Document Ra4499O9Z9Bw3qg0OxMyZqNba

M SIA 6- ntM-2 STUDY OF MYOCARDIAL INFARCTION AT WASHINGTON WORKS PLANT This study was conducted to evaluate the incidence of cases of myocardial infarction among male wage and salary roll employees at the Washington Works Plant from 1956 to 1973. Dr. Y. 1 Power, Plant Physician, requested the investigation because some workers had complained that the occurrence of heart attacks among employees seemed excessive. DESIGN AND METHODS A computer search of the morbidity files in Wilmington produced a list of cases for this retrospective study. A case is defined as any male employee who suffered a first myocardial in farction (M.I.) between January 1, 1956, and December 31, 1973. This definition includes persons who recovered from an acute M.I. and those who died suddenly from coronary heart disease. Persons who had left work for any reason were considered potential propositi during only those years in the study period when they were active employees. Females were excluded from .the study, as they represent a group too small in size for statistical analysis. Additional data concerning plant population statistics and occupational profiles for each case were obtained from records at Washington Works. AC Sixty-one cases of M.I. were observed during the eighteen- year period. A breakdown by age categorization within three-year periods for salary roll and for wage roll men is presented in Table I. 2 Age-specific Du Pont Company rates for male wage roll and salaried personnel were used to compute the expected number of M.I.'s at Washington Works. Again, three-year time periods were selected for this determination. It would not have been sufficient to have referred to the 1973 figures, nor to have averaged or otherwise aggregated the rates over the eighteen years, because a trend toward lower incidence in the Du Pont Company has occurred in recent years. The Company rates are shown in Table II. The observed number of myocardial infarctions at Washington Works and the number of cases predicted according to Company statistics are presented in Table III for wage roll and for salary roll employees. ANALYSIS No excess incidence of M.I. is evident among the male wage roll employees. The expected number of M.I.'s is 34.0? 32 were observed. One notices that the number of cases has been in creasing over the years at Washington Works. One suggested explana tion is that with an increasing percentage of employees over the age of fifty, both at Washington Works Plant and in the Company (Table IV), more M.I.'s are to be expected. Among salaried employees, the observed incidence of myocardial infarction is significantly higher than the expected number, under the assumption that cases follow a Poisson distri bution: 1 .1s were observed? 23_ 5 is the expected number I (P .06). The high overall incidence is largely the. result of elevated rates in recent years. In.the period from 1971 to 1973, the difference between observed and predictednumbers is great: EID713128 000091 3 12 observed cases versus 5.3 expected cases (P = 0.008) whereas in the preceeding years no differences between observed and ex pected numbers were significant. (P > .10 for all comparisons). Further investigation of occupation reveals that,the high frequency of M.I. cases among salaried employees is seen largely in foremen. Twenty of the twenty-nine cases occurred among the population of foremen at Washington Works: 8 were mechanical foremen, 9 were production foremen, 2 were laboratory foremen, and 1 was a yard and transportation foreman. Approximately thirty-five percent of the salaried men at the plant are foremen. Since the age distribution of foremen is comparable to that of all salaried employees at Washington Works, one would expect that only 10 of the observed M.I.'s would present in this occupational class {35% of 29),, compared to the 20 which occurred among foremen. The foremen studied range in age at onset of the attack from 35 to 65 years. Both the mean and the median number of years of experience as foremen prior to M.I. is 9.0. The range is 1 week to 25 years. Patrolmen, a group representing three percent of the Washington Works population, also showed a somewhat'elevated in cidence of M.I. Four cases were observed among patrolmen, whereas the expected number i s *1.4 (3% of 29). The age at onset for these patrolmen, however, ranges from 55-59 years; this-irs older than the median age at onset for the entire group, which is about 50 years. This consideration explains the increased incidence among patrolmen. Distribution of M.I. cases among employee work classifications is presented in Table V. 000092 4 : SUMMARY This study examines incidence of myocardial infarction among male employees at Washington Works over an eighteen-year period. Using Du Pont Company rates as the referrent, it was found that no excess of M.I. cases occurred among wage roll persons, whereas among salaried men, elevated morbidity rates obtain. The target group among salaried employees is foremen. Increased inci dence in this group cannot be explained by their age distribution. One asks, then, if some aspect of the work routine is a causal link in the development of coronary heart disease, or if some personal characteristic which predisposes one to become a foreman is a risk indicator for M.I. As a result of the findings of this study, tl Biostatistics Group in Wilmington will explore the possibility oj a Company-wide investigation of morbidity among foremen. f MAUREEN T. O'BERG Biostabistician 000093 TABLE I AGE DISTRIBUTION OF M.I. CASES BY THREE-YEAR PERIODS AT WASHINGTON WORKS, 1956-1973 Age__ 20 20-24 25-29 30-34 35-39 40-44 45-49 50-54 55-59 60-64 1956-58 1 Male Wage (Number of Employees) 1959-61 1962-64 1965-67 1968-70 . 1 2 23 21 1 12 3 1 31 . _ 1. 1971-73 1 1 3 2 Total 0 1 0 2 6 3 8 6 4 2 Total 1 6 4 6 8 7 32 Age 1956-58 20 20-24 25-29 30-34 35-39 40-44 45-49 50-54 55-59 50-- 64 : *','` Total 0 Male Salary (Number of Employees) 1959-61 1962-64 1965-67 1968-70 -- 1 1 .. 1 32 1 1. 2; 1 1 11 1 5 34 5 1971-73 2 1 2 7` Total 0 0 0 1 1 3 6~ 7' 10 1 12 29 00O J TABLE II Age-Specific Du Pont Company Rates, Per 100,000, of MI Cases Age 20 20-24 25-29 30-34 35-39 40-44 45-49 50-54 55-59 60-64 TOTAL 1956-58 0.0 0.0 4. 0 18.6 88.7 178.2 484.7 707.9 883.3 940.8 280 1959-61 0,0 0.0 0.0 21.3 117.7 282.7 384.0 812.1 962.5 910.3 357 WAGE - MEN 1962-64 1965-67 0.0 0.0 6.0 34.4 114.6 254.9 358.4 630.7 713.8 857.4 259 0.0 5.1 4.2 10.6 55.8 191.2 385.4 674.4 895.9 989.7 267 1968-70 0.0 12.4 11.7 15.8 111. 8 242.0 372. 9 565.3 919.6 1,064.9 275 1971-73 0.0 0.0 4.5 0.0 86.2 183. 6 422.5 648.2 804.4 1,169.8 271 Age 20 20-24 25-29 30-34 35-39 40-44 45-49 50-54 55-59 60-64 'TOTAL 1956-58 0.0 0.0 0.0 6.2 57.9 247.2 458.7 703.9 1,001.0 1,327.9 354 SALARY - MEN 1959-61 1962-64 1965-67 0.0 0.0 0.0 13.8 84. 0 184. 4 451.7 683.1 1,007.1 903.3 0.0 0.0 0.0 56.4 68.8 237.7 450.7 552.3 936.7 1,165.6 0.0 0. 0.0 8.3 119.9 175.2 342.7 645.5 849.8 1,024.2 330 331 303 1968-70 0.0 0.0 7.0 7.6 43.5 206.4 312.4 459.9 776.5 1,141.0 271 1971-73 0.0 0.0 0.0 20.5 64.9 180.0 343.4 476.2 707.0 972.5 215 *Age-adjusted rate EID713132 000095 TABLE I H OBSERVED NUMBER OF M.I. CASES AT WASHINGTON WORKS AND EXPECTED NUMBER OF M.I. CASES, BASED ON DU PONT COMPANY MORBIDITY Observed Expected 1956-58 1 2.2 1959-61 6 3.8 Male Wage 1962-64 1965-67 46 4.9 6.0 1968-70 8 8.2 1971-73 7 8.9 Tot 32 34. Observed Expected 1956-58 0, 1.5 1959-61 5 2.5 Male Salary 1962-64 1965-67 3^ 4 [0 3.5 3.9 1968-70 5 4.8 1971-73 Tota] 12 ){ 29 5.3 21.5 EID713133 000096 TABLE IV Age Categorization of Male Employees at Du Pont Company and Washington Works, 1956-1973 Age 50 _50 % > 50 1956-58 203,712 .44,287 18% DU PONT COMPANY WAGE AND SALARY COMBINED* 1959-61 1962-64 1965-67 181,142 49,733 22% 186,413 58,954 24% 205,110 67,960 25% 1968-70 197,957 72,259 27% 1971-73 183,441 . 74,020 29% Age 1956-58 50 > 50 % >. 50 3,136 151 4% WASHINGTON WORKS . WAGE AND SALARY COMBINED* 1959-61 1962-64 1965-67 1968-70 4,421 322 7% 4,712 526 10% 5,528 744 12% 6,370 1,000 14% 1971-73 6,031 1,225 17% *Each number represents the cumulative mid-year population for the three-year period. 000097 TABLE V OBSERVED NUMBER OF M.I. CASES BY OCCUPATION AND EXPECTED NUMBER OF M.I. CASES, BASED ON OCCUPATIONAL DISTRIBUTION AT WASHINGTON WORKS, MALE SALARIED EMPLOYEES % OF SALARIED OBSERVED EXPECTED EMPLOYEES AT NUMBER NUMBER OCCUPATION_______ WASHINGTON WORKS OF M.I. 'S OFM.I.'S* Foremen Supervision through Management 35% 23% 20 10.2 3 6.7 Specialists Analysts, Accountants Engineers Clerical Patrolmen Draftsmen TOTAL 2% 3% 22% 10% 3% 2% 1 1. 4 0 .9 0 6.4 0 2.9 4 .9 1 1.4 29 *expected Humber = % x 29 00009S