Cost effectiveness of surveillance for isocyanate asthma : finding an occupational health policy framework

Wild et al present an original cost effectiveness analysis for medical surveillance for isocyanate asthma in this issue of OEM.1 The general case for surveillance for isocyanate asthma is a compelling one. Most occupational physicians, practitioners, and researchers might rightly expect that if a cost effectiveness (CE) case cannot be made for this agent, it would be hard to make a case for most others. The causal link between isocyanate exposure and asthma is well established, and more is known about the pathophysiology, natural history, long term consequences, and benefits of medical surveillance in this instance than for most other occupational exposures.A mathematical simulation model was developed based on a carefully specified set of clinical parameters, drawing from empirical studies where possible (for example, in estimating sensitisation rates ranging from 0.7% to 5.3% per year), and well qualified expert opinion otherwise (for example, in estimating the chance of removal from exposure if a patient is diagnosed versus undiagnosed). Their “state transition” model compared passive case finding to surveillance (the heart of the CE analysis question as proposed) for a theoretical population of 100 000 otherwise healthy and exposed workers, predicting their progression over 10 years across three mutually exclusive “states”: healthy and exposed; symptomatic; and disabled. This alone is an impressive and valuable piece of research, integrating a substantial body of empirical research to show that surveillance is estimated to result in 700 fewer cases of disability over 10 years compared to passive case finding. While such a modelling exercise necessarily requires numerous assumptions and simplifications, each was well articulated and defensible.