Preliminary report of mortality among workers compensated for work-relatedasthma

Background Although fatalities due to asthma have been reported among subje cts with occupational asthma (OA) associated with re-exposure, groups of su bjects with work-related asthma have not been systematically followed up fo r mortality. During a review of compensation claims for asthma in Ontario, we identified 3 respiratory deaths among subjects previously compensated fo r OA for whom their surviving spouses received death benefits. This suspect ed "cluster" prompted us to undertake an investigation to examine mortality pattern among workers compensated for work-related asthma. Methods Subjects receiving compensation for OA or aggravation of asthma (AA ) between 1980 and 1993, and a comparison sample of workers with claims for musculoskeletal injuries during the same period were identified from the O ntario Workers' Compensation Board. We also identified another comparison g roup of non-compensated asthmatic patients seen at a hospital clinic during the same period. The files of those with work-related asthma were reviewed to determine if OA or AA was adequately documented. Mortality was ascertai ned by linkage with the Mortality Database at the Ontario Cancer Registry t hrough 1996. We compared the mortality of the three groups with that expect ed in the general population of Ontario using SMRs, and directly by proport ional-hazards regression. Results The study included 3,070 subjects: 1,112 with work-related OA/AA wi th adequate documentation, 1,556 with work-related injuries, and 402 patien ts with non-work-related asthma. Of the 66 deaths identified only 2 deaths were due to asthma, both in the work-related asthma group: one from the ind ex cluster; and one not previously identified A second index death was code d as dying from COPD not elsewhere classified (ICD9 496), while the third i ndex death also died of asthma but there was not sufficient information doc umenting OA to include the subject in the analyses. As compared with the ge neral population, there were fewer deaths than expected from most causes, e xcept for deaths among the work-related asthma claimants and the nonwork-re lated asthma patients from respiratory diseases (SMRs 1.3 and 5.9 respectiv ely; 0.5 among injury claimants), all chronic obstructive lung disease (ICD 9 490-496; SMRs 2.3 and 77 respectively), and asthma (SMRs 18.2 and 0 respe ctively). In direct comparison of the work-related asthma claimants with th e injury claimants, the risk of death appeared elevated from respiratory di sease (RR 2.6) and ischemic heart disease (IHD) (RR 2.8) but the confidence intervals included unity. Conclusions This preliminary report raises the possibility that serious out comes, including excess deaths from: respiratory disease, in particular ast hma, may occur among those with work-related asthma even in the absence of re-exposure. However, the findings are inconclusive given that the number o f deaths was small and we identified only one new asthma death in addition to the index cluster We also observed for the first time that deaths due to circulatory disease, particularly IHD, may also be increased among such wo rkers; this needs to be confirmed elsewhere. Am. J. Ind. Med. 35:465-471, 1 999. (C) 1999 Wiley-Liss, Inc.