, Van Der Lende R. The distribution of bronchial responsiveness to histamine in symptomatic and in asymptomatic subjects: a populationbased analysis of various indices of responsiveness. Am Rev Respir Dis 1989; 140:615-23. 8. Enarson DA, Vedal S, Schulzer M,Dybuncio A, Chari-yeung M. Asthma, asthmalike symptoms, chronic bronchitis, and the degree of bronchial hyperresponsiveness in epidemiologic surveys. Am Rev Respir Dis 1987; 136:613-7. 9. Cockcroft DW. Measurement of airway responsiveness to inhaled histamine or methacholine: method of continuous aerosol generation and tidal breathing inhalation. In: Hargreave FE, Woolcock AJ, eds. Airway responsiveness: measurement and interpretation. Mississauga, ant: Astra, 1985; 22-6. 10. Ferris BG. Epidemiology standardization project. Am Rev Respir Dis 1978; 118:55-89. 11. Morris JF, Koski A, Johnson Le. Spirometric standards for healthy non-smoking adults. Am Rev Respir Dis 1971; 103:57-67. 12. Chai H, Farr RS, Froehlich LA, et al. Standardization of bronchial inhalation challenge procedures. J Allergy Clin Immunol 1975; 546:323-7. 13. Fish JE, Kelly JE Measurements of responsiveness in bronchoprovocation testing. J Allergy Clin Immunol 1979; 64:592-6. 14. Santilli J, Potsus RL, Goodfriend L, Marsh DG. Skin reactivity to purified pollen allergens in highly ragweed sensitive individuals. J Allergy Clin
Immunol 1980; 65:406-14. 15. SAS Institute Inc. SAS user's guide: statistics. Version 5 ed. Cary, NC: SAS Institute Inc., 1985. 16. Fleiss JL. Statistical methods for rates and proportions. 2nd ed. New York: John Wiley & Sons, 1981; 217-9. 17. Snedecor GW, Cochran WG. Statistical Methods. 7th ed. Iowa: Iowa State University Press, 1980; 334:64. 18. Cox DR. Analysis of binary data. London: Methewen & ce., Ltd., 1970. 19. Woolcock AJ. Expression of results of airway hyperresponsiveness. In: Hargreave FE, Woolcock AJ, eds. Airway responsiveness: measurement and interpretation. Mississauga, ant: Astra, 1985;80-5. 20. Malo J, Pineau L, Cartier A, Martin RR. Reference values of the provocative concentrations of methacholine that cause 6010 and 20% changes in forced expiratory volume in one second in a normal population. Am Rev Respir Dis 1983; 128:8-11. 21. Weiss ST, Speizer FE. The epidemiology of asthma: risk factors and natural history. In: Weiss EB, Segal MS, Stein M, eds. Bronchial asthma. 2nd ed. Boston: Little Brown, 1985; 14-23. 22. Eggleston PA, Newill CA, Ansari AA, et af. Task-related variation in airborne concentrations of laboratory animal allergens: studies with Rat n I. J Allergy Clin Immunol 1989; 84:347-52. 23. O'Connor G, Sparrow D, Segal MR, WeissST. Smoking, atopy, and methacholine airway responsiveness among middle-aged and elderly men: the normative aging study. Am Rev Respir Dis 1989; 140:1520-6. 24. Burrows B, Lebowitz MD, Barbee RA. Respiratory disorders and allergy skin-test reactions. Ann Intern Med 1976; 84:134-9. 25. Corn M, Koegel A, Hall T, Scott A, Newill C, Evans R III. Characteristics of airborne particles associated with animal allergy in laboratory workers. Ann Occup Hyg 1988;32(Suppll:435-46). 26. Task force on Lung Dynamics. Deposition and retention models for internal dosimetry of the human respiratory tract. Health Physiol 1966; 12:173-85. 27. VenablesKM, TeeRD, Hawkins ER, et al. Laboratory animal allergy in a pharmaceutical company. Br J Ind Med 1988; 45:660-6. 28. Ziemann B, Corn M, Ansari A, Eggleston P. The effectiveness of the Duo-Flo BioClean unit for controlling airborne antigen levels. Am Ind Hyg Assoc J 1992; 53:138-45.
CAROL A. NEWILL, VALERIE L. PRENGER, JAMES E. FISH, RICHARD EVANS III, EARL L. DIAMOND, QINGYI WEI, and PEYTON A. EGGLESTON
A
Introduction
number of cross-sectional studies have examined the prevalence of airway hyperreactivity and the risk factors for this abnormality (1-9), but to date few have focused on the working age range 18to 55 yr (1,8,9). As part of a prospective study of the incidence of allergic asthma, we evaluated a large group of workers entering employment that involves exposure to laboratory animal allergens. This report presents cross-sectional data on potential risk factors for bronchial hyperreactivity among healthy young adults in this occupational setting. It specifically addresses the hypotheses that prior work experience and atopic status are risk factors for sensitization and disease. Methods Ascertainment of Subjects and Study Design Volunteers were research personnel (faculty, fellows, students, technicians) exposed to laboratory animals in their work in a medical research center. They were excluded if they had a history of symptomatic asthma with animal exposure, but they were not excluded if they had other allergic symptoms (e.g., rhinitis, conjunctivitis, rash). Symptomatic asthma was defined as the presence of at least three of the following symptoms: wheezing, breathlessness, chest tightness, or productive cough associated with workplace exposure. They were not excluded if they had these symptoms but could not relate them to the workplace. At enrollment in the study, volunteers underwent spirometry, methacholine challenge testing, allergen skin testing, and personal interviews. Potential study subjects were ascertained systematically through an extensive"Contact Network" made up of keypersons in each laboratory in which exposure to laboratory animals occurred, as well as the staff of the Occupational Health Office. Every 3 or 4 months, members of the Contact Network identified any persons newlyadded to the staff as well as any positions that were anticipated to be filled in the next year. In addition, current volunteers were asked to assist in the 1494
SUMMARY As a first step in a prospective stUdy of the Incidence of asthma to laboratory animals, a group of 364 adults 18 to 48 yr of age who were beginning employment with laboratory animals were evaluated In terms of their past history, health status, allergy, and airway responsiveness to methacholine. At entry to the stUdy, 269 had previous occupational contact with animals, 109 had chest symptoms In the previous year, 168 had a history of allergic symptoms to laboratory animals (any with asthmatic responses were systematically excluded), and 118had positive Immediate skin tests (29 had positive skin tests to laboratory animals). When defined as a PD,.FEV, of 80 breath units or less, 18.4% of these young adults had methacholine hyperresponslveness (HRA). Significant risk factors for HRA were found to be younger age, female sex, lower educational level, a history of allergic symptoms to laboratory animals, and a history of chest symptoms. Positive skin tests to laboratory animals were present in 8% of workers; this was not a significant risk factor for HRA although positive skin tests to pollen and household allergens were. PreviOUS work experience was a risk factor, especially among those with allergic symptoms, and a trend toward self-selection was suggested In that the rate of HRA was lowest In workers with more than 2 yr of experience or With AM REV RESPIR DIS 1992; 146:1494-1500 two or more previous jobs with laboratory animals.
ascertainment and recruitment of eligiblecolleagues. Potential subjects were recruited vigorously.
Pulmonary Function Testing Spirometry was performed according to ATS guidelines (10) using a rolling-seal spirometer (Model 822; Ohio Medical Products, Houston, TX). A technicallyacceptable spirogram met the following requirements: at least a 6-s duration, or 4 s if no change in the slope of the tracing; no cough in the first second; no cough affecting accurate measurements of the FVC; back-extrapolated volume less than 10070 of measured FVC. Measurements were corrected for BTPS. The best FEV, value of three satisfactory efforts was recorded and compared with predicted norms (11). Volunteers with FEV, 80070 or more of predicted proceeded to methacholine challenge testing. Methacholine challenges were performed according to a modification of the method of Chai and coworkers (12)and Fish and Kelly (13). Methacholine chloride (J. T. Baker Chemical Co., Phillipsburg, NJ) was prepared in 0.4% phenolated phosphate-buffered saline (PBS) (Hollister-Steir Laboratories, Spokane, WA) in concentrations of 1, 3, 10, and 25 mg/ml; for tests of subjects known to be highly reactive to methacholine, 0.25 and 0.5 mg/ml concentrations were prepared by onsite dilution. Aerosols were generated by a Model 646 nebulizer (DeVilbissCo., Somerset, PAl through a Rosenthal-French dosemetering device. Bronchodilators wereexclud-
ed for 24 h before the challenge. Volunteers inhaled five breaths of PBS, and FEV, was measured again. If this control value did not decrease by 10% or more, incremental concentrations of methacholine wereinhaled until FEV, decreased by 20% or more from control or until the 25-mg/ml solution was given. The dose causing a 20% fall in FEV, was interpolated from points on a log-linear dose-response plot and was designated the PD 2oFEV,_ This dose was expressed in breath units, where one breath unit (BU) is the equivalent of one inhalation of 1 mg/ml methacholine. (Received in original form June 26, 1991 and in revised form July 13, 1992) , From the Department of Immunology and Infectious Diseases and the Department of Epidemiology, The Johns Hopkins University School of Hygiene and Public Health, and the Department of Pediatrics, The Johns Hopkins UniversitySchool of Medicine,Baltimore, Maryland, the Department of Medicine, Jefferson Medical College, Philadelphia, Pennsylvania, and the Department of Pediatrics, Northwestern University School of Medicine, Chicago, Illinois. 2 Supported by Grant HL-30532 from the National Institutes of Health and by the Eudowood Fund of the Hospital for Consumptives of Maryland. 3 Correspondence and requests for reprints should be addressed to Peyton A. Eggleston, M.D., Department of Pediatrics, The Johns Hopkins Hospital, 600 North WolfeStreet, Baltimore,MD 21205.
1495
BRONCHIAL REACTIVITY IN LABORATORY ANIMAL WORKERS
Interview and Skin Jests Extensive, standardized, personal interviews, including questions regarding symptoms of allergy and asthma, wereadministered. Symptoms of asthma recorded were: intermittent episodes of wheezing, breathlessness (defined as episodes or attacks of difficulty in breathing, shortness of breath, or ability to take a deep breath), chest tightness (feeling of tightness or heaviness in the chest, possibly extending upward into the throat) and productive cough with sputum or phlegm (for at least 3 consecutive weeks). Immediate wheal and flare skin tests were performed by the prick-puncture technique of Santilli and coworkers (14). Materials included glycerinated extracts (1:20 wt:vol;Greer Laboratories, Lenoir, NC) of house dust, Alternaria, Aspergillus, short ragweed pollen, orchard grass pollen, and rat, mouse, guinea pig, and rabbit epithelium. Histamine phosphate 0.5 mg/ml was used as a positive control, and 500/0 glycerinated PBS (Hollister Steir) was used as a negative control. Tests applied in duplicate on the flexor surface of both forearms were read at 15 to 20 min. A positive test was defined as having at least one wheal ~ 4 mm in diameter, with the smaller wheal diameter ~ 2 mm. A valid skin test was defined as one in which the average wheal diameter of the two glycerine control tests was ~ 2 mm and the average wheal diameter of the positive controls was ~ 4 mm. All subjects denied receiving oral or nasal medications containing antihistamines within 48 h. Subjects Included in Analyses The target population was the estimated 1,200 people in the Johns Hopkins University who work with or use animals in their research or training, including students, faculty, research staff, and animal caretakers. The turnover rate among the staff is about 15% annually, 27% biennially, so that about 180 people begin working with animals at this institution each year. The study enrolled 504 subjects from this group. An additional 141 eligiblesubjects were contacted, but they refused to join the study, and 33 others refused to disclose sufficient information for assessment of eligibility. Of the 504 volunteers, 140 were excluded from the analysis because spirograms in their methacholine challenge tests on their initial visit were not sustained for a full 4 s and thus were not technically acceptable. These 140 differed from the remaining 364 only in having a larger proportion of women and a lower proportion with a history of allergic symptoms (see table 1). The 364 study subjects were 18 to 48 yr of age at the time of their initial test (median age, 26). Forty-six percent were women. Only 52 of 364 (14%) were current smokers at the time of their initial test, and 73% had never smoked. Most (316 of 364; 87070) were college graduates, and almost 50% (181 of 364)worked as research technicians. Although
TABLE 1 CHARACTERISTICS OF STUDY POPULATION WITH AND WITHOUT ACCEPTABLE METHACHOLINE CHALLENGE TESTS Acceptable Challenges (n 365)
=
Challenges not Acceptable(n 140)
=
(n)
(%)
(n)
(%)
P Value
119 245
32.7 67.3
46 94
32.9 67.1
0.972
166 198
45.6 54.4
80 60
57.1 42.9
0.020
52 45 267
14.3 12.4 73.3
22 15 103
15.7 10.7 73.6
48 163 153
13.2 44.8 42.0
28 50 62
20.0 35.7 44.3
0.024 0.194
181 183
49.7 52.3
58 82
41.4 58.6
0.095
279 55 30
76.6 15.2 8.2
109 21 10
77.9 15.0 7.1
0.888 0.801
95 159 110
26.0
43.7 30.3
39 59 42
27.9 42.1 30.0
168 196
46.2 53.8
41 99
29.3 70.7
0.001
109 255
29.9 70.1
52 88
37.1 62.9
0.121
Age, yr
18-23 24-48 Sex Female Male Smoking Current Past Never Educational level Below bachelors Bachelors Above bachelors Current job group Handler, tech Others Years in current job
2 Previous jobs with lab animals None
1 ;"2 History of allergy to lab animals t Yes No Chest symptoms; Yes No
ref
ref
ref 0.543
0.741 ref
ref
ref
ref 0.678
0.783 ref
ref
• Methacholine challenges were considered unacceptable when one or more spirograms were performed with an effort that was not sustainedfor 4 s or more. t Presence of allergicsymptoms (rhinitis, conjunctivitis, rashes) that could be relatedto exposureto a laboratoryanimal. :j: Historyof intermittentbreathlessness. Wheezing, chest tightness,or productivecough in the year prior to entry into the study.
most (269 of 364; 74%) had worked with animals in previous jobs, the majority (279 of 364) had worked in the present job for a year or less. Forty-six percent reported rhinitis, conjunctivitis, and/or skin rash on exposure to at least one species of laboratory animals; 109 (30%) had at least one chest symptom in the year prior to testing, but they could not relate these symptoms to animal exposure.
Analytic Methods Cross-sectional analysis of the frequency of airway hyperreactivity and its association with clinical, demographic, and occupational factors was performed using the SAS system (15) to perform chi-square tests, odds ratios and confidence intervals on odds ratios, and to calculate the probability that odds ratios differed from unity (16, 17). Results are presented in terms of both cross-sectional frequencies as well as the appropriate summary statistic, the odds ratio. Adjustment for age,
sex, and chest symptoms was carried out by logistic regression (18). Results
Frequency Distributions of Degree of Responsiveness As seen in figure 1, 67 volunteers (18.40/0) reacted to methacholine challenge with a PD2 0FEV 1 in the asthmatic range ~ 80 BU (19), and 18 (4.9%) were in the moderate to severe range (~ 20 BU). Risk Factors Associated with Hyperreactivity The proportion of subjects with HRA among those with and without risk factors at the time of enrollment in the study is shown in table 2. Being younger or female and having a lower educational level were significant risk factors for HRA. Tobacco smoking was not. Most subjects
1496
NEWILL, PRENGER, FISH, EVANS, DIAMOND, Wet, AND EGGLESTON
80 260
n=364
70 -"
60
i"
~
SO
u.
o rZ W
40 30
U
1 pack per day; these findings were similar among ex-smokers, of whom 64.4% reported ~ 1 pack per day and 6.6% > 1 pack per day. On-the-job experience with laboratory animals showed some trends with HRA. There was little difference in the frequency of HRA in workers employed as laboratory technicians or as animal handlers (29 of 181, 16%) when compared with faculty, students, postdoctorates, or administrators (38 of 183, 21%). However, the most experienced workers tended to have the lowest rates of HRA. For example, among the small number employed for more than 2 yr in their current job, only three of 30 (10%) had HRA compared with 17.6% of those in their first year and 27.3% ofthose in their second year of employment. The likelihood of having HRA was significantly greater among workers employed 1 to 2 yr relative to more experienced workers (odds ratio, 3.38; p = 0.036). A similar trend was seen among the 110 subjects who had held two or more previous jobs with laboratory animal exposure, of whom 15.4% had HRA compared with 23% of those with no previous job; how-
TABLE 2 RELATIONSHIP OF DEMOGRAPHIC AND OCCUPATIONAL CHARACTERISTICS AND ALLERGY HISTORY TO AIRWAY HYPERREACTIVITY (HRA) HRA Positive' Risk Factor at Entry
Odds Ratio
95% CI
P Value
26.9 14.2
2.21
1.40-3.47
0.002
42 25
25.3 12.6
2.34
1.48-3.71
0.001
48 163 153
12 34 21
25.0 20.9 13.7
2.10 1.66
1.07-4.10 1.04-2.83
0.035 0.049
52 45 267
12 5 50
23.8 11.1 18.7
1.30 0.54
0.71-2.37 0.24-1.23
0.235 0.110
181 183
29 38
16.0 20.8
0.90
0.68-5.39
0.351
279 55 30
49 15 3
17.6 27.3 10.0
1.92 3.38
0.68-5.39 1.10-10.30
0.150 0.036
95 159 110
22 28 17
23.2 17.6 15.4
1.65 1.17
0.91-2.97 0.67-2.03
0.082 0.321
168 196
38 29
22.6 14.8
1.68
1.07-2.64
0.028
Number
(n)
(%)
364
67
18.4
119 245
32 35
166 198
Total group Age group, yr
18-23 24-48 Sex Female Male Education level Below bachelors Bachelors Above bachelors Smoking Current Past Never Current job group Handler, tech Others Years in current job
.. 1 > 1 to 2 >2 Previous jobs with lab animals None
1 ;;.2 History of allergy to lab animals t Yes No
ref
ref
ref
ref
ref
ref
ref
ref
• Defined as PD"FEV, .. 80 breath units.
t Defined as rhinitis, conjunctivitis, and/or rash with exposure to any animal(s) in the workplace.
ever, this comparison did not reach statistical significance (odds ratio, 1.65; p = 0.082). That these trends toward the lowest cross-sectional frequency of HRA were found among the workers with the most previous laboratory animal job experience suggests that those with HRA had left the work force in greater numbers before entering this study. A positive history of allergy to animal(s) in the workplace (defined as complaints of rhinitis, conjunctivitis, and/or rash) was associated with HRA, as 23% of 168 subjects with symptoms had HRA compared with 15% of 196 denying such symptoms (p = 0.028). The relationship between experience in the workplace and HRA was seen most strongly among the 168 subjects with a history of allergic symptoms to laboratory animals, as shown in table 3. For example, among the 32 subjects who had held no previous jobs working with laboratory animals (i.e., were in their first such job), 38% had HRA compared with 14% of those 65 who had held two or more jobs (odds ratio, 3.73; p = 0.009). The association between workplace experience and HRA was much weaker among the 196 subjects who denied a history of allergy to laboratory animals. As shown in table 3, the corresponding odds ratio was only 0.87 (p = 0.70). A similar trend was seen when the frequency of HRA was related to workers' length of experience in their current job. These trends suggest that workers with a history of allergic symptoms and HRA, i.e., those most likelyto havechest symptoms, were less apt to continue working with animals or to take another job with animal exposure. As seen in table 4, the presence of a positive skin test was associated with more frequent HRA. Of 355 volunteers who had valid skin tests to inhalant allergens, 118 had a positive response to any allergen. Only 29 (8%) had positive skin tests to any of four common laboratory animal allergens, even though nearly half of the workers reported allergic symptoms associated with laboratory animal exposure. Seventy-sevenvolunteers (22%) had positive skin tests to household allergens, including 31 with positive reactions to cat and/or dog allergens. A positive skin test to cat or dog allergen was associated with a positive skin test to laboratory animal allergens (rat, rabbit, mouse, and/or guinea pig); of the 31 subjects who reacted to cat and/or dog allergens, eight (36%) also reacted to laboratory animal allergens,
BRONCHIAL REACTIVITY IN LABORATORY ANIMAL WORKERS
1497
TABLE 3
reporting any two or more symptoms (odds ratio, 4.63; p < 0.0001). Among the demographic characteristics of the participants, the two most strongly associated with HRA (younger age and female) could in turn influence other variables such as smoking, time on the job, education, and job title (i.e., younger subjects and women tended to have attained less education) and their relationship to HRA. Therefore, logistic regression analyses were carried to adjust for the effect of each of these two variables. The relationships between the other risk factors and HRA after adjustment for age and sexseparatelyare shown in table 6. For instance, the association with educational background, whereby in workers with less education there was a greater number with HRA, disappeared when adjusted for age or sex.The association between positive skin tests to pollen allergens and HRA was strengthened somewhat when adjusted for sex (odds ratio 2.64; p = 0.0008); this related to a much higher frequency of positive skin tests among men (520/0 versus 28%). The relationship between HRA and several risk factors, notably, history of allergy to laboratory animals, the presence of two or more chest symptoms, and skin test sensitivity to pollens or to laboratoryanimals, wasnot altered by adjustment for age or sex. Also shown in table 6 are the results of reanalyzing the risk factors with adj ustment for the presence of chest symptoms. This was done both because the presence of chest symptoms was such a strong risk factor for HRA and because the presence of chest symptoms might influence work behavior or the relationship of allergy and HRA. This adjustment diminished the association between time in the current job and HRA, i.e., the odds ratio for 1 to 2 yr previous experience compared with more than 2 yr decreased from 3.38 to 3.06 and was no longer significant. When adjusted for chest symptoms, the effect of allergy to laboratory animals, either as indicated by history or by skin test sensitivity to animal allergens, was diminished as well.
INTERRELATIONSHIP OF PAST HISTORY OF ALLERGIC SYMPTOMS ASSOCIATED WITH LABORATORY ANIMALS TO LABORATORY ANIMAL EXPOSURE HISTORY AND TO AIRWAY HYPERREACTIVITY (HRA) HRA Positive'
(Ok)
Odds Ratio
95% CI
p Value
25 12 1
21 38 7
3.65 8.40
0.56-160 0.98-384
0.172 0.027
12 17 65 9 No history of allergy to laboratory animals, n = 196
38 24 14
3.73 1.96
1.21-11.7 0.75-5.42
0.009 0.100
0.24-11.3 0.10-13.2
0.602 0.702
0.28-2.81 0.22-2.07
0.702 0.861
Number
(n)
Positive history of allergy to laboratory animals, n Years in current job
2 Previous jobs with lab animals None
32 71
1 ;'2
ref
ref
Years in current job
2
158 23 15
24 3 2
15 13 13
1.16 0.98
63 88 45
10 11 8
16 13 18
0.87 0.66
Previous jobs with lab animals None
1 ;'2
ref
ref
, Defined as PD"FEV, " 80 breath units. Defined as rhinitis, conjunctivitis, and/or rash with exposure to any animal(s) in the workplace.
t
compared with only 21 of 324 (6%) who did not react to cat or dog allergen (chi square, 14.1; p = 0.0001). Although skin test reactivity to pollens and laboratory animals appeared to be related to each other (odds ratio, 7.17; p < 0.0001), cross tabulation of the two categories of allergens in table 4 showed that only pollen skin test reactivity, and not laboratory animal allergen reactivity, was associated with HRA cross-sectionally.
Not surprisingly, in the subjects who in their initial interview reported having two or more chest symptoms to any trigger during the year before enrollment in the study there was a significantly greater number with HRA than in those subjects who denied such symptoms (see table 5). Breathlessness was the single symptom most strongly associated (odds ratio, 4.12; p < 0.0001), but HRA was detected in almost half (20 of 45) of those
TABLE 4 RELATIONSHIP OF SKIN TESTING RESULTS TO HRA HRA Positive' Number Valid skin test t Laboratory animals:!: Positive Negative Pollans§ Positive Nagative Perennial household allergensll Positive' Negative Skin test to animals and/or pollen allergens + animall + pollen + animal/- pollen - animal! + pollen - animal/- pollen
Odds Ratio
95% CI
p Value
31.0 17.2
2.17
0.82-5.29
0.061
31 34
27.7 14.0
2.35
1.30-4.22
0.002
77 278
29 36
37.7 13.0
4.06
23 6 89 237
7 2 24 32
30.4 33.3 27.0 13.5
2.80 3.20 2.37
(n)
(Ok)
355
65
18.3
29 326
9 56
112 243
raf
ret 2.17~7.52
< 0.0001
0.90-7.87 0.28-23.3 1.23-4.47
0.039 0.199 0.004
raf
Discussion
ref
• Defined as PD"FEV, " 80 breath units.
t Mean glycerine wheal" 2 mm, mean histamine wheal .. 4 mm.
*Rat, rabbit, mouse, and/or guinea pig.
§ Grass and/or ragweed. II Dust, Alternaria, cat, and/or dog. , Larger wheal .. 4 mm in diameter, smaller wheal" 2 mm In diameter. or, if only one arm tested, than" 4 mm.
This report shows that the frequency of HRA, as defined by methacholine PD zoFEVl ~ 80 BU, was 18.4% in this group of young adult laboratory workers. This figure is similar to prevalence rates in other series of adults and children, which have ranged from 17.9% (3) to 28% (2). The frequency seen with any
1498
NEWILL, PRENGER, FISH, EVANS, DIAMOND, WEI, AND EGGLESTON
TABLE 5 RELATIONSHIP OF CHEST SYMPTOMS IN THE LAST YEAR TO HRA HRA'
Breathlessness Yes No Wheezing Yes No Chest tightness Yes No Productive cough Yes No Any of four symptoms Yes No Two or more symptoms Yes No
Number
(n)
(%)
Odds Ratio
95% Cl
P Value
45 319
19 48
42.2 15.1
4.12
2.36-7.22
< 0.0001
52 312
16 51
30.8 16.4
2.35
1.35-4.10
0.006
47 317
16 51
34.0 16.1
2.69
1.40-4.74
0.002
28 336
8 59
28.6 16.1
1.88
0.91-3.89
0.077
109 255
29 38
26.6 14.9
2.07
1.31-3.28
0.005
45 319
20 47
44.4 14.7
4.63
2.65-8.09
< 0.0001
ref
ref
ref
ref
ref
ref
, Defined as PD"FEV, .. 80 breath units.
test for airway reactivity obviously depends on the criteria for a positive response (19). Our definition is based on the work of others, which has shown that greater than 95% of current asthmatics (9) and only 3010 of a population selected to exclude asthmatics (20) will have an abnormal response. Our population was similar to others, and it was unselected except that recruitment was based on anticipated exposure to laboratory animals and that workers with a history of asthma on exposure to laboratory animals wereexcluded. The latter requirement was required by the overall design to study prospectively the development of clinically significant asthma reaction to animals in the workplace over a period of time. The association of HRA with younger age and with the female sex in this
TABLE 6 ADJUSTED RISK FACTORS FOR HRA HRA Positive' Risk Factor at Entry Total group Age group, yr
18-23 24-48 Sex Female Male Education level Below bachelors Bachelors Above bachelors Smoking Current Past Never Current job group Handler, tech Others Years in current job
1 to 2 >2 Previous jobs with lab animals None
1 ;'2 History of allergy to laboratory animals Yes No Two or more chest symptoms in past year Yes No Positive skin tests to pollen allergensII Yes No Positive skin tests to animal allergens Yes No
Sex-adjusted
Age-adjusted
Number
(n)
(%)
364
67
18.0
119 245
32 35
26.9 14.2
166 198
42 25
25.3 12.6
2.29
48 163 153
12 34 21
25.0 20.9 13.7
1.23
52 45 267
12 5 50
23.8 11.1 18.7
1.49 0.67
181 183
29 38
16.0 20.8
0.63
279 55 30
49 15 3
17.6 27.3 10.0
1.55 2.82
95 159 110
22 28 17
23.2 17.6 15.4
1.26 0.96
168 196
38 29
22.6 14.8
1.58
45 319
20 47
44.4 14.7
4.52
112 243
31 34
27.7 14.0
2.32
29 326
9 56
31.0 17.2
2.42
Odds Ratiot
p Value
Odds Ratio
p Value
Odds Ratio*
p Value
2.15
0.003
2.14
0.008
2.24
0.002
*
0.004
ref
ref
0.30
ref §
1.77 1.33
0.08 0.19
0.14 0.21
ref
0.051
ref
§
1.06 0.55
ref
ref
1.29
0.58
0.24
0.03
1.71 3.23
0.19 0.04
0.26 0.45
1.81 1.25
0.05 0.06
0.05
1.68
0.03
< 0.0001
4.43
1.77 3.06
0.35 0.10
1.56 1.17
0.23 0.65
1.48
0.16
ref
ref
ref
0.09
ref
ref
ref
0.62
0.88 0.22
ref
ref
ref
0.20 0.009
ref
ref
0.24 0.07
1.76 1.67 ref
ref
< 0.0001
ref
ref
0.003
2.64
0.0008
0.053
2.42 ref
2.30
0.005
ref
ref
ref
, Defined as PD"FEV, .. 80 breath units. Odds ratios were adjusted on age groups 18 to 23 yr (n = 119)and 24 to 48 yr (n = 245). Presence of two or more chest symptoms in past year (wheezing, breathlessness, chest tightness, productive cough). § Cell size did not allow valid calculation of odds ratio. II Positiveskin test = larger wheal", 4 mm in diameter, smallerwheat", 2 mm in diameter, or, if only one arm tested, then", 4 mm.
t
ref
ref
ref
Symptom-adjusted
0.054
1.94 ref
0.20
BRONCHIAL REACTIVITY IN LABORATORY ANIMAL WORKERS
study was unexpected and cannot be explained easily. Age-dependent variations among adults have been addressed in only a few other studies; older age has been associated with greater degree of reactivity to methacholine among men, most of whom had occupational exposure to air contaminants associated with increased risk of asthma (8), whereas in a series of asymptomatic, nonsmoking men and women, no difference was seen with age (20). However, separate reports of HRA in adults and in children would suggest that the prevalence is higher among children and young adults (4,5). In our data, the age difference was related in part to job experience, as older workers tended to have been employed in their current job longer and to have had more previous jobs with laboratory animal exposure. Probably because of the healthy worker effect, these workers tended to have been self-selected for lack of airway hyperreactivity or its associated symptoms. Given the higher prevalence of symptomatic asthma in men (21), it was surprising to find a higher frequency of HRA among women in our study. Two other studies have addressed sex as a risk factor for HRA (5, 7) and found no difference; however, Malo and colleagues (20) did find a small but significantly higher rate among women in a series of asymptomatic, nonsmoking normal volunteers. We evaluated several possible explanations for the association. For instance in our series, it is possible that women and subjects with less education may have been more likely to have jobs that would expose them to higher concentrations of animal allergens (22), or they may have had less mobility in their jobs. Indeed, when educational level was examined as a risk factor with adjustment for sex, the association with HRA was diluted, indicating an interaction between sex and educational level and risk of HRA. This suggests that the sex difference in HRA may have an environmental basis. Two risk factors that we found associated with HRA were those identified in previous population studies, i.e., positive allergy skin tests (23) and a history of chest symptoms (2). A history of asthma symptoms in the year prior to enrollment in the study was found to be associated with more than a 4-fold increased risk of HRA. However, the personal interview reporting of asthma symptoms was not highly predictive of HRA, as only 44OJo of those with ahistory of two or more recent symptoms had
demonstrable HRA. On the other hand, only 15% of 319 subjects without such a history had HRA. Both of these figures are consistent with the findings of others. For instance, Asher and colleagues (4), using the same definition of HRA, found that 43% of children with current symptoms consistent with asthma had HRA compared with 11 % of those without symptoms. Dales and colleagues (6), using a modified American Thoracic Society questionnaire, found that a history of ever wheezing was associated with HRA, with a specificity of 87% in an occupational sample in which 21% had airway reactivity. Burney and Chinn (2), using the International Union Against Tuberculosis questionnaire, found that a history of wheezing in the previous year was associated with HRA, with a specificity of 72% in a sample enriched for history of wheezing; this corresponded to a frequency of HRA of 55% in subjects answering "yes" and 7% in those answering "no." Without a gold standard, it is difficult to determine which of the two instruments, the questionnaire or the bronchoprovocation, is more useful for categorizing our participants as asthmatic, but our data clearly support the conclusions of other investigators (2, 7) that airway reactivity bears only a loose relationship to asthmatic symptoms in a population. Skin test reactivity to pollen and common household allergens was associated with HRA. This is consistent with the observations of Burrows and colleagues (24) and O'Connor and coworkers (23) that positive skin tests are associated with an increased frequency of asthmatic respiratory symptoms (24) and of HRA (23). Indeed, the statistically significant odds ratio of 2.35 between pollen skin test reactivity and HRA seen in our study was remarkably similar to the odds ratios of 3.0 and 3.3 observed by Peat and colleagues (3) in two Australian towns. In contrast, evidence of IgE reactivity to laboratory animal allergens in skin tests was not significantly associated with increased risk of HRA. The differences between plant pollen and animal dander allergen include the biologic and physical characteristics of the particles that bear the allergenic constituents. Our published data (25) show that a large proportion of particles bearing rat allergen have aerodynamic equivalent diameters ~ 1.3 11m, a size that allows penetration of the peripheral airways and air spaces. Although comparable data on aerodynamic characteristics of pollen particles are not available, the reported characteristics of
1499
pollen grains suggest that their distribution in lung may differ (26). The possibility that there are as yet unidentified differences in host immunologic reactivity to plant versus animal allergens also merits study. However, a more likely explanation is that the pattern of exposure to pollens and to laboratory animals differs in that pollen exposure is seasonal and lifelong, whereas laboratory animal exposure may be continuous on a day-to-day basis, but it does not occur for as many years. In this study, only 30 of 364 had been employed in their current job for more than 2 yr at the time of enrollment, and only 110 of 364 had held two or more prior jobs that entailed exposure to laboratory animals. Thus, our subjects, in addition to limiting their exposure to a few hours a day, had generally been exposed to animal allergens for less than 2 yr, so that the relationship to animal allergens was just emerging. This explanation is supported by our finding that the prevalence of HRA in these workers (18.9%) was similar to that in other populations (2, 3). The trend seen between workers with more than 2 yr of job experience and declining risk of HRA suggests a selfselection bias, sometimes called the healthy worker effect. Workers developing HRA in the workplace may incur symptomatic reactions to animals, causing them to move to other jobs with less or no exposure to animals. This would result in a lower frequency of HRA among those who have been on the job longest or who have held the greatest number of jobs in this workplace. Our data suggest that such an effect may have occurred, and this is consistent with the work of Venables and colleagues (27) with regard to atopic status in a crosssectional study of laboratory animal workers in England. The possibility of a self-selection bias in our cross-sectional analysis supports the hypothesis that chronic occupational exposure to laboratory animal allergens may lead to generalized airway reactivity to nonspecific stimuli such as methacholine, and that such hyperactivity may precede the development of clinically diagnosed asthma to the original, precipitating allergen(s). Prospective analyses of the risk of developing clinically significant asthma among laboratory-animal-exposed workers with and without HRA will help to elucidate these relationships. These data have implications for the management oflaboratory animal aller-
1500
NEWILL, PRENGER, FISH, EVANS, DIAMOND, WEI, AND EGGLESTON
gy and asthma in the workplace. First, they suggest that at any point in time, many laboratory animal workers have airway symptoms, positive allergy skin tests, and methacholine sensitivity; the prevalence of these manifestations is similar to that in the general population. Thus, preemployment screening procedures are likelyto be neither efficient nor effective in selecting a work force with lower risk for laboratory animal asthma. On the other hand, experienced workers without disease do appear to be a more distinct group. After only 1 to 2 yr of job exposure, it would appear that some of the symptomatic workers have removed themselves from the workplace. This trend probably cannot be changed and appears to produce a work force that is less likely to become symptomatic on the job. If it is not possible to screen effectively for high risk workers, the most obvious and logical step in prevention is to limit exposure to the allergen. In addition to maintaining good ventilation in laboratories and vivaria, it is important to use appropriate allergen control devices during high risk activities such as surgery and cage cleaning (22, 28) and to insist on the more general use of protective clothing and masks. Acknowledgment The writers would like to thank Alice Rodman for her contributions to the data collection and management and Barbara Wheeler for her help in preparing the manuscript.
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Immunol 1980; 65:406-14. 15. SAS Institute Inc. SAS user's guide: statistics. Version 5 ed. Cary, NC: SAS Institute Inc., 1985. 16. Fleiss JL. Statistical methods for rates and proportions. 2nd ed. New York: John Wiley & Sons, 1981; 217-9. 17. Snedecor GW, Cochran WG. Statistical Methods. 7th ed. Iowa: Iowa State University Press, 1980; 334:64. 18. Cox DR. Analysis of binary data. London: Methewen & ce., Ltd., 1970. 19. Woolcock AJ. Expression of results of airway hyperresponsiveness. In: Hargreave FE, Woolcock AJ, eds. Airway responsiveness: measurement and interpretation. Mississauga, ant: Astra, 1985;80-5. 20. Malo J, Pineau L, Cartier A, Martin RR. Reference values of the provocative concentrations of methacholine that cause 6010 and 20% changes in forced expiratory volume in one second in a normal population. Am Rev Respir Dis 1983; 128:8-11. 21. Weiss ST, Speizer FE. The epidemiology of asthma: risk factors and natural history. In: Weiss EB, Segal MS, Stein M, eds. Bronchial asthma. 2nd ed. Boston: Little Brown, 1985; 14-23. 22. Eggleston PA, Newill CA, Ansari AA, et af. Task-related variation in airborne concentrations of laboratory animal allergens: studies with Rat n I. J Allergy Clin Immunol 1989; 84:347-52. 23. O'Connor G, Sparrow D, Segal MR, WeissST. Smoking, atopy, and methacholine airway responsiveness among middle-aged and elderly men: the normative aging study. Am Rev Respir Dis 1989; 140:1520-6. 24. Burrows B, Lebowitz MD, Barbee RA. Respiratory disorders and allergy skin-test reactions. Ann Intern Med 1976; 84:134-9. 25. Corn M, Koegel A, Hall T, Scott A, Newill C, Evans R III. Characteristics of airborne particles associated with animal allergy in laboratory workers. Ann Occup Hyg 1988;32(Suppll:435-46). 26. Task force on Lung Dynamics. Deposition and retention models for internal dosimetry of the human respiratory tract. Health Physiol 1966; 12:173-85. 27. VenablesKM, TeeRD, Hawkins ER, et al. Laboratory animal allergy in a pharmaceutical company. Br J Ind Med 1988; 45:660-6. 28. Ziemann B, Corn M, Ansari A, Eggleston P. The effectiveness of the Duo-Flo BioClean unit for controlling airborne antigen levels. Am Ind Hyg Assoc J 1992; 53:138-45.
