A Technique to Re-Assess Epidemiologic Evidence in Light of the Healthy Worker Effect: The Case of Firefighting and Heart Disease

Abstract

The healthy worker effect (HWE) is a bias that is believed to have strongly affected the validity of previous cohort mortality studies on the relationship between firefighting and heart disease. There is a strong healthy hired effect (a component of the HWE) among firefighters, owing particularly to the recruitment of nondiabetic candidates. This is shown in previous studies in which the reported standardized mortality ratios for diabetes are much less than unity, generally around 0.3 to 0.5. Because diabetes is known to increase the risk of heart disease, a deficit of diabetes among firefighters is expected to lead to a deficit of heart injury and disease. This would make the cohort mortality studies incapable of detecting any increase in risk of heart injury and disease among firefighters. There is also a strong healthy worker survivor effect (another component of the HWE) among firefighters. In addition, heart disease is a classic example of the HWE because heart disease is chronic and its risk factors can be identified in the selection process. It is believed that (1) a major problem of previous studies on firefighting and heart disease is their failure to recognize the importance of the HWE when interpreting their results, and (2) a technique to re-assess results in light of the HWE is urgently needed. This article addresses the generally accepted principles relating to the HWE, including its definition and sources, and proposes a technique for re-assessing the literature in light of the HWE. The technique was applied to carefully re-assess 23 studies that provided direct evidence for the relationship between firefighting and heart disease. Before the re-assessment, 7 of the 23 studies showed positive evidence and 16 showed no evidence. After the re-assessment, 11 studies showed positive evidence and 12 showed no evidence. Based on the results of the re-assessment of the 23 studies, we concluded that (1) there is strong evidence of an increased risk of death overall from heart disease among firefighters; (2) there is insufficient evidence, even after considering the HWE, that there is an increased risk of death from aortic aneurysm among firefighters; and (3) there is insufficient evidence, even after considering the HWE, for a relationship between firefighting and any heart disease subtype, such as acute myocardial infarction.

Physiological Determinants of the Candidate Physical Ability Test in Firefighters

“…Choi reassessed 23 cardiovascular mortality studies in firefighters by taking the healthy worker effect in to consideration (14). Prior to re-assessment, 7 of 23 studies showed a link between firefighting and cardiovascular disease.…”

Developing regional workplace health and hazard surveillance in the Americas

“…After a period of collaboration and pilot projects, more sophisticated systems could be developed. For example, at a more complex level, there is a need to develop multinational common reporting standards (3), minimum datasets, strategies to reduce and prevent bias (13)(14)(15), including the healthy worker effect (16,17), code of practice on recording and notification of occupational sentinel health events (12), standard notification forms and questionnaires with standard questions (11), standard coding schemes (11), common data dictionaries, standard data analysis protocols, minimum statistical indicators (18,19), automated data analysis systems with built-in capability to provide early warnings (3,5), and standard reports with standard tables and diagrams (11).…”

Work-related Cerebrovascular and Cardiovascular Diseases (WR-CVDs) in Korea

“…Physicochemical risk factors encountered in the work environment that may induce or aggravate acute cardiovascular abnormalities such as arrhythmia, angina, myocardial infarction, and sudden death include carbon monoxide [3][4][5] , methylene chloride 6) , nitrates such as nitroglycerin 7) , solvents [8][9][10][11] , pesticides 12) , fluorocarbons and hydrocarbons 13) , and cold and heat 14) . Table 1 describes several typical cases of occupational cardiovascular disease in Korea due to physicochemical factors, according to the Occupational Health Safety Research Institute (OSHRI), KOSHA.…”