Retrospective Cohort Mortality Study Research Articles

A cohort mortality study of workers exposed to chlorinated organic solvents in Taiwan.

A retrospective cohort mortality study based on standardized mortality ratios (SMRs) was conducted to investigate the possible association between exposure to chlorinated organic solvents and various types of cancer deaths. Vital status and causes of death of study subjects were determined from January 1, 1985 to December 31, 1997 by linking cohort data with the National Mortality Database. Person-year accumulation began on the date of entry to the cohort, or January 1, 1985 (whichever came later), and ended on the closing date of the study (December 31, 1997), if alive; or the date of death. This retrospective cohort study examined cancer mortality among 86,868 workers at an electronics factory in the northern Taiwan. Using various durations of employment and latency and adjusting for age and calendar year, no significantly elevated SMR was found for any cancer in either male or female exposed workers when compared with the general Taiwanese population. In particular, the risk of female breast cancer was not found to be increased. Although ovarian cancer suggested an upward trend when analyzed by length of employment, ovarian cancer risk for the entire female cohort was not elevated. It is concluded that this study provided no evidence that exposure to chlorinated organic solvents was associated with human cancer risk.

A cohort mortality study among titanium dioxide manufacturing workers in the United States.

Although titanium dioxide (TiO2) is generally regarded as a nontoxic mild pulmonary irritant, some laboratory studies have reported lung adenomas in rats exposed to high levels of TiO2. Limited data on health effects among humans exist. A retrospective cohort mortality study was conducted among 4241 TiO2 workers who were employed for at least 6 months, on or after January 1, 1960, at four TiO2 plants in the United States. Exposure categories, defined by plant, job title, and calendar years in the job, were created to examine mortality patterns in those jobs where the potential for TiO2 exposure is greatest. Standardized mortality ratios (SMRs) and their 95% confidence intervals (CI) were calculated to compare the mortality pattern of the workers with the general background population. Relative risks were estimated and trend tests were conducted to examine risk of disease among different exposure level groups in internal analyses. Workers experienced a significantly low overall mortality (SMR = 0.8; 95% CI = 0.8-0.9). No significantly increased SMRs were found for any specific cause of death. Deaths from lung cancer were as expected, and SMRs for this cancer did not increase with increasing TiO2 levels. Workers in jobs with greatest TiO2 exposure had significantly fewer than expected total deaths (SMR = 0.7; 95% CI = 0.6-0.9). Internal analyses revealed no significant trends or exposure-risk associations for total cancers, lung cancer, or other causes of death. Results from our study indicate that the exposures at these United States plants are not associated with increases in the risk of death from cancer or other diseases. Moreover, workers with likely higher levels of TiO2 exposure had similar mortality patterns to those with less exposure, as internal analyses among workers revealed no increase in mortality by level of TiO2 exposure.

Asbestos related diseases from environmental exposure to crocidolite in Da-yao, China. I. Review of exposure and epidemiological data

Background: Scattered patches of crocidolite, one form of asbestos, were found in the surface soil in the rural county of Da-yao in southwestern China. In 1983, researchers from the West...

Assessment of Mortality in Patients Enrolled in a Risedronate Clinical Trial Program: A Retrospective Cohort Study

Risedronate, a pyridinyl bisphosphonate, has been shown in large clinical trials to be effective in the prevention and treatment of osteoporosis. Analysis of safety data from these trials has shown that risedronate (2.5- and 5-mg doses) has an overall safety profile comparable to placebo during the course of the clinical trials. The clinical trials were powered appropriately to analyze the efficacy endpoints; however, patients were not systematically followed after completion of the clinical trials and therefore vital status for most of the patient cohort after the cessation of the clinical trials was unknown. In order to investigate further the safety profile of risedronate observed in the clinical trials database, we conducted a retrospective cohort mortality study among 7981 patients comprising the intent-to-treat population in three North American risedronate osteoporosis trials. No difference in all cause mortality was observed in patients receiving risedronate treatment compared with patients receiving placebo. There were also no differences between these groups in mortality due to all cancers, lung cancer, and gastrointestinal tract cancer. A trend toward lower cardiovascular mortality was observed in the risedronate groups compared with placebo; this difference was largely due to a significant reduction in stroke mortality in the active treatment groups. Follow-up mortality data in this retrospective cohort study demonstrate that treatment with risedronate has no effect on overall mortality rates.

A retrospective cohort mortality study of Italian commercial airline cockpit crew and cabin attendants, 1965-96.

A retrospective cohort mortality study was conducted among Italian commercial flight personnel for the period 1965-1996. The cohort was composed of 3,022 male cockpit crew members and 3,418 male and 3,428 female cabin attendants. Cause-specific standardized mortality ratios (SMRs) and exact 95% confidence intervals (CIs) were calculated as estimates of the relative risk. Mortality from all cancers was less than expected for all categories (SMRs of 0.58 for male cockpit crew, 0.67 for male cabin attendants, and 0.90 for female cabin attendants). Among male flight personnel, the SMR for leukemia was somewhat elevated (SMR 1.73; 95% CI: 0.75-3.41) based on eight deaths, with a positive trend by length of employment (p = 0.046). Additionally, an excess of death by suicide was seen among female cabin attendants (SMR 3.38; 95% CI: 1.24-7.35). Other Italian studies of flight personnel are under way, including a detailed assessment of cosmic radiation exposure and investigations of non-radiation occupational risk factors and prevalence of nonfatal outcomes.

A Retrospective Cohort Mortality Study of Italian Commercial Airline Cockpit Crew and Cabin Attendants, 1965–96

A Retrospective Cohort Mortality Study of Italian Commercial Airline Cockpit Crew and Cabin Attendants, 1965–96

Cohort mortality study of Philadelphia firefighters.

Fire fighters are exposed to a wide variety of toxic chemicals. Previous studies have reported excess risk of some cancers but have been limited by small numbers or little information on employment characteristics. We conducted a retrospective cohort mortality study among 7,789 Philadelphia firefighters employed between 1925 and 1986. For each cause of death, the standardized mortality ratios (SMRs) and 95% confidence intervals were estimated. We also compared mortality among groups of firefighters defined by the estimated number of career runs and potential for diesel exposure. In comparison with U.S. white men, the firefighters had similar mortality from all causes of death combined (SMR = 0.96) and all cancers (SMR = 1.10). There were statistically significant deficits of deaths from nervous system diseases (SMR = 0.47), cerebrovascular diseases (SMR = 0.83), respiratory diseases (SMR = 0.67), genitourinary diseases (SMR = 0.54), all accidents (SMR = 0.72), and suicide (SMR = 0.66). Statistically significant excess risks were observed for colon cancer (SMR = 1.51) and ischemic heart disease (SMR = 1.09). The risks of mortality from colon cancer (SMR = 1.68), kidney cancer (SMR = 2.20), non-Hodgkin's lymphoma (SMR = 1.72), multiple myeloma (SMR = 2.31), and benign neoplasms (SMR = 2.54) were increased among firefighters with at least 20 years of service. Our study found no significant increase in overall mortality among Philadelphia firefighters. However, we observed increased mortality for cancers of the colon and kidney, non-Hodgkin's lymphoma and multiple myeloma. There was insufficient follow-up since the introduction of diesel equipment to adequately assess risk.

Mortality among aircraft manufacturing workers.

OBJECTIVES: To evaluate the risk of cancer and other diseases among workers engaged in aircraft manufacturing and potentially exposed to compounds containing chromate, trichloroethylene (TCE), perchloroethylene (PCE), and mixed solvents....

Mortality of a police cohort: 1950–1990

The authors conducted a retrospective cohort mortality study on police officers from 1950-2005.Standardized Mortality Ratio (SMR) analyses were conducted separately for white male (n=2761), black (n=286), and female (n=259) officers.Mortality from all causes of death combined for white male officers was significantly higher than expected (SMR=1.20; 95% confidence interval (CI) =1.14-1.26). Increased mortality was also seen for all malignant neoplasms combined (SMR=1.32; 1.19-1.46), all benign neoplasms combined (SMR=2.50; 1.08-4.93), and all diseases of the circulatory system combined (SMR=1.11; 1.02-1.19). The elevated mortality for all malignant neoplasms was primarily due to statistically significant excesses in cancers of the esophagus, colon, respiratory system, Hodgkin's disease and leukemia. Black officers had lower than expected mortality from all causes (SMR=0.45; 0.18-0.92) while female officers had elevated all-cause mortality (SMR=2.17; 1.12-3.79).Findings of increased risk for malignant neoplasms should be replicated and studied in relation to measured risk factors.

Mortality of a police cohort: 1950-1990.

This study presents findings from an updated retrospective cohort mortality study of male police officers from January 1, 1950 to December 31, 1990 (n = 2,593; 58,474 person-years; 98% follow-up). Significantly higher than expected mortality rates were found for all cause mortality (Standardized mortality ratio [SMR] = 110; 95% confidence interval [95% CI] = 1.04-1.17), all malignant neoplasms (SMR = 125; 95% CI = 1.10-1.41), cancer of the esophagus (SMR = 213; 95% CI = 1.01-3.91), cancer of the colon (SMR = 187; 95% CI = 1.29-2.59), cancer of the kidney (SMR = 2.08, 95% CI = 100-3.82), Hodgkin's disease (SMR = 313; 95% CI = 1.01-7.29), cirrhosis of the liver (SMR = 150; 95% CI = 1.00-2.16), and suicide (SMR = 153; 95% CI = 1.00-2.24). All accidents were significantly lower (SMR = 53; 95% CI = 0.34-0.79). Mortality by years of police service showed higher than expected rates for (1) all malignant neoplasms in the 1- to 9-years-of-service group; (2) all causes, bladder cancer, leukemia, and arteriosclerotic heart disease in the 10 to 19-year group; and (3) colon cancer and cirrhosis of the liver in the over 30 years of service group. Hypotheses for findings are discussed.

Cohort mortality study of prostate cancer among chemical workers.

A retrospective cohort mortality study was conducted at a chemical plant producing acetic acid and acetic anhydride, two chemicals essential in the synthesis of cellulose triacetate fiber. Previously, we reported excess mortality from biliary tract and prostate cancers among workers in cellulose triacetate fiber manufacturing plants. In the present investigation, an excess of prostate cancer (SMR = 330.4; 95% confidence interval = 121.3-719.1) was observed among former chemical plant workers, some of whom had been exposed to both acetic acid and acetic anhydride. These apparent increases in mortality are difficult to interpret biologically, particularly in light of recent suggestions concerning the role of endocrine factors. Additional work is planned to more fully characterize potential occupational exposures that might explain the etiology of prostate cancer.

Mortality of workers exposed to dieldrin and aldrin: a retrospective cohort study.

OBJECTIVE: To investigate the occurrence of long term health effects in humans exposed to aldrin and dieldrin, with an update of an earlier retrospective cohort mortality study. METHODS: A group...

Mortality in a group of tar distillery workers and roofers.

A retrospective cohort mortality study was conducted to assess long-term health risk in a group of tar distillery workers and roofers in order to investigate the existence of carcinogenic effects related to the occupational exposures. The study population consisted of 907 tar distillery workers and 866 roofers, employed at least one half-year between January 1947 and January 1980. This group was followed for mortality until January 1988. For the deceased workers the cause of death was provided by the Central Bureau of Statistics. The observed cause-specific mortality was compared with the expected cause-specific mortality calculated by means of the national mortality rates of The Netherlands. Mortality from cancer of the lungs and trachea was higher than expected in both groups, but not statistically significant. In addition the roofers had experienced an excess mortality rate from external causes. The study provides some additional support for the carcinogenicity of coal tar exposures, but the findings were not statistically significant.

An update of mortality from all causes among white uranium miners from the Colorado Plateau Study Group.

To place previously recognized mortality risks into the context of the total mortality from all causes, an updated retrospective cohort mortality study was conducted on 3,238 white males from the US Public Health Service cohort of Colorado Plateau uranium miners. Vital status was followed from 1960 through 1990. Life-table analyses used combined New Mexico, Arizona, Utah, and Colorado mortality rates for external comparison and mortality risks within the lowest radon-exposure or duration-employed category for internal comparison. Significantly elevated SMRs were found for pneumoconioses (SMR = 24.1, 95% CI 16.0-33.7), lung cancer (SMR = 5.8, 95% CI 5.2-6.4), tuberculosis (SMR = 3.7, 95% CI 1.9-6.2), chronic obstructive respiratory diseases (SMR = 2.8, 95% CI 2.2-3.5), emphysema (SMR = 2.5, 95% CI 1.9-3.2), benign and unspecified tumors (SMR = 2.4, 95% CI 1.0-4.6), and diseases of the blood and blood-forming organs (SMR = 2.4, 95% CI 1.0-5.0). No significantly lowered SMRs were found for any disease. For lung cancer and pneumoconioses standardized rate ratios increased with increasing exposure to radon progeny or duration of employment. Most findings from this update are consistent with previous studies. Not observed were previously elevated SMRs for chronic nephritis and for acute alcoholism. New findings observed were elevated SMRs for benign and unspecified tumors and for diseases of the blood and blood-forming organs. The most important long-term mortality risks for the white uranium-miners continue to be lung cancer and pneumoconioses, for which SMRs remain significantly elevated after a mean period of 22.4 years since last uranium mining.

Cohort mortality study of rubber and plastics product makers in Italy.

A retrospective cohort mortality study was carried out in 20 industrial factories in the Local Health Unit Bologna Sud (Emilia Romagna, Italy), where different rubber and plastics products were manufactured. The cohort consisted of 925 subjects (578 males and 347 females) employed for at least six months continuously; follow-up was between the beginning of operation of each factory, ranging between mid fifties and mid seventies, and 31 December 1989. For those exposed more than one year cause specific Standardized Mortality Ratios (SMRs) were computed using regional rates for comparison, 90% confidence intervals (CI) were calculated assuming the Poisson distribution. Among the 748 subjects employed for more than one year (457 males and 291 females) there were no lost to follow-up, 54 individuals were dead (41 males and 13 females) and for three subjects the cause of death was unknown. The results showed that all causes mortality was above expectancy in the total cohort (SMR = 123; 54 Obs; 90% CI = 97-154), among males (SMR = 117; 41 Obs; 90% CI = 89-152) and females (SMR = 143; 13 Obs; 90% CI = 85-228). Increased mortality for all malignant tumours was observed in the total cohort (SMR = 150; 25 Obs; 90% CI = 104-209) and for both genders. All nine lung cancer cases were observed among males, the SMR was equal to 218 and was statistically significant; seven cases occurred at duration of exposure less than 10 years and six at latency up to 20 years. The interpretation in terms of causality of the present investigation is limited by the small number of observations and by exposure definition solely in terms of employment in the study factories; nonetheless the results are indicating the existence, in this group of rubber and plastics product makers, of an adverse health effect which deserve further investigation.

Mortality among Navajo uranium miners.

To update mortality risks for Navajo uranium miners, a retrospective cohort mortality study was conducted of 757 Navajos from the cohort of Colorado Plateau uranium miners. Vital status was followed from 1960 to 1990. Standardized mortality ratios were estimated, with combined New Mexico and Arizona non-White mortality rates used for comparison. Cox regression models were used to evaluate exposure-response relationships. Elevated standardized mortality ratios were found for lung cancer (3.3), tuberculosis (2.6), and pneumoconioses and other respiratory diseases (2.6). Lowered ratios were found for heart disease (0.6), circulatory disease (0.4), and liver cirrhosis (0.5). The estimated relative risk for a 5-year duration of exposure vs none was 3.7 for lung cancer, 2.1 for pneumoconioses and other respiratory diseases, and 2.0 for tuberculosis. The relative risk for lung cancer was 6.9 for the midrange of cumulative exposure to radon progeny compared with the least exposed. Findings were consistent with those from previous studies. Twenty-three years after their last exposure to radon progeny, these light-smoking Navajo miners continue to face excess mortality risks from lung cancer and pneumoconioses and other respiratory diseases.

Cancer Mortality Patterns Among Women Who Served in the Military

In response to concerns of women veterans regarding the long-term health effects of military service in Vietnam, the Department of Veterans Affairs has been conducting a retrospective cohort mortality study of women Vietnam veterans. Military records were used to identify approximately 4600 women who served in Vietnam between July 4, 1965, and March 28, 1973, and a comparison cohort of nearly 5300 women who served during the same time frame but not in Southeast Asia or the Pacific theater. Current data include vital status determinations as of December 31, 1991, with a total of 532 deaths and an average follow-up of just over 20 years for both groups. Both the Vietnam and non-Vietnam women cohorts had a significant deficit of deaths from all causes compared to women in the US population. The two cohorts showed no difference in total mortality or in deaths from all cancers. A significant excess risk of pancreatic cancer was observed among Vietnam nurses compared to either non-Vietnam nurses (relative risk = 5.74) or women in the US population (standardized mortality ratio (SMR) = 2.78). Vietnam nurses also had an elevated risk of dying from cancer of the uterine corpus. Non-Vietnam nurses had a higher lung cancer mortality rate than women in the general population (SMR = 1.55) or nurses who served in Vietnam. Observed deficits of deaths from all causes and circulatory system diseases generally confirm a healthy selection bias for entry into and retention in the military that has been observed among men serving in the Armed Forces.

Women in the public sector: cancer mortality.

Very few mortality occupational studies of female workers have been published, even though the number of women in the workforce has increased dramatically to reach more than 45%. Public sector employees comprise 12% of the female workforce. This article reports the findings of a retrospective cohort mortality study of 1371 full-time female employees of the city of Buffalo, New York, who were employed between January 1, 1950, and October 1, 1979, and have worked a minimum of 5 years. The majority of women were hired in the 1940s and early 1950s and began employment after age 30. This predominantly white-collar, service-oriented female cohort demonstrated significantly lower all-cause mortality than that expected based on US mortality rates for white females. The highest observed numbers of cancer deaths were for breast, digestive, and respiratory cancers. The majority of person-years were accrued in clerical and service occupations. Higher-than-expected mortality was shown for reproductive and respiratory cancers among professional employees; digestive cancers, diseases of the nervous system, and pneumonia among clerical workers; and cancers of the lung and brain and diseases of the digestive system, especially ulcers, among service employees. Because these results are based on few observed cases, they must be interpreted cautiously.

Modeling epidemiologic studies of occupational cohorts for the quantitative assessment of carcinogenic hazards.

Epidemiologic studies of occupational cohorts have played a major role in the quantitative assessment of risks associated with several carcinogenic hazards and are likely to play an increasingly important role in this area. Relatively little attention has been given in either the epidemiologic or the risk assessment literature to the development of appropriate methods for modeling epidemiologic data for quantitative risk assessment (QRA). The purpose of this paper is to review currently available methods for modeling epidemiologic data for risk assessment. The focus of this paper is on methods for use with retrospective cohort mortality studies of occupational groups for estimating cancer risk, since these are the data most commonly used when epidemiologic information is used for QRA. Both empirical (e.g., Poisson regression and Cox proportionate hazards model) and biologic (e.g., two-stage models) models are considered. Analyses of a study of lung cancer among workers exposed to cadmium are used to illustrate these modeling methods. Based on this example it is demonstrated that the selection of a particular model may have a large influence on the resulting estimates of risk.

Cohort study among workers exposed to benzene in China: I. General methods and resources

Benzene is recognized internationally as a leukemogen, but the available data to clarify dose-response relationships and examine risks of malignancies other than leukemia are sparse. A collaborative study was therefore carried out to expand on a previous retrospective cohort mortality study of Chinese benzene-exposed workers. Methods and resources used in the 16-year follow-up of 74,828 benzene-exposed and 35,805 unexposed workers employed for any length of time during 1972-1987 in 712 factories in 12 cities in China are described. Details are provided of the study organization, assessment of benzene exposures since 1949, characterization of factories and workers by exposure status, city, and sex, identification and confirmation of cancers and other deaths, and quality control procedures. The distinguishing features of the study are discussed in relation to earlier cohort studies, and study limitations as well as strengths are presented.