757

STATE-OF-THE-ART CLINICAL ARTICLE

Infections Caused by Chlamydia pneumoniae Strain TWAR J. Thomas Grayston

From the Department of Epidemiology. University of Washington. Seattle. Washington

Chlamydia psittaci because it clearly was not Chlamydia trachomatis and did have a few characteristics similar to those of C. psittaci. Subsequent studies have resulted in its classification as a new species, Chlamydia pneumoniae. Two findings are the most important in distinguishing TWAR as a species. First, there is < I0% DNA homology between TW AR and strains of the other two species, whereas all isolates of C. pneumoniae have >90% homology. Second, the morphology of the TW AR elementary body on electron micrography shows a pear shape with a periplasmic space, while both other species have round elementary bodies with little or no periplasmic space. Table I presents some characteristics and properties of the three chlamydial species. While the clinical illnesses caused by C. pneumoniae and C. trachomatis do not overlap (with C. trachomatis pneumonia occurring only in infants), both C. pneumoniae and C. psittaci cause pneumonia. Both of these species may elicit complement-fixing (CF) antibody with chlamydial antigen, but pneumonia due to TW AR is much more common. C. pneumoniae is more homogeneous than the other two species. All isolates tested are immunologically similar; representative strains from different countries have been examined by molecular fingerprinting and found to be identical; and major outer-membrane proteins of strains from the United States, Japan, and Finland have been sequenced and found to be identical. Only one strain or serovar of C. pneumoniae has been identified. Therefore, at this time, the name of the strain, TWAR, is synonymous with the designation C.

Why Is TWAR Considered a New Species?

Respiratory illnesses. The name Chlamydia pneumoniae was chosen for the new species because pneumonia was the clinical syndrome most frequently associated with TWAR infection. Pneumonia and bronchitis remain the most frequent of the recognized illnesses associated with TWAR, although asymptomatic infection or unrecognized, mildly symptomatic illnesses are the most common result ofTWAR infection. The patient's age at the time of infection influences the clinical syndrome. Pneumonia due to TW AR is more common among the elderly and less common among persons 19

No. of acute rises"

No. of person-years

0 14 15 2 6

27 lSI 242 91 394

NOTE. Table is adapted from [2]. '" Fourfoldrise in antibody titer. t Rate per 100 person-years at risk.

Incidence'

9.2 6.2 2.2 1.5

6

... (0

*

5

f.

... G)

c.

0 0

S ...

TWAR+

M.Pneumoniae *

4 3

G)

c. 2

G)

(0

IX

0 0

10

20

30 40 50 Age in years

60

70

>

Figure 3. Incidence of pneumonia, by age, for two etiologic agents (M. pneumoniae and C. pneumoniae). The population studied was the Group Health Cooperative of Puget Sound; the period covered was 1963-1975.

References I. GraystonJT, Kuo C-C,WangS-P. et al. A new Chlamydia psittaci strain

TWAR, isolated in acute respiratory tract infections. N Engl J Med 1986;315:161-8. 2. Aldous MB, Grayston JT. Wang S-P. Fay HM. Seroepidemiology of Chlamydia pneumoniae in Seattle families. 1966-1979. J Infect Dis 1992;166:646-9.

SuggestedReadings AugenbraunMH, Roblin PM,Mandel U. Hammerschlag MR, SchachterJ. Chlamydia pneumoniae pneumonia with pleural effusion: diagnosis by culture. Am J Med 1991;91:437-8. Campbell LA, Melgosa MP, Hamilton DJ, Kuo C-C, Grayston JT. Detection of Chlamydia pneumoniae by polymerase chain reaction. J Clin MicrobioI1992;30:434-9. Grayston JT. Kuo C-C, Campbell LA, Wang S-P. Chlamydia pneumoniae sp. nov. for Chlamydia sp. strain TWAR. Int J Syst Bacteriol 1989;39:88-90. GraystonJT. Campbell LA, Kuo C-C, et al. A new respiratory tract pathogen: Chlamydia pneumoniae. strain TWAR. J Infect Dis 1990;161 :61825. Hammerschlag MR. Chirgwin K. Roblin PM.et al. Persistent infectionwith Chlamydia pneumoniae following acute respiratory illness. Clin InfectDis 1992;14:178-82. Saikku P, Leinonen M. Tenkanen L, et al. Chronic Chlamydia pneumoniae infectionas a risk factor for coronaryheart disease in the Helsinki Heart Study. Ann Intern Med 1992;116:273-8. Shor A, Kuo C-c' Patton DL. Detectionof Chlamydia pneumoniae ui coronary arterial fatty streaks and atheromatous plaques. S Afr Med J 1992;82:158-61. ThornDH,GraystonJT, Siscovick DS.WangS-P. Weiss NS, DalingJR.Association of prior infection with Chlamydia pneumoniae and angiographically demonstrated coronary arterydisease. JAMA 1992;268:68-72.

Downloaded from http://cid.oxfordjournals.org/ at Yale University on July 15, 2015

of reinfection. Five persons had more than one episode of TWAR infection, and the majority of adults with new infections (10 of 16) had had serum antibody detected earlier [2]. TWAR pneumonia incidence. We studied the incidence of TWAR pneumonia and M. pneumoniae pneumonia in 1963-1975 in a defined population in Seattle (the Group Health Cooperative of Puget Sound). In those studies we found an average annual incidence of pneumonia of 1.2/ 100, with isolation of M. pneumoniae or serological evidence of M. pneumoniae infection in 17% of cases. When nearly 2,000 paired serum specimens from the study were tested, 10% showed evidence ofTWAR infection. The age curve of incidence for both etiologicagents (figure 3) showedthat the incidence of M. pneumoniae pneumonia was highest among older children, while that ofTWAR pneumonia was highest among the elderly. This age-related difference was reflected in the higher rate of TWAR infection (11.4%) than of M. pneumoniae infection (4.5%) among the patients with pneumonia (16% of the total) who were hospitalized. Periodicity. TWAR infectionsare both endemic and epidemic. It appears that TWAR periodicity consists of intervals of increased incidence (epidemics) superimposed on a basic endemicity. We have seen periods of increased incidence of 2-3 years' duration as well as shorter outbreaks of several months. Periodsoflow incidence have usually lasted for 3-4 years. Transmission. C. pneumoniae is believed to be transmitted from human to human by respiratorytract secretions, but direct evidence is lacking. Spread of the infection is slow. The case-to-case interval has averaged 30 days. Epidemics in closed populations have lasted for 6 months. It appears that many infected persons are ineffective transmitters of the organism and that some persons with asymptomatic infections playa role in spread of the disease.

Age (y)

761

C. pneumoniae Strain TWAR

CID 1992;15 (November)

762

This test affords you the opportunity to assess your knowledge and understanding of the material presented in the preceding clinical article "Infections Caused by Chlamydia pneumoniae Strain TWAR," authored by J. Thomas Grayston, and to earn continuing medical education (CME) credit. As an organization accredited by ACCME to provide continuing medical education, the Department of Continuing Education in Health Sciences, UCLA Extension, certifies that this CME activity meets the criteria for 1 hour in Category I ofthe Physician's Recognition Award ofthe American Medical Association and the California Medical Association Certificate in Continuing Medical Education. To earn credit, read the State-of-the-Art Clinical Article carefully and answer the following questions. Mark your answer by circling the correct responses on the answer card (usually found toward the front of the issue) and mail after affixing first class postage. To earn credit, a minimum score of 80% must be obtained. Certificates of CME credit will be awarded on a per volume (biannual) basis. Each answer card must be submitted within 3 months of the date of issue. This program is made possible by an educational grant from Roche Laboratories. 1. Which is the most frequent clinical response to TW AR infection? A. Pneumonia B. Bronchitis C. Fever of undetermined origin D. Pharyngitis with laryngitis E. Asymptomatic infection or unrecognized, mildly symptomatic illness

SION 2. Which of the following is least frequently found at presentation with TW AR disease? A. Fever B. Cough C. Hoarseness D. Rhonchi or rales E. Elevated erythrocyte sedimentation rate 3. The incidence of TW AR infection has been increasing worldwide since the organism was first isolated in 1965. True = A; False = B. 4. Which of the following is/are true? A. The onset of TW AR pneumonia may be biphasic, with pharyngitis followed in days or weeks by pneumonia or bronchitis. B. Pleuritis and pleuritic fluid may accompany more severe TW AR pneumonia. C. Onset of asthma may follow TWAR infection. D. TW AR infection may be no more apt to be followed by asthma than are some other respiratory infections. E. The elderly have a higher prevalence ofTWAR antibody than do 5- to 14-year-olds. 5. Which of the following is/are true of antibiotic treatment of TW AR infection? A. A high dosage (2 g/d) and a prolonged course (1014 d) are required. B. Tetracycline may be used. C. Macrolides may be used. D. A second course may be required. E. A sulfa drug should not be used. 6. The common laboratory test for antibody to C. psittaci differentiates psittacosis from TW AR infection. True = A; False = B.

Downloaded from http://cid.oxfordjournals.org/ at Yale University on July 15, 2015

uc~

C1D \992; \5 (November)

CME Test

7. C. pneumoniae and C. trachoma tis differ from each other in which one or more of the following characteristics? A. Sexual transmission B. Cause of pneumonia in adults C. Humans as only host D. Number of serovars 8. Which of the following is/are often found with TWAR pneumonia? A. Outpatient treatment B. Accompanying symptoms of pharyngitis C. Accompanying symptoms of sinusitis D. Single subsegmental pneumonitis on chest radiograph E. Increased incidence in the elderly

763

9. Data suggest that, on average, about I in 14 children 5-14 years of age is infected with TW AR each year. True = A; False = B. 10. Which of the following statements is/are true? A. TW AR infections are both epidemic and endemic. B. TWAR infections are periodic, usually with several years of low incidence. C. Persons with symptomatic or asymptomatic TWAR infections efficiently transmit the organism to others. D. TW AR is spread from human to human without an intermediate bird or animal host. E. On the basis of case-to-case intervals, the incubation period for TW AR appears to be long. Downloaded from http://cid.oxfordjournals.org/ at Yale University on July 15, 2015

Infections caused by Chlamydia pneumoniae strain TWAR.

757 STATE-OF-THE-ART CLINICAL ARTICLE Infections Caused by Chlamydia pneumoniae Strain TWAR J. Thomas Grayston From the Department of Epidemiology...
604KB Sizes 0 Downloads 0 Views