Investigating and analysing workplace clusters of diseases: a Health & Safety Executive perspective

BACKGROUND: Clusters of disease arising in workplaces cause concern among the management of the company, the workers affected and their families and friends. Chance is the most likely explanation for their occurrence, although a number of real workplace hazards have been identified through their observation and investigation. Employers have a duty to investigate such occurrences in order to assess whether some unknown or unidentified hazard is at work and to take the appropriate action. Several papers have been published over the last 15 years or so that set out a method for investigating workplace clusters of disease. Aims This paper presents the steps in the approach taken by the Health & Safety Executive in Great Britain. METHOD: An initial step identifies the relevant stakeholders at the outset, in order to maintain a realistic expectation of what the investigation can hope to achieve and to open a dialogue. The main steps in the assessment are: (1) identifying cases; (2) determining the other parameters of the investigation; (3) statistically assessing the cluster; (4) examining potential exposures and assessing their biological plausibility; and (5) determining the overall significance of the cluster. The approach is illustrated throughout by examples.