ASSOCIATIONS OF CORONARY AND STROKE MORTALITY WITH TEMPERATURE AND SNOWFALL IN SELECTED AREAS OF THE UNITED STATES,

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1 AMERICAN JOURNAL OF EPIDEMIOLOGY Copyright 6 by The Johns Hopkins University School of Hygiene and Public Health Vol 03, No 6 Printed in U.SA. ASSOCIATIONS OF CORONARY AND STROKE MORTALITY WITH TEMPERATURE AND SNOWFALL IN SELECTED AREAS OF THE UNITED STATES, -6 EUGENE ROGOT AND STEPHEN J. PADGETT Rogot. E.. and S. J. Padgett (NHLI. NIH. Bethesda. MD 00). Associations of coronary and stroke mortality with temperature and snowfall in selected areas of the United States. -6. Am J Epidemiol 03: Daily temperatures and snowfall were related to coronary and stroke deaths in selected standard metropolitan statistical areas for the -year period -6. Typically an inverse approximately linear pattern of coronary heart disease (CHD) and of stroke mortality with temperature was seen over the greater part of the temperature range, with mortality reaching a low for days with average Fahrenheit temperatures in the 60's and 70's ( C). and then rising sharply at higher temperatures. Snowfall was found to be associated with higher CHD and stroke mortality for a - or 6-day period. Temperatures and days prior to death were also found to be associated with deaths from CHD and stroke. Very hot days appeared to exert a cumulative effect upon mortality in many of the areas. coronary heart disease; mortality; stroke; weather Speculation on the effects of climate upon health goes back at least to Hippocrates and his "Air, Waters and Places" (). Only in recent years, with the careful and complete recording of vital and medical events and the weather, has it been possible to relate on a daily basis such figures as deaths from disease to average temperature for a city. Some of the earliest studies in the United States in which daily mortality and weather data were used appear to have been those of Justin () and of Huntington (3), who both covered mortality and weather in New York City for the years -. More recently, studies in Received for publication August,, and in final form October 9,. Abbreviations: CHD, coronary heart disease; SMSA, standard metropolitan statistical area. Epidemiology Branch, Division of Heart & Vascular Diseases, National Heart & Lung Institute, NIH, Landow Building, Room C-, Bethesda, MD 00. The authors thank Robert W. Buechley and John B. Van Bruggen for providing the basic tapes, and Charles E. Sydenstricker for invaluable programming help in the early stages of this study. 6 temperate climates here and abroad (-) have shown the characteristic pattern for total mortality and for cardiovascular mortality to be one with high mortality in the winter and low mortality in the summer. Exceptions to the usual pattern are the studies by Heyer et al. (), reporting increased frequency of acute myocardial infarctions in the summer in Dallas, Texas; DePasquale and Burch (3) reporting similarly for New Orleans, Louisiana; and Avierinos () with similar findings for Cairo and all of Egypt. The present study is a sequel to studies of cardiovascular mortality as related to weather in Memphis for 9- () and in Chicago for 7 (6, 7). In both studies the weather variable most strongly associated with coronary heart disease (CHD) mortality was the daily average temperature. In Chicago, an inverse linear relationship was observed between temperature and CHD deaths. Snowfall also appeared to be an important factor. With temperature

2 66 ROGOT AND PADGETT controlled, positive associations were noted for CHD deaths and snowfall. The patterns observed for temperature and snowfall held mainly for men. For stroke deaths, no clear-cut relationship to the daily temperature emerged in Chicago, although in Memphis an inverse relationship had been reported. A number of questions raised in the above studies suggested a study of more areas for longer periods of time. The major goals of the present study] are to investigate the association of CHD deaths, and of stroke deaths, with daily temperature and snowfall in selected standard metropolitan statistical areas over a five year period, and to explore associations by sex, age and area. MATERIALS AND METHODS Mortality data for the United States for the five years, -6, were made available to us by the National Center for Health Statistics (NCHS). This is the most recent period in which day of death was coded by the NCHS. The causes studied in this paper are CHD (ICD #0, 7th Revision) and stroke (ICD #330-33, 7th Revision). A total of 3 standard metropolitan statistical areas (SMSA's) were initially chosen for study. Resident deaths in these areas with underlying cause of death given as either CHD or stroke were selected. The choice of an SMS A rather than a city as the basic unit of study seemed appropriate since these mortality data were available and temperature and snowfall data as reported by the Weather Bureau for the central city in the SMSA could be used to cover the entire SMSA. The areas chosen for study are given in table, along with the total number of CHD and stroke deaths in the five year period, the average daily temperature and numbers of snowfall days. The 3 areas were chosen from the 0 SMSA's designated in the 0 census as follows: First, the largest areas, those with more than million population, were chosen. Next, high snowfall areas with moderately large populations were chosen. Here it seemed appropriate to include SMSA's fairly close to one another. Next, areas with hot climates and of moderately large size were chosen. Here again, several areas fairly close to one another were included. A number of areas were then chosen in an attempt to improve the geographic representation of the United States. Finally, certain areas were chosen because of their unique climates. In all, the 3 SMSA's included about 0 per cent of the US population. RESULTS Figure shows average numbers of CHD deaths per day for each area according to " 3 00 B i 0 0 U SO 0 UD F -o -7 ii n a c AVBWH laobutube ON OAT Of DEATH EO BD -S -U X FIGURE. Average daily deaths from CHD by average temperature on day of death for 3 selected SMSA's: US, -6.

3 WEATHER AND CORONARY AND STROKE MORTALITY 67 the average (mid-range) temperature in 0-degree units Fahrenheit (equivalent to.6-degree units centigrade) on the day of death. The 7 areas on the left side of figure are considered our "snow areas," with snowfall days ranging from 6 in Washington, D.C. to 3 in Buffalo (table ). By contrast the areas on the right side experienced few if any snow days over the five-year period. The vertical scale in figure is logarithmic to allow for direct comparisons between areas of relative changes and to present a more compact set of graphs. The numbers of days by temperature ranges for each area are given in table. TABLE Overall, these graphs are remarkably consistent by area. An inverse approximately linear (or log-linear) pattern of CHD mortality with temperature is seen over the greater part of the temperature range with mortality reaching a low for days with average Fahrenheit temperatures in the sixties and seventies ( C), and then rising sharply. This pattern holds for of the 7 snow areas (Denver and Salt Lake City are the exceptions). Excepting Honolulu and possibly Memphis the warmer areas show the same basic pattern. However, for the warmer areas, the low mortality point occurs at 0-9 F Deaths from CHD and stroke, average daily temperature and number of snowfall days for 3 selected SMSA's' US, -6 SMSA Atlanta Boston-Lowell-Lawrence Buffalo Chicago Cleveland Dallas Denver Detroit Honolulu Houston Los Angeles-Long Beach Memphis Miami Milwaukee Minneapolis-St. Paul New Orleans New York Omaha Philadelphia Phoenix Pittsburgh Portland, Oreg-Wash Rochester St. Louis Salt Lake City San Antonio San Diego San Francisco-Oakland Seattle Syracuse Tampa-St. Petersburg Washington, D.C.-Md.-Va. CHD 0,7 7,7,,00 9,006,,,6,9 3,,73 6,6,67 7, 0,76 3,66,606 7,06 6,6,3,,66,3 3, 3,0 6,76,6, 6, 0,3 6,7,66 Deaths from Stroke,9 6,6 6,7,63,6,30 3, 6,37,06,37 36,0,0,66 6,0,37,3,06,3 0,006,7 3,7 6,077 3,3,37,,769, 3,03 6,3, 7,66 7,00 Average daily F(C) temperature 60(.6) (0.6) 7 (.3) (0.6) 9 (9.) 66( 9) 0(0.0) 0 (0.0) 77 (.0) 70 (.) 6(6.7) 6 (6.7) 76 (3 9) 6 (7.) (6 7) 6 (0.0) (.) (.) 3(.7) 70(.) 0(0 0) 3(.7) (.9) (.) (0.6) 69 (0.6) 63(7.) 6(3.3) (.) 7 (.3) 7 (.) 7 (3.9) Days under 0 F {A A C*\ with \t i \jf witn snowfall

4 6 ROGOT AND PADGETT TABLE Frequency distribution of days by daily average temperature 3 selected SMSA's, US, -6 DayB by daily average temperature SMSA,^ Below (F) _ 9-9 to - Oto 9 0 to 9 0 to 9 30 to 39 0 to 9 0 to to to 79 0 to 9 90+,«> Below (C) - - to - -7 to - - to -7-6 to - Oto 3 to 9 0 to 6 to 0 to 6 7 to 3 on. SZ + Atlanta Boston Buffalo Chicago Cleveland Dallas Denver Detroit Honolulu Houston Los Angeles Memphis Miami Milwaukee Minn-St.Paul New Orleans New York Omaha Philadelphia Phoenn Pittsburgh Portland Rochester St. Louis Salt Lake San Antonio San Diego San Francisco Seattle Syracuse Tampa Washington ( C) for Miami, Tampa, Houston and Phoenix. Also, there was no upturn in mortality at the hot temperatures for Miami and Tampa. Figure presents stroke deaths versus temperature for the 3 areas, as in figure. We note first that the numbers of stroke deaths in each area are much smaller than the numbers of CHD deaths, and for this reason alone, underlying patterns for stroke would be more affected by random fluctuation than those for CHD. In general, the patterns seen for stroke are quite similar to those described for CHD. The main differences are for mortality at the coldest temperatures. Considering just that portion of each curve for days with average temperature under 0 F (under. C), six of the 7 snow areas showed peak mortality at their lowest temperature points and six showed peak mortality at their second lowest points. The corresponding numbers for CHD were and, respectively. For the warm areas, this distinction between stroke and CHD is not as evident. At higher temperatures, comparing fig-

5 WEATHER AND CORONARY AND STROKE MORTALITY JO IS 7 3 -«-7 II 7 I C AVBWE TWBUTURE ON MY Of DEATH FIGURE. Average daily deaths from stroke by average temperature on day of death for 3 selected SMSA's: US, -6 ure with figure, there is a tendency for areas to experience even sharper rises in mortality for stroke than for CHD. This tendency appears to be especially pronounced for the larger SMSA's. It may also be seen in figures and that warmer areas tend to show greater mortality excesses on cold days than do colder areas. Similarly, colder areas tend to exhibit greater mortality excesses on hot days than do warmer areas. It should be noted that the rightmost and leftmost points of figures and in many areas may be based on small numbers of deaths and days. Of the 3 SMSA's, 7 were studied for possible effects of snowfall upon mortality. These are the areas on the left side of figures and. Preliminary analyses indicated positive associations between snowfall and mortality for the day of the snowfall and for several days afterward. As a result we calculated mortality averages on days under 0 F (under. C) for the following non-overlapping categories of days: day* with snowfall; days,, 3,, and 6 following the most recent snowfall; and 7 or more days following the most recent snowfall. The average daily mortality (for each area) for the group 7 or more days'from any snowfall was used as "control," i.e., the average for days under 0 F unaffected by snowfall. The number of areas (out of 7) for which the mortality averages in the first 7 categories were in excess of the control average were as follows: CHD Stroke Snowfall day 7 Days after most recent snowfall Note that each entry here is an independent statistic, and under the null hypothesis that snow and mortality are not associated, each statistic has an expected value of.. Using the control averages, we calculated expected numbers of deaths in each of the other categories by multiplying the number of days in a given category by the control average. These expected numbers can be compared to the observed numbers of deaths to measure the effect of the snowfall. These results are summarized in figure 3. Since days of and following snowfall tend to be somewhat colder than the other days under 0 F, the data were also adjusted for temperature. (The method of adjustment is described in the footnotes to table 3.) In the case of stroke, no noticeable change was observed. In the case of CHD, values for the excesses were in almost every instance smaller by amounts from.0 to.0. Both figure 3 and the text table above show that snowfall is related to mortality on the day of the snowfall and for several days after. For stroke there is a substantial

6 70 ROGOT AND PADGETT SI UK days under 0 F which follow most recent snowfall by six or more days. Ratios of O to E are given in table 3. For both diseases, almost all SMSA's show mortality excesses during the snow periods CHD in Denver was the only exception. Out of 7 cities, 0 show statistically significant excesses for CHD and MY ABB) MOST RHHfT SNOWFAU For Oqn Wift Amp Tmpnlini Unda 0 F (. a ie 0 JE FIGURE 3. Mortality excesses for CHD and stroke in 7 SMSA's on days of and after snowfall by amount of snowfall: US, -6. O O, light snow (< inch; <. cm); A A, medium snow, (-.9 inches;. cm-.7 cm); A, heavy snow (+ inches; >.7 cm). O = total observed deaths over 7 SMSA's; E = total expected deaths over 7 SMSA's based on averages for days under 0 F which follow snowfall by at least 7 days. Points are not shown for "heavy snow, days 3,, and 6 since not all 7 areas had days in these categories. and uniform mortality excess lasting from the day of the snowfall until five days after. However, mortality appears to be related only weakly to amount of snowfall. For CHD, there is a substantial mortality excess on the day of the snowfall and on the first day after. For two through four days after snowfall, CHD shows weak but statistically significant association. CHD mortality is strongly related to amount of snowfall. To summarize the association of snow with CHD and stroke, we tabulated observed (O) deaths and calculated expected (E) numbers of deaths on days under 0 F during a six-day snow period includes snowfall day and days,, 3,, after most recent snowfall. A five-day snow period would have been sufficient for CHD, but six was used in order to make direct comparison with stroke. Expected numbers were based on mortality averages of TABLE 3 Ratios of observed (O) to expected (E)* numbers of CHD and stroke deaths for days under 0 F (. C) during the 6-day snow period, 7 SMSA's. US, -6 SMSA Boston Buffalo Chicago Cleveland Denver Detroit Milwaukee Minn-StPaul New York Omaha Philadelphia Pittsburgh Rochester St Louis Salt Lake Syracuse Washington Total Total (temperature adjusted) CHD O/E O/E.09*.* *.07*.0* *..9*.03.0* 06* ].7* *.0*.0* ].0*.* *.06* L.0 L.0 ] 3*. L.ll.07* ] L.36* L.07* L.0 L.09 penodf * E based on daily mortality averages of days under 0 F which follow the most recent snowfall by 6 or more days t Snowfall period includes snowfall days and days,, 3,, after most recent snowfall. * Statistically significant at.0 level. Total ratio is found after O and E were accumulated over all areas. No statistical tests of significance were done on totals. I Each area was adjusted separately by an indirect method using for standard "rates" the average daily deaths for days following the most recent snowfall by 6 or more days. Temperature categories used were: less than 0 F, 0-9 F and F (less than -6.7 C, -6.7 through -. C and -. through.3 C). The adjusted values of E were accumulated over all areas in order to find the adjusted total O/E.

7 WEATHER AND CORONARY AND STROKE MORTAUTY 7 for stroke. The totals indicate that overall, stroke mortality is affected relatively more than CHD. Temperature adjustment results in a reduction in the overall excess for CHD but not for stroke. Thus some of the mortality excess for CHD during the snow period may be due to colder temperatures. Since snowfall was associated with higher CHD and stroke mortality for a - or 6-day period, we decided to study the possible prolonged effects of cold or hot days upon mortality as well. For this purpose each day was first classified into one of five broad categories: A - Average temperature <0F with snowfall B - Average temperature <0F with no snowfall C - Average temperature 0-9 F ( - C) D - Average temperature F ( C) E - Average temperature 0 F + (6.7 C+) Next, each day was classified according to its temperature-snowfall and the temperature-snowfall of the day before. This gives, theoretically, possible kinds of days AA, AB, AC,..., DE, EE, with the first letter indicating the weather of the previous day and the second the weather of the current day. Similarly, we may consider one day's weather as made up of the temperature-snowfall of that day and the two previous days. Each day can then be represented by a three-letter group such as AAA, AAB, etc., with the initial letter denoting the weather two days ago, the second letter indicating yesterday's weather and the third letter indicating today's weather. Table presents summary data for the simplest case (A, B, C, D, E days); table shows data for selected pairs and table 6 for selected three-letter groups. The areas were divided as shown in tables and on the basis of similarity of temperature ranges (see table ). The figures shown are averages of index numbers which were prepared initially for each area. The index numbers for a given area were calculated by dividing the average deaths per day for each weather category by the average deaths per day over the five-year period for that area, and multiplying the result by TABLE Average index numbers for CHD and stroke deaths by weather on day of death for selected groups of SMSA's- US, -6 Average atureand snowfall on day ofdeath* A B C D E A B C D E 7 snow areas} Average index numberet for Portland, Los 9 warm San Angeles, areas} Francisco. San Seattle Diego CHD Stroke Honolulu A - Average temperature <0 F (<. C) with snowfall. B «. Average temperature <0F with no snowfall. C - Average temperature 0-9 F (.-. C). D - Average temperature F ( C). E - Average temperature 0 F+ (6.7 C+). f Index numbers were first calculated for each area by dividing the average daily CHD (and stroke) deaths in given weather categories by the average daily CHD (and stroke) deaths in the -year period and multiplying by. Averages were then obtained by summing the appropriate index numbers and dividing by the number of areas in the group. Includes Boston, Buffalo, Chicago, Cleveland, Denver, Detroit, Milwaukee, Minneapolis, New York, Omaha, Philadelphia, Pittsburgh, Rochester, St. Louis, Salt Lake, Syracuse and Washington, D.C. } Includes Atlanta, Dallas, Houston, Memphis, Miami, New Orleans, Phoenix, San Antonio and Tampa. I Based on areas.. Index numbers based on less than 0 deaths were not included in calculating averages. The averages obtained give equal weight to each area. The data in table recapitulate much of the previous material. For the 7 snow areas, for CHD and for stroke, we have A>B>C>D and D<E. For the nine warm areas we have B>C>D>E for CHD; for stroke, B>C>D butd <E. Port-

8 7 ROGOT AND PADGETT TABLE Average index numbers for CHD and stroke deaths by type of weather on day of death in terms of yesterday's and today's average temperature and snowfall, for selected groups of SMSA's US, -6 Average temperature and snowfall on day of death* AA BA CA AB BB CB AC BC CC DC CD DD ED DE EE AA BA CA AB BB CB AC BC CC DC CD DD ED DE EE 7 enow areas 0 0t 0 09* 0 0 ** 9 t 9 warm areas 3} CHD Stroke Portland, San Francisco, Seattle ft 0 Los Angeles, San Diego ** ** ** Honolulu * See table for list of areas, description of weather categories A, B, C, D, E and average index numbers Each pair of letters is taken as a single day with a weather component from yesterday (the first letter) and a weather component from today (the second letter) and is related to deaths today. t Based on areas * Based on areas Based on 6 areas. H Based on 7 areas I Based on 6 areas. * Based on areas ft Based on areas. ** Based on Los Angeles only. TABLE 6 Average index numbers for CHD and stroke deaths by type of weather on day of death in terms of average temperature and snowfall days ago, yesterday and today: 7 SMSA's, US, -6 Average temperature and snowfall on day ofdeath* AAA BAA ABA BBA CBA CCA AAB BAB ABB BBB CBB BCB CCB BBC CBC BCC CCC DCC CDC DDC CCD DCD CDD DDD EDD DED EED DDE DEE EEE CHD 6 f * 03* f 0 0f } Stroke * 06 HO* * * 03 0 * 09 * * 0* " } 3** * See table for list of areas, description of weather categories A, B, C, D, E and average index numbers. Each 3-letter group is taken as a single day with a weather component from days ago (the first letter), a weather component from yesterday (the second letter) and a weather component from today (the third letter) and is related to deaths today t Based on areas. * Based on 6 areas. } Based on areas. Based on 0 areas. I Based on 3 areas * Based on areas. land, San Francisco and Seattle show B>C>D for both CHD and stroke. Los Angeles and San Diego resemble the snow areas in that OD but D<E.

9 WEATHER AND CORONARY AND STROKE MORTALITY 73 CHD and stroke show similar overall patterns but differ in that highest mortality usually occurs for CHD on the coldest days while for stroke highest mortality may occur on the hottest days. For the 7 areas, average index numbers range from for D days to for A days for CHD and from on D days to 6 on E days for stroke. Table shows that yesterday's weather is associated with deaths today from CHD and stroke. Thus, for the 7 snow areas, controlling on today's weather, we have AA>BA>CA, AB>BB>CB, AC>BOCC >DC, CD>DD but ED>DD and EE>DE. Average index numbers range from on DD days to on AA days for CHD and from 9 on DD days to on EE days for stroke. Controlling on yesterday's as well as today's weather, table 6 indicates that the weather two days ago is also associated with today's mortality but the associations are not as consistent as before. Thus, for the 7 snow areas (for CHD and for stroke), ABB > BBB > CBB and BCC > CCC > DCC but CBA>BBA. For these areas, the average index numbers range from 9 on DDD days to 6 on AAA days for CHD and from 9 on DDD days to 3 on EEE days for stroke. Studying longer weather strings involving the previous three, four or more days may yield further insights into what constitutes more or less favorable mortality days but this is beyond the scope of the present paper. The data so far have dealt only with total CHD or stroke deaths. We are also interested in describing associations according to age and sex. Material similar to tables -6 was prepared separately for males, females, ages under 6 and ages 6 and over. A portion of these results those for the 7 snow areas is given in table 7. For CHD, the main pattern is seen to be essentially the same by sex and by age, although the excess for snowfall days compared with other cold days (A vs. B days) is more pronounced for males than females and for ages under 6 compared with ages 6 and over. For stroke deaths, table 7 shows that the largest excesses occur during the very hot E-days for all groups, with the excess more pronounced for females than males, and for the 6+ ages compared with those under 6. Unlike CHD, there is no observed excess for snowfall days compared with other cold days (A vs. B days) for males, although a substantial difference is noted for females. The main results described above for temperature and snowfall were examined separately by year for the larger areas and appeared to be consistent from year to year. TABLE 7 Average index numbers for CHD and stroke deaths by weather on day of death and sex, and by weather on day of death and age (in years)- 7 SMSA's, US, -6 Average temperature and enow- fall on day ofdeath* Male Female CHD <66 6+ Male Female Stroke <6 6+ A B C D E t f 0 09* 06 0 * See table for list of areas, description of weather categories and average index numbers, t Based on areas. X Based on 9 areas.

10 7 ROGOT AND PADGETT DISCUSSION Of the several results in this study, the most important we believe is the inverse relationship between temperature and mortality which prevails over most of the temperature range. The idea that extremely cold weather has an adverse effect upon people, sick or well, is easily appreciated. Many studies have in fact shown that excess mortality occurs when the weather is very cold. Not so evident and certainly not as well known is the greater mortality occurring at the more moderate temperatures of 0-9 F (.-9.9 C) compared with 0-9 F (0.0-. C), or that of 0-9 F compared with F (.6-.0 C). Further, this inverse relationship is remarkably consistent from area to area. The main differences between areas seem to be the exact temperature grouping at which mortality is lowest, and whether in fact an upturn in mortality is realized at the very high temperatures. The fact that the "ideal" temperature is somewhat higher for the warmer areas seems reasonable. This suggests that a relative as well as an absolute level of temperature is important, and that an overall physiologic adjustment or adjustment in life style to the local climate occurs. In theory, the relationship between mortality and temperature might be visualized as a U-shaped function with mortality rising very sharply during extremely cold and extremely hot weather. A hint of this is present mainly for some of the colder areas for CHD. The fact that stroke deaths do not show any consistent pattern at the colder temperatures is not understood. One possibility may be that with stroke, since there is on the average a longer period between onset and death than with CHD, and since there are relatively few days at the coldest temperatures, there may be a masking of the underlying effect as a given stroke death may be associated with the temperature of a day several removed from the day of onset. If the day of onset were in the coldest temperature grouping, the day of death could easily fall into a higher temperature grouping. This would be less apt to happen for CHD since a high proportion of CHD deaths are "sudden," occurring within one hour of onset (). We also have the prolonged effects of snowfall upon stroke deaths which may confuse the picture. The excess of CHD mortality associated with snowfall was anticipated. The results agree with previous findings reported for Chicago for 7 (6, 7) and with a recent Japanese report (9) on hospitalized cases of myocardial infarction. As far as we know there is no other literature on this subject. The finding of excess mortality from stroke associated with snowfall was unexpected. Yet more surprising was the finding that overall, the per cent excess for stroke was greater than that observed for CHD. However, CHD mortality was much more strongly related to amount of snow than was stroke. This suggests that factors associated with snow rather than snow itself may be responsible for the increase in stroke mortality during the snow period. There is a widespread clinical impression that shoveling snow may set off a heart attack. We know of no similar claim for stroke. In any event, this study provides no data bearing directly on these points. An interesting finding worth noting in the present study is the apparent cumulative effect of the very hot days upon mortality, in most of the colder areas and in Los Angeles and San Diego. Thus, for example, average index numbers for CHD over the 7 snow areas were 0, 0 and and for stroke, and 3 for DDE, DEE and EEE-days, respectively (table 6). The question arises, "For how many days does a cumulative effect persist?" A full study of this question is beyond the scope of the present study. A special study of New York and Chicago in

11 WEATHER AND CORONARY AND STROKE MORTALITY 7 this respect showed that the excess mortality built up for about a week and then declined. The ideal temperature of F ( C), at which lowest mortality generally occurs, corresponds with what many people consider to be pleasant temperatures. Possibly such days are considered pleasant because the cardiovascular system is functioning at its optimum. Evidently, any departure from an "ideal day" constitutes a threat sufficient in some instances to kill. Some of the observed excesses in mortality are no doubt due to terminal or very seriously ill heart or stroke patients succumbing in bad weather, the so called "harvesting effect." However, there may also be a concomitant increase in incidence of disease, and in severity of disease, as well. These increases must also contribute to the observed excess mortality in bad weather. In support of this we have a number of studies in which hospital admissions were related to the weather or season of the year: for example, the studies of Rose (7), Bull (), Doring and Loddenkemper (0) oryamazaki (9). We visualize a simple process in which bad weather, defined as average daily temperature outside the ideal range, exerts an adverse effect upon everyone whether healthy or sick. In the case of CHD, new disease may develop and result in sudden death that day, in death the next day or several days later. An increase in severity of disease could also occur and result in death that day or in the next several days. Such events could be directly attributable to the weather. In the case of stroke, a similar situation may prevail but with relatively fewer sudden deaths and relatively more prolonged effects due to the weather. REFERENCES. Jones WHS: Translation of Hippocrates' Air, Waters and Places. London, Heineman, 93. Justin MN: The effect of weather on health as shown by a study of the mortality statistics of New York City for the years 3-. Unpublished doctoral dissertation. New Haven, Yale University, Huntington E: Weather and Health: a study of daily mortality in New York City. National Research Council Bulletin No 7, Washington DC, The Council, 0. Rosenwaike I: Seasonal variation of deaths in the United States, -0. J Am Stat Assoc 6:706-79, 6. Rogot E, Fabsitz R, Feinleib M. Daily variation in USA mortality. Am J Epidemiol 03:-, 6 6. Boyd JT: Climate, air pollution, and mortality. Br J Prev Soc Med.3-3, 0 7. Rose G: Cold weather and ischaemic heart disease. Br J Prev Soc Med 0:-, 6. Bull GM: Meteorological correlates with myocardial and cerebral infarction and respiratory disease. Br J Prev Soc Med 7:0-3, May 3 9. Baubinene A: The seasonal fluctuation of myocardial infarction and the time of its onset. Kardiologiia 6:6-70, 6 0. Doring H, Loddenkemper R: Statistical investigations of myocardial infarction Z Kreislaufforsch :0-,. Momiyama M, Katayama K- Deseasonalization of mortality in the world. Int J Biometeorol 6:39-3,. Heyer HE, Teng HC, Bams W: The increased frequency of acute myocardial infarction during summer months in a warm climate; a study of,36 cases from Dallas, Texas. Am Heart J :7-7, 3. DePasquale NP, Burch GE: The seasonal incidence of myocardial infarction in New Orleans. Am J Med Sci 0,,,. Avierinos C: Seasonal incidence of acute myocardial infarction in Egypt in relation to the climate. Arch Mai Coeur.76-7,. Rogot E, Blackwelder WC: Associations of cardiovascular mortality with weather in Memphis, Tennessee. Public Health Rep.-39, 0 6. Rogot E: Association of cardiovascular mortality with weather Chicago, 7. In Air Conditioning, Climatology and Health. Presented at the meeting of the American Society of Heating, Refrigerating and Air Conditioning Engineers in Washington DC, New York, ASHRAE, 3, pp Rogot E: Associations between coronary mortality and the weather, Chicago, 7. Public Health Rep 9:330-33,. Moriyama IM, Krueger DE, Stamler J: Cardiovascular diseases in the United States. Cambridge, Harvard University Press,, p 0 9. Yamazaki N: Effects of hereditary and environmental factors on development of myocardial infarction. Jap Circ J 37: 69-77, 3