Retrospective Cohort Mortality Study Research Articles

Retrospective cohort mortality study of workers with potential exposure to epichlorohydrin and allyl chloride

Previous epidemiologic research has associated potential epichlorohydrin exposure with lung cancer and, in conjunction with allyl chloride exposure, to heart disease mortality. The study was designed to test both hypotheses by examining the mortality experience of 1,064 male employees (12,574 person-years) who had a minimum of 1 month work experience between 1957-1986 in the production or use of epichlorohydrin and allyl chloride and 1 year total employment duration at Dow Chemical's Texas Operations. Vital status follow-up occurred through 1989 of which there were 66 total deaths (standardized mortality ratio [SMR] = 80, 95% confidence interval [CI] 62-101). There were no significantly elevated SMRs for all malignant neoplasms, lung cancer, circulatory system disease, or arteriosclerotic heart disease when compared to external (U.S.) or internal (Texas Operations) populations. There were no apparent mortality trends with cumulative exposure analyses of potential epichlorohydrin exposure with and without accompanying allyl chloride exposure. A high prevalence of circulatory system death certificates were certified by nonphysicians in the local county and more than one third were described in nonspecific terms. The study results are not consistent with the prior hypothesized associations. However, the study results are limited by the cohort's size, duration of follow-up, relatively few number of observed and expected deaths, and the level of potential epichlorohydrin exposure experience.

Mortality of workers employed in shoe manufacturing.

A retrospective cohort mortality study was conducted among 7814 white shoe manufacturing workers followed from 1940 through 1982. The workers were potentially exposed to solvents (including toluene) and solvent-based adhesives. Benzene may have been present as an impurity of toluene. Mortality due to leukemia and aleukemia was not statistically significantly elevated. Statistically significant excess mortality due to cancer of the trachea, bronchus and lung was observed in the total cohort [standardized mortality ratio (SMR) 147, 95% confidence interval (95% CI) 120-180] and showed a statistically significant trend in standardized relative risk with increasing potential latency, but not with increasing duration of employment. Chronic nonmalignant respiratory disease was significantly elevated among the men (SMR 158, 95% CI 114-217) but was less than expected among the women (SMR 79), a finding suggesting a possible contribution of smoking to the mortality from respiratory cancer. However, adjustment for the potential effects of smoking did not completely eliminate the increased risk for lung cancer.

Notification of workers about an excess of malignant melanoma: A case study

In January 1991, NIOSH completed a retrospective cohort mortality study of 3,588 Westinghouse Electric Corporation workers who had been engaged in the manufacture of electrical capacitors. The study evolved from a NIOSH Health Hazard Evaluation, which was conducted at the request of the Indiana State Board of Health because of its concern about PCB exposures among the Westinghouse workers. Life table analysis revealed a fourfold excess of deaths due to malignant melanoma. Though the workers were principally exposed to PCBs, the available exposure data did not lend itself to constructing an exposure-response curve that could relate PCB exposure to development of malignant melanomas. This was further complicated by the lack of substantial corroboration from other studies of PCB-exposed cohorts. Because of the magnitude of the malignant melanoma excess and the fact that malignant melanoma is probably more amenable to treatment and remediation than most other cancers, NIOSH determined that notification of the individual cohort members was a prudent and necessary public health action. This article describes the notification process from the time the decision to notify was made through the postnotification period. It details the interaction between NIOSH, the former and current plant owners, the two labor organizations that represented the workers at the plant, and the recipients of the notification materials. Scientific and other issues surrounding this notification effort are also discussed. A number of lessons were learned about the notification process; these are described for the benefit of others who conduct notifications.

Renal cell cancer among paperboard printing workers.

A physician's alert prompted us to investigate workers' cancer risk at a paperboard printing manufacturer. We conducted a retrospective cohort mortality study of all 2,050 persons who had worked at the facility for more than 1 day, calculated standardized incidence ratios (SIRs) for bladder and renal cell cancer, and conducted a nested case-control study for renal cell cancer. Standardized mortality ratios (SMRs) from all causes [SMR = 1.0, 95% confidence interval (CI) = 0.9-1.2] and all cancers (SMR = 0.6, 95% CI = 0.3-1.0) were not greater than expected. One bladder cancer and one renal cell cancer were included in the mortality analysis. Six incident renal cell cancers were observed, however, compared with less than two renal cell cancers expected (SIR = 3.7, 95% CI = 1.4-8.1). Based on a nested case-control analysis, the risk of renal cell cancer was associated with overall length of employment but was not limited to any single department or work process. Although pigments containing congeners of dichlorobenzidine and o-toluidine had been used at the plant, environmental sampling could not confirm any current exposure. Several limitations and a potential selection bias limit the inferences that can be drawn.

Colon and Stomach Cancer Mortality among Automotive Wood Model Makers

Automotive wood model makers have been reported to be at excess risk for colon and other cancers in recent epidemiologic studies. To further explore these risks, we conducted a retrospective cohort mortality study, with follow-up from 1940 through 1984, of 2294 white male wood model makers employed at any time until 1980 by three US auto makers. Using US mortality rates for comparison, we found elevated standardized mortality ratios of 1.2 (95% CI, 0.8-1.9) for colon cancer and 1.6 (95% CI, 0.9-2.6) for stomach cancer. We also conducted nested case-control studies for 20 colon and 17 stomach cancer cases and 543 age-matched controls. We found no trend of increased risk for colon or stomach cancer mortality with increased exposure to wood dust or to duration employed in wood model making.

A dose-response analysis and quantitative assessment of lung cancer risk and occupational cadmium exposure.

We performed a quantitative assessment of the risk of lung cancer from exposure to cadmium based on a retrospective cohort mortality study of cadmium-exposed workers. The study population consisted of white male workers who were employed for at least 6 months at a cadmium smelter between January 1, 1940, and December 31, 1969, and who were first employed at the facility on or after January 1, 1926. The study findings were analyzed using a modified life-table analysis to estimate standardized mortality ratios (SMRs), and various functional forms (i.e., exponential, power, additive relative rate, and linear) of Poisson and Cox proportional hazards models to examine the dose-response relationship. Estimates of working lifetime risk (45 years) were developed using an approach that corrects for competing causes of death. An excess in mortality from lung cancer was observed for the entire cohort (SMR = 149, 95% confidence interval (CI) = 95, 222). Mortality from lung cancer was greatest among non-Hispanic workers (SMR = 211, 95% CI = 131, 323), among workers in the highest cadmium exposure group (SMR = 272, 95% CI = 123, 513), and among workers with 20 or more years since the first exposure (SMR = 161, 95% CI = 100, 248). A statistically significant dose-response relationship was evident in nearly all of the regression models evaluated. Based on our analyses, the lifetime excess lung cancer risk at the current Occupational Safety and Health Administration standard for cadmium fumes of 100 micrograms/m3 is approximately 50 to 111 lung cancer deaths per 1000 workers exposed to cadmium for 45 years.

Cardiovascular mortality among munitions workers exposed to nitroglycerin and dinitrotoluene.

A retrospective cohort mortality study with 5529 nitroglycerin, 4989 dinitrotoluene, and 5136 unexposed workers compared the mortality of the exposed groups with that of the United States population and that of the unexposed group with life-table analysis and Poisson regression. Mortality from ischemic heart disease was close to that expected, and mortality from cerebrovascular disease was slightly less than that expected, for the workers with both nitroglycerin and dinitrotoluene exposure and for those with dinitrotoluene exposure only. A significant interaction between age and nitroglycerin exposure was detected in the Poisson regression analyses for ischemic heart disease, particularly for workers actively exposed to nitroglycerin. The rate ratio for the workers under 45 years of age and actively exposed to nitroglycerin was 3.30 (95% confidence interval 129-8.48). This study did not show a chronic effect of nitroglycerin or dinitrotoluene exposure on cardiovascular disease risk. Potential biases related to the company's medical screening program may have limited the ability to detect chronic cardiovascular effects.

A mortality study of workers at seven beryllium processing plants.

The International Agency for Research on Cancer (IARC) has found that the evidence for the carcinogenicity of beryllium is sufficient based on animal data but "limited" based on human data. This analysis reports on a retrospective cohort mortality study among 9,225 male workers employed at seven beryllium processing facilities for at least 2 days between January 1, 1940, and December 31, 1969. Vital status was ascertained through December 31, 1988. The standardized mortality ratio (SMR) for lung cancer in the total cohort was 1.26 (95% confidence interval [CI] = 1.12-1.42); significant SMRs for lung cancer were observed for two of the oldest plants located in Lorain, Ohio (SMR = 1.69; 95% CI = 1.28-2.19) and Reading, Pennsylvania (SMR = 1.24; 95% CI = 1.03-1.48). For the overall cohort, significantly elevated SMRs were found for "all deaths" (SMR = 1.05; 95% CI = 1.01-1.08), "ischemic heart disease" (SMR = 1.08; 95% CI = 1.01-1.14), "pneumoconiosis and other respiratory diseases" (SMR = 1.48; 95% CI = 1.21-1.80), and "chronic and unspecified nephritis, renal failure, and other renal sclerosis" (SMR = 1.49; 95% CI = 1.00-2.12). Lung cancer SMRs did not increase with longer duration of employment, but did increase with longer latency (time since first exposure). Lung cancer was particularly elevated (SMR = 3.33; 95% CI = 1.66-5.95) among workers at the Lorain plant with a history of (primarily) acute beryllium disease, which is associated with very high beryllium exposure. The lung cancer excess was not restricted to plants operating in the 1940s, when beryllium exposures were known to be extraordinarily high. Elevated lung cancer SMRs were also observed for four of the five plants operating in the 1950s for workers hired during that decade. Neither smoking nor geographic location fully explains the increased lung cancer risk. Occupational exposure to beryllium compounds is the most plausible explanation for the increased risk of lung cancer observed in this study. Continued mortality follow-up of this cohort will provide a more definitive assessment of lung cancer risk at the newer plants and among cohort members hired in the 1950s or later at the older plants. Further clarification of the potential for specific beryllium compounds to induce lung cancer in humans, and the possible contribution of other exposures in specific processes at these plants, would require a nested case-control study. We are currently assessing whether available industrial hygiene data would support such an analysis.

Mortality among Women Vietnam Veterans, 1973–1987

A retrospective cohort mortality study was conducted to examine health effects of US military service in Vietnam on women veterans who served there between July 4, 1965 and March 28, 1973. About 4,600 women Vietnam veterans and 5,300 women veterans who had never served in Vietnam were identified from military records and followed for vital status on December 31, 1987. Mortality rates for all causes of death combined and for all cancers among Vietnam veterans were similar to those among non-Vietnam veterans (relative risk (RR) = 0.93). There was a slight excess of mortality from external causes among women Vietnam veterans compared with non-Vietnam veterans (RR = 1.33), primarily due to an excess of motor vehicle accidents (RR = 3.19). Suicide rates were nearly the same in both cohorts (RR = 0.96). Vietnam veterans had twofold increases in mortality from cancers of the pancreas and uterine corpus compared with non-Vietnam veterans. Women Vietnam veterans and non-Vietnam veterans had lower-than-expected mortality from all causes of death combined (standardized mortality ratio (SMR) = 0.82 and 0.88, respectively), based on rates for US women, due to significant deficits of deaths from circulatory diseases. Compared with rates for US women, mortality from cancers of the pancreas (five deaths, SMR = 3.27) and uterine corpus (four deaths, SMR = 4.05) was significantly elevated among Vietnam veteran nurses.

Retrospective cohort mortality study of workers at an aircraft maintenance facility. I. Epidemiological results.

A retrospective cohort study of 14,457 workers at an aircraft maintenance facility was undertaken to evaluate mortality associated with exposures in their workplace. The purpose was to determine whether working with solvents, particularly trichloroethylene, posed any excess risk of mortality. The study group consisted of all civilian employees who worked for at least one year at Hill Air Force Base, Utah, between 1 January 1952 and 31 December 1956. Work histories were obtained from records at the National Personnel Records Centre, St. Louis, Missouri, and the cohort was followed up for ascertainment of vital state until 31 December 1982. Observed deaths among white people were compared with the expected number of deaths, based on the Utah white population, and adjusted for age, sex, and calendar period. Significant deficits occurred for mortality from all causes (SMR 92, 95% confidence interval (95% CI) 90-95), all malignant neoplasms (SMR 90, 95% CI 83-97), ischaemic heart disease (SMR 93, 95% CI 88-98), non-malignant respiratory disease (SMR 87, 95% CI 76-98), and accidents (SMR 61, 95% CI 52-70). Mortality was raised for multiple myeloma (MM) in white women (SMR 236, 95% CI 87-514), non-Hodgkin's lymphoma (NHL) in white women (SMR 212, 95% CI 102-390), and cancer of the biliary passages and liver in white men dying after 1980 (SMR 358, 95% CI 116-836). Detailed analysis of the 6929 employees occupationally exposed to trichloroethylene, the most widely used solvent at the base during the 1950s and 1960s, did not show any significant or persuasive association between several measures of exposure to trichloroethylene and any excess of cancer. Women employed in departments in which fabric cleaning and parachute repair operations were performed had more deaths than expected from MM and NHL. The inconsistent mortality patterns by sex, multiple and overlapping exposures, and small numbers made it difficult to ascribe these excesses to any particular substance. Hypothesis generating results are presented by a variety of exposures for causes of death not showing excesses in the overall cohort.

Retrospective cohort mortality study of workers at an aircraft maintenance facility. II. Exposures and their assessment.

Methods are presented that were used for assessing exposures in a cohort mortality study of 15,000 employees who held 150,000 jobs at an Air Force base from 1939 to 1982. Standardisation of the word order and spelling of the job titles identified 43,000 unique job title organisation combinations. Walkthrough surveys were conducted, long term employees were interviewed, and available industrial hygiene data were collected to evaluate historic exposures. Because of difficulties linking air monitoring data and use of specific chemicals to the departments identified in the work histories, position descriptions were used to identify the tasks in each job. From knowledge of the tasks and the chemicals used in those tasks the presence or absence of 23 chemicals or groups of chemicals were designated for each job organisation combination. Also, estimates of levels of exposure were made for trichloroethylene and for mixed solvents, a category comprising several solvents including trichloroethylene, Stoddard solvent, carbon tetrachloride, JP4 gasoline, freon, alcohols, 1,1,1-trichloroethane, acetone, toluene, methyl ethyl ketone, methylene chloride, o-dichlorobenzene, perchloroethylene, chloroform, styrene, and xylene.

A retrospective cohort mortality study of blending and packaging workers of mobil corporation

This retrospective cohort mortality study examined 2,467 workers in lubrication products blending and packaging (B&P) operations at two refineries of Mobil Corporation between January 1, 1945 and December 31, 1978. Ninety-seven percent were male. Compared with U.S. males, there were significantly fewer deaths observed among males due to all causes, external causes, and diseases of the circulatory, respiratory, digestive, and genitourinary systems. Deaths observed from all cancer were fewer than expected, although not statistically significant. No statistically significant excess cause-specific mortality occurred at B&P facilities combined or separately. Nonsignificant increases in mortality were observed for cancers of the stomach, large intestine, prostate, the category of "other lymphatic tissue" cancer, and leukemia and aleukemia. Analyses demonstrated a statistically significant pattern of increasing SMR with employment duration for "other lymphatic tissue" cancer. Within the highest cumulative duration of employment category, the excess was confined to workers after 30 or more years since first employment. Although the interpretation of cancer mortality patterns is limited due to small numbers of deaths, the absence of associations with specific B&P departments is evidence against a causal interpretation.

Retrospective cohort mortality study of cancer among sewage plant workers

There is little known about the incidence of cancer among sewage workers. In this paper we examine findings from a retrospective cohort study of 487 white male sewer authority workers employed between January 1950 and October 1979. Vital status was ascertained for 93% of the cohort yielding a total of 6,886 person years. Total mortality from all causes was comparable to that of the general white male U.S. population (Standardized Mortality Ratio [SMR] = 0.91, 95% Confidence Interval [CI] = 0.77-1.07). The cohort was subdivided into those not exposed, and sewer workers who were exposed to sewage effluent, sludge, or wastewater containing chemicals including potential carcinogens. Among the nonexposed group, mortality from all causes was significantly low (SMR = 0.55, 95% CI = 0.33-0.88). Among the exposed sewer workers, mortality from all causes was not significantly different from that of the general white male U.S. population (SMR = 1.00, 95% CI = 0.84-1.19). Mortality from all cancers among exposed sewer workers was slightly higher than that of the general population (SMR = 1.19, 95% CI = 0.79-1.7). Statistically significant elevated mortality ratios were seen for cancer of the larynx (SMR = 7.93, 95% CI = 1.59-23.96), and cancer of the liver (SMR = 5.4, 95% CI = 1.10-16.05). Careful study of the medical and occupational histories of these cases suggested that larynx cancer was possibly work-related, while liver cancer was not. A group estimated to be the highest exposed, composed predominantly of operatives, had a higher directly adjusted death rate from all malignant neoplasms combined compared to all other workers (rate ratio = 1.64). These findings of increased risk of cancer among exposed sewage workers, especially operators, are based on small number of cases and should be interpreted with caution. Studies of larger cohorts are needed to clarify the risk of these cancers among sewage workers.

Respiratory mortality among firefighters.

Although firefighters have been shown in some studies to suffer chronic respiratory morbidity from their occupational exposures, an increased risk for dying from non-malignant respiratory diseases has not been documented in any previous retrospective cohort mortality study. In order to assess the possibility that an unusually strong "healthy worker effect" among firefighters might mask this increased risk, a mortality analysis of firefighters was carried out in three cities in relation to the United States population and also to a comparison cohort of police officers. The firefighters were employed between 1945 and 1980 and experienced 886 deaths by 1 January 1984; compared with the United States population they had a significantly reduced risk of dying from all causes (SMR = 82, 95% confidence interval, 77-87), and from non-malignant circulatory diseases (SMR = 81, 95% confidence interval 73-89), but no significant difference in risk of non-malignant respiratory diseases (SMR = 88, 95% confidence interval 66-117). Compared with police, the firefighters experienced a trend toward improved mortality outcomes for all causes investigated (SMR = 82), but they had an excess of deaths from non-malignant respiratory diseases (SMR = 141). The results indicate that firefighters are probably at increased risk for dying from non-malignant respiratory diseases; this increased risk may have been missed in previous studies because of the limitations of using a general reference population.

Mortality of Iron Foundry Workers: I. Overall Findings

A retrospective cohort mortality study was conducted among 8147 men and 627 women employed in a gray iron foundry for at least 6 months between 1950 and 1979. More than 1700 deaths occurred during a 35-year period of observation. Standardized mortality ratios (SMRs) for all causes were close to expected values based on the US general population as the standard. The mortality of nonwhite men was significantly increased for lung cancer (SMR 132) and ischemic heart disease (SMR 126). Other moderate, but nonsignificant excesses were noted among nonwhite men for cancers of the stomach, pancreas, and prostate, for diabetes mellitus and pulmonary emphysema, and among white men for cancers of the lung and stomach, gastric and duodenal ulcers, pulmonary emphysema, and suicide. Small mortality increases were observed in both racial groups for cerebrovascular disease. The lack of a trend with time since hire and duration of foundry employment suggests that lung cancer mortality may not be associated with exposure to the foundry environment. Utilizing indirect measures of smoking, it appears that virtually all excess lung cancer deaths among whites and at least some of the excess among nonwhites could be explained by smoking habits. Similarly, smoking may have been responsible for the mortality excesses from emphysema, cerebrovascular diseases, and ischemic heart disease.

Environmental epidemiologic investigations in the styrene-butadiene rubber production industry.

A review of the literature and an update that is in progress of a previous retrospective cohort mortality study of the styrene-1,3-butadiene industry are discussed. The follow-up has now been extended from April 1, 1976, through December 31, 1981, for plant B and December 31, 1982, for plant A. The person-years at risk of death have gone from 34,187 to 43,341 in plant A and from 19,742 to 26,314 in plant B. Among the death certificates received to date, observed deaths have increased in both plants, with increases in cancers of the trachea, bronchus and lung and in lymphosarcomas, reticulosarcomas, and cancers of the overall lymphatic and hematopoietic system.

Retrospective Cohort Mortality Study of Roman Catholic Priests

In order to test the hypothesis that Roman Catholic priests are at low risk for prostatic cancer because of their celibacy, a cohort of 10,026 men who were active or retired diocesan (parish) Roman Catholic priests in the United States on January 1, 1949 were followed until death, leaving the priesthood, or January 1, 1978. The overall standardized mortality ratio (SMR) was 103 and the SMR for cancer of the prostate was 81. Other interesting findings include increased SMRs for cancer of the larynx (147), cirrhosis of the liver (147), and diabetes (182) and decreased SMRs for lung cancer (59), emphysema (26), and suicide (13).

A retrospective cohort mortality study on workers of two thermoelectric power plants: fourteen-year follow-up results.

Although many studies have been performed to evaluate the environmental impact of coal energy production, few studies are available on the health risk for the people working in coal power plants. A retrospective cohort study was performed on the workers of two power plants near Venice (which use coal since 1968) in order to test the association between exposure to coal dust and ashes and mortality for all causes, all cancers, and respiratory and digestive cancer. One thousand three hundred seven male workers were followed up from 1968 to 1984. During this period 41 workers died; causes of death were collected from the local Mortality Registers and/or from the Hospital Records. The observed mortality of the study cohort was compared with the mortality expected from the Italian death rates in the same period. No Standardized Mortality Ratio (SMR) was found in excess in the working cohort with respect to the standard population for any of the investigated effects.

Retrospective cohort mortality study of Roman Catholic Priests

In order to test the hypothesis that Roman Catholic priests are at low risk for prostatic cancer because of their celibacy, a cohort of 10,026 men who were active or retired diocesan (parish) Roman Catholic priests in the United States on January 1, 1949 were followed until death, leaving the priesthood, or January 1, 1978. The overall standardized mortality ratio (SMR) was 103 and the SMR for cancer of the prostate was 81. Other interesting findings include increased SMRs for cancer of the larynx (147), cirrhosis of the liver (147), and diabetes (182) and decreased SMRs for lung cancer (59), emphysema (26), and suicide (13).

Mortality among workers at a nuclear fuels production facility.

A retrospective cohort mortality study was conducted in a population of workers employed at a facility with the primary task of production of nuclear fuels and other materials. Data for hourly and salaried employees were analyzed separately by time period of first employment and length of employment. The hourly (N = 6,687 with 728 deaths) and salaried (N = 2,745 with 294 deaths) employees had a mortality experience comparable to that of the United States and, in fact, exhibited significant fewer deaths in many categories of diseases that are traditionally associated with the healthy worker effect. Specifically, fewer deaths were noted in the categories of all causes, all cancers, cancer of the digestive organs, lung cancer, brain cancer (hourly workers only), diabetes, all diseases of the circulatory system, all respiratory diseases, all digestive system diseases, all diseases of the genitourinary system (hourly only), and all external causes of death. A statistically significant, and as yet unexplained increase in leukemia mortality (6 observed vs. 2.18 expected) appeared among a subset of the hourly employees, first hired before 1955, and employed between 5-15 years.