17, 102- 115 (1978)
Heat Wave Mortality MICHAEL Institute
of Environmental 550 First
Medicine. New York University Medical Avenue, New York, New York 10016
Received August 12, 1977 Patterns of mortality in 11 air-conditioned and 9 un-air-conditioned nursing homes in New York City have been investigated to determine the impacts of heat waves on nursing home occupants and the efftcacy of air conditioning in reducing these impacts. During each of four heat waves in 1972 and 1973, the number of deaths in un-ah-conditioned nursing homes was significantly greater than the number of deaths expected on the basis of mortality during cooler control periods. In contrast, deaths in air-conditioned nursing homes were not sign&antly different from expected. The age- and sex-adjusted ratio of relative death rates was 2.29 (95% confidence interval = 1.75-2.98). Approximately 94 excess deaths occurred in the un-airconditioned nursing homes. On the basis of this research, it is recommended that nursing homes and other institutions for the elderly located in climates like that of New York City be required to provide air conditioning.
INTRODUCTION Heat waves, periods of abnormally high atmospheric temperature, are frequently associated with dramatic short-term increases in mortality rates. The increase in mortality in a large urban area during a heat wave can be quite severe: Schuman (1972) estimated that 1181 excess deaths occurred during a 16day heat wave in New York City in 1%6. Ellis et al. (1975) reported similar effects during two less severe heat waves in 1972 and 1973. The means by which to control heat wave mortality, it would seem, exist in air conditioning. However, inasmuch as the association between heat waves and mortality has remained essentially constant over the last 20 years despite the proliferation of air conditioning (Marmor, 1975), current evidence fails to support an important protective effect of this technology for the population as a whole. The continued presence of excess mortality during heat waves in the 1970s may be due in part to a lack of air conditioning in situations where it could be most effective, as in institutions for the sick and elderly. Since there has been no research on the effects of air conditioning on mortality in such institutions, the present study compares mortality among occupants of au--conditioned and un-airconditioned nursing homes in Ney York City. The purposes of the study are: (1) to determine if excess mortality during heat waves is less in air-conditioned nursing homes than in un-air-conditioned nursing homes, and (2) if so, to estimate how many deaths in un-air-conditioned nursing homes could have been postponed if air conditioning had been in operation. A secondary purpose is to develop a methodology which might permit investigation of the effects of environmental stresses other than heat, such as air pollution, on nursing home occupants. 1 Present address: Department of Preventive Medicine, New York State College of Veterinary Medicine, Cornell University, P.O. Box 786, Ithaca, N.Y. 14850. 102 OOl3-9351/78/0171-0102$02.00/O Copyright @ 1978 by AcademrL Press, Inc. All rights of reproduction in any form reserved.
METHODS AND MATERIALS The method of excess mortality (Schuman, 1972) was used to compare the effects of heat waves on mortality in air-conditioned and un-air-conditioned nursing homes. This method contrasts the number of deaths, ni, which occur in an area during a period of interest lasting dl days, with the number of deaths, n,, which occur in the same area during a control period lasting d, days. It is assumed that the size, age distribution, and other relevant characteristics of the populations at risk are approximately equal during the two periods. The relative death ‘rate, R, during the period of interest compared with during the control period is estimated by R = (ni/dJ / (nJd,). The excess deaths, E, during the period of interest is estimated E = ni - (nJdJ
(1) by (2)
In short, the method of excess mortality uses a population as its own control. Applying the method to nursing homes thus assumes that certain characteristics of the populations at risk in the nursing homes remain reasonably constant between heat waves and control periods. These factors include occupancy, average state of health of residents, and daily rate of transfer of dying residents from the nursing homes to other health care institutions. The assumption of constancy in these factors is reasonable when the heat wave and control periods are close in time and relatively short in duration. Definition of Heat Waves and Control Periods The National Climatic Center provided temperatures measured at the Central Park Observatory in Manhattan between May 1 and September 30, 1972 and between May 1 and September 30, 1973. Ellis et al. (1975) had previously identified two heat waves in these periods. In the present study heat waves were defined to be periods during which the maximum daily temperature on each of 4 or more consecutive days exceeded 88°F (31.1”(Z). Since peaks in daily mortality during heat waves generally lag the corresponding peaks in maximum temperature by 1 day, an additional day after the periods of high temperature was also included in each heat wave (Kutschenreuter, 1960). Two control periods, one for 1972 and one for 1973, were defined to include all days, D, between May 1 and September 30, for which 1. Tmax (0) s 85°F (29.4”(Z), 2. Tmax (D - 1) 4 85°F (29.4”C), 3. T,,, (D-2 through D-7) G 88°F (31.1”C), where T,,, (0) is the maximum temperature on Day D. The purpose of these criteria was to eliminate from the control periods both immediate and delayed effects of heat on mortality. Mortality Data The New York City Department of Health provided computer-coded death certificate data for all persons who died in New York City in the years 1972 and
1973. For each death, the coded information included institution of death, cause of death (National Center for Health Statistics, 1967), age, sex, and race of the decedent. For a nursing home to be included in the study, three criteria had to be met. First, 15 or more deaths had to have occurred in the nursing home in each of the periods May 1 through September 30, 1972, and May 1 through September 30, 1973. A minimum of 15 deaths was chosen for convenience, yielding a manageable number of nursing homes yet a sufficient number of deaths for analysis. Second, the nursing home had to be either totally air conditioned or totally un-airconditioned in the summers of 1972 and 1973. Air-conditioning status was determined by telephone interview with the administrator of the nursing home, the medical director, or, in one instance, the chief engineer. Air-conditioning information was verified whenever possible through interviews with inspection officials of the New York State Department of Health. However, New York State first assumed responsibility for New York City nursing homes in 1973 and data from this source for 1972 and 1973 were either unavailable or uncertain for several of the nursing homes. The third criterion for admission of a nursing home to the study was that the nursing home could not be a facility devoted solely to the care of patients with a particular disease. Such nursing homes were excluded because their occupants might have higher or lower susceptibility to heat than that of a heterogeneous nursing home population. After choosing the study nursing homes according to the above criteria, they were compared with one another by examining each nursing home’s cause, age, sex, and race distributions of deaths. Average death rates per thousand bed-days were also compared, these rates being computed from the total number of deaths occurring in each nursing home over the entire study period, May 1 through September 30, of 1972 and 1973, and the number of beds in each nursing home as obtained from published sources (Health and Hospitals Planning Council of Southern New York, Inc., undated-a, -b; National Center for Health Statistics, 1975). Relative death rates (R) were calculated for each nursing home for each heat wave according to Eq. (1). Deaths from all nursing homes were then pooled into two groups, those occurring in air-conditioned nursing homes and those occurring in un-air-conditioned nursing homes. In this part of the analysis, “risk ratios” were investigated in addition to R values. The risk ratio, RR, was defined as the R in the un-air-conditioned group of nursing homes divided by the R in the airconditioned group of nursing homes, or [(Ni/DJl(NJoJ] / [(ni/dJl(nJd,)], where capital letters denote data for un-air-conditioned nursing homes and lower case letters denote data for air-conditioned nursing homes. Since the heat wave and control periods were of the same duration in all nursing homes (Q = di; D, = d,) this expression simplifies to RR = (Nilni) I (NC/n,).
The risk ratio is thus identical to the relative odds of a fourfold table with elements Ni, nip N,, and n, (i.e., a table of deaths in un-air-conditioned and airconditioned nursing homes by heat wave or control period). Adjusted risk ratios
and confidence intervals were calculated according to the standard methods for fourfold tables (Mantel and Haenszel, 1959; Miettinen, 1976). Unlike the relative death rate, the risk ratio provides a measure of airconditioning effectiveness which is adjusted for concurrent forces affecting mortality rates in both groups of nursing homes irrespective of the presence or absence of air conditioning. Examples of such forces are environmental stresses other than heat, such as influenza epidemics, air pollution episodes, or heat exposures experienced by occupants of both air-conditioned and un-air-conditioned nursing homes, as for instance might occur during walks outside the nursing homes. The risk ratio will retain a degree of adjustment for such factors even if the populations at risk are only roughly comparable. RESULTS
Choice and Comparability of Study Nursing Homes Twenty-eight nursing homes met the criteria of having 15 or more deaths during the period May I through September 30, 1972, and 15 or more deaths during the same period in 1973. Twenty-one of these were either totally air-conditioned or totally un-air-conditoned during the study period, according to interviews with nursing home officials. New York State inspection officials were able to verify this information for 13 of the 21 nursing homes. One of the twenty-one nursing homes was devoted entirely to terminal cancer care and thus was excluded from the study. Of the remaining 20 nursing homes, 11 were air-conditioned during the periods of interest and 9 were un-air-conditioned. Table 1 compares the air-conditioned nursing homes to the un-air-conditioned nursing homes in terms of average size, type of care offered, mortality rates, and mean ages at death. The average size of the air-conditioned homes, 313 beds, was less than the average of 387 beds in the un-air-conditioned homes. Column 2 shows the number of beds in each nursing home which were healthrelated facility (HRF) beds. The remainder in each nursing home were skilled nursing facility (SNF) beds. HRF beds are intended for residents who do not require full-time nursing attention and can thus be assumed to be less ill than the SNF patients who are provided with such care (Health and Hospitals Planning Council of Southern New York, Inc., undated-a). Nineteen percent of the beds in the un-air-conditioned nursing homes were HRF beds, while 6% of the beds in the air-conditioned homes were HRF beds. The average death rates in each of the individual nursing homes and in the two groups of nursing homes (air-conditioned and un-air-conditioned), shown in column 3, were roughly comparable, indicating similar populations. Nursing home NO. 7, however, did have a substantially higher death rate than the others. The mean ages at death in the study nursing homes, shown in column 5, were all between 80 and 85 years except for home No. 6 which had a mean age at death of 75.2 years. The mean ages at death of the two groups of homes were significantly different (P < O.OOl), the air-conditioned homes having a younger age at death than the un-air-conditioned nursing homes. Age-adjusted comparisons (Mantel and Haenszel, 1959) were therefore made in the analysis. An additional comparison of the homes is given in Table 2, where the proportion of mortality due to each of three major causes of death is shown for
TABLE NUMBER IN STUDY
Nursing home no. (1) A. Air-conditioned
1 2 3 4 5 6 I 8 9 10 11
Total B. Un-air-conditioned
12 13 14 15 16 17 18 19 20
AT DEATH AND
Death rate (deaths/ 1008 bed-days) (4)
Mean age at death (years) (5)
0.59 0.72 0.51 0.41 0.61 0.89 1.63 0.72 0.51 0.53 0.95
81.1 79.7 81.1 84.4 80.0 75.2 79.9 80.8 81.9 85.0 80.7
260 520 246 295 509 517 364 482 280
120 210 268 80
0.73 0.53 0.64 0.70 0.58 0.64 0.55 0.94 0.46
80.2 80.6 85.6 80.3 85.1 84.5 82.4 85.3 80.8
Number of bedsa Total
(2) 499 407 205 522 320 504 1% 173 200 240 179
a Sources: Health and Hospitals Planning Council of Southern New York, Inc. (undated-a, -b); National Center for Health Statistics (1975). b Health-related facility beds.
each home and for each group of homes. The air-conditioned homes had a higher proportion of deaths from cancer than the un-air-conditioned homes, while the unair-conditioned homes had higher proportions of deaths due to cardiovascular diseases and pneumonia and influenza. The mean ages at death for each of the three causes were less in the air-conditioned nursing homes than in the un-airconditioned nursing homes. Cancer deaths in the air-conditioned nursing homes had the youngest mean age at 75.5 years. The sex distribution of deaths in the study institutions revealed that females predominated in the individual nursing homes and in both groups of nursing homes. Females accounted for 71.9% of all deaths in the group of air-conditioned nursing homes and 64.0% in the un-air-conditioned group. The nursing home deaths were also predominantly white-%% in the air-conditioned nursing homes and 94% in the un-air-conditioned nursing homes. Un-air-conditioned nursing home Nos. 12 and 13 had 79 and 76% white deaths, respectively, and were the only nursing homes in the study reporting less than 85% white deaths.
OF DEATHS DUE TO CANCER (ICD 140-209), 390-448), AND PNEUMONIA AND INFLUENZA
479-474, 480-486) IN STUDY NURSING MAY 1 - SEFTEMBER 30, 1972 AND
1973” Deaths (%)
Nursing home no. 1 2 3 4 5 6 7 8 9
Total or average ,Mean age at death (years) B . Un-air-conditioned
12 13 14 15 16 17 18 19 20
Total or average Mean age at death (years) a ICD, International
Number of deaths
90 90 32 66 60 138 98 38 31 39 52 734 80.1 58 84 48 63 90 102 61 138 39
17 20 13
Pneumonia and influenza 6 8 3 3 2 32 5 13 3 3
73 58 72 77 78 34 73 58 71 87 75 65 81.8 78 76 83 71 63 75 57 60 92
25 9 13 16 8 12 16 75.5 7 5 6 5 2 7 10
9 80.2 9 15 8 5 31 6 10
Classification of Diseases.
While the two groups of nursing homes were not strictly comparable to each other, the comparison of heat wave effects between them still provides a degree of control for coincident events as explained earlier. Stratification of the analysis was used to control for the differences in age and sex between the two groups of homes. In addition, heat wave effects were examined within each set of nursing homes without reference to the other set via the R values. Heat Waves and Control Periods
One period in 1972 and three periods in 1973 met the criteria for heat waves. The dates and maximum daily temperatures of the heat waves are shown in Table 3. Although there were electric power failures in portions of New York City during the 1972 heat wave and during the first and third heat waves in 1973 (New York Times), only nursing home Nos. 8 and 18 during the 1972 heat wave were near any of the “blackout” areas. Records of the local power company indicate,
TABLE DATES AND MAXIMU
Heat wave no.
OF STUDY HEAT WAVES”
Maximum daily temperatures (“W
Average maximum temperature (“F)
July 14-26, 1972
89,93,90,92,89, 94,88,92,92,94, 91,91,80
June 9- 13, 1973
July 7-11, 1973
August 288September 1973
n Temperatures were measured at the Central Park Observatory.
however, that these two nursing homes were not affected by the power outage (D. Mormile, Consolidated Edison Co., personal communication, January 30, 1978). Eighty days in the period May 1 through September 30, 1972, met the criteria for control days, while 73 days in the period May 1 through September 30, 1973, met these same criteria. The average maximum temperature during the 1972 control period was 72.6”F (22.6”C); during the 1973 control period the average maximum temperature was 74.9”F (23.8”C). The control periods included days before and after each of the heat waves studied. Analysis of Individual Nursing Homes
Table 4 shows the relative death rate (Z?) calculated according to Eq. (1) for each nursing home during each of the four study heat waves. Two out of the 44 R values in the air-conditioned nursing homes were significantly greater than 1 (Z’ < 0.05), while 12 out of the 36 R values in the un-air-conditioned nursing homes were significantly greater than 1. Analysis of Grouped Data
The mortality data were next analyzed by grouping the deaths into those which occurred in air-conditioned nursing homes and those which occurred in un-airconditioned nursing homes. Table 5 shows that all four heat waves were associated with R values significantly greater than 1 in the un-air-conditioned nursing homes, while none of the R values in the air-conditioned nursing homes were significantly greater than 1. For the four heat waves combined, the R values were 2.73 in the un-air-conditioned nursing homes and 1.18 in the air-conditioned nursing homes. The risk ratios (RR), which were adjusted for age and sex, varied from 2.0 to 3.0, depending roughly on the average maximum temperature of the heat wave. A summary RR of 2.29 was calculated for the four heat waves combined. Analysis of the sex distribution of heat wave mortality (Table 6) indicated that death rates increased more among male residents of un-air-conditioned nursing homes than among female residents. However, male deaths also increased more than female deaths in the air-conditioned nursing homes. As a result, the age-
TABLE RELATIVE EACH
Relative death rate (ZZ) Nursing home no. A. Air-conditioned 1 2 3 4 5 6 7 8 9 10 11 B. Un-air-conditioned 12 13 14 15 16 17 18 19 20
72-1” nursing homes: 1.68 1.61 1.03 1.54 1.37 1.oo 0.80 0.95 0.56 4.40* 1.37 nursing homes: 14.77** 4.10** 1.23 3.59* 1.85 3.26* 1.54 1.05 2.46
1.62 2.74 6.26* 1.33 3.65 2.43 -
-b 1.83 1.62 1.04 0.66 3.65 2.09
1.35 1.01 1.16 1.01 1.80 0.39 1.11 2.03 6.08 1.74
1.04 3.65* 5.21* 4.44** 4.87
2.43 2.09 2.43 2.09 4.56* 2.09 1.12 1.27 2.43
4.06* 0.58 0.68 8.11** 2.53 5.21** 1.87 5.64** 2.70
a Heat wave No. b A - means that no deaths occurred during the heat wave period, so the relative risk is undetined. * P < 0.05, two-tailed test. ** P < 0.01, two-tailed test.
adjusted RR values for males and females were remarkably similar, at 2.2 and 2.4, respectively. In this and in subsequent tables, the four heat waves were combined and compared with the combined control periods. Analysis of the ages at death (Table 7) indicated that the R values in the un-airconditioned nursing homes and the RR values were greatest in the youngest age group (~69 years) and decreased with increasing age. The R values in the airconditioned nursing homes seemed to follow an opposite pattern, being lowest in the youngest age group and increasing somewhat with increasing age. Separate analyses by four major categories of cause of death are shown in Table 8. The largest R in the un-air-conditioned nursing homes and the largest RR were for “other” causes of death. The 25 “other” deaths which occurred in the un-airconditioned nursing homes during the four heat waves included three deaths due to excess heat [International Classification of Diseases (ICD), 9901 and two deaths due to diabetes (ICD 250). There were no deaths due to these two causes in the air-conditioned nursing homes during the heat waves, or in either set of nursing homes during the control periods. The “other” category also included four deaths due to falls in the un-air-conditioned nursing homes during the heat waves.
Relative death rate (R)” Heat wave no.
Air-conditioned nursing homes
72- 1 73-l 73-2 73-3
1.33 1.05 0.96 1.17
All heat waves
Un-air-conditioned nursing homes
(39)C (12) (II) (24)
2.65** 2.37** 2.25** 3.47**
(62)’ (19) (18) (50)
Risk ratio (RR)b 2.01 2.22 2.00 3.05
(1.25-3.24)d (0.95-5.22) (0.80-5.01) (1.75-5.32)
a Calculated according to Eq. (1). There were 80 and 73 days during the 1972 and 1973 control periods, respectively. The numbers of days in heat waves 72-1, 73-1, 73-2, and 73-3 were 13, 5, 5, and 9, respectively. b Calculated according to Eq. (2), adjusted for age at death (