A survival analysis of vibration-related occupational disease and implications for evaluating interventions

Background Regular exposure to hand-arm vibration can lead to hand-arm vibration (HAVS) and carpal tunnel (CTS) syndromes. EU Directive 2002/44/EC, which aims to improve surveillance and reduce exposure to vibration at work, defines exposure limits for hand-arm-vibration. The aim is to investigate whether the staged implementation of the directive since 2005 has been associated with a change in the incidence of HAVS or CTS in European countries. To model the range of potential outcomes of the intervention, we sought to define an exposure-risk relationship based on the best available prospective longitudinal data for exposed workers. Methods In a series of studies, which have been subject of previous publications,1,2 forestry and stone workers were monitored at intervals of 1 to 5 years, on 1 to 4 occasions. Health status, annual hours of exposure and magnitude of vibration were recorded. In the present study, a novel analytical approach was applied to define a parametric survival function describing the incidence of HAVS as a function of various exposure metrics. Results Incidence of the vascular condition vibration-induced white finger was well described by a Weibull distribution with an increasing hazard rate. The resulting parametric equation reveals the role of duration of exposure and the vibration magnitude (m s-2) relative to a threshold magnitude. Conclusion The exposure-risk relationship, which differs in some respects from the exposure relationship described in current standards (e.g. ISO 5349-1, 2001), has a simple, mechanistically based form that can be easily applied to simulate the consequences of workplace interventions.