Occupational asthma in cleaners: a challenging black box

An abiding feature of current occupational epidemiology has been the observation— in Europe and North America—of high rates of asthma-like symptoms in profes-sional cleaners.1 In comparison with ‘refer-ent ’ occupational groups such as office workers, risk estimates of around 1.5 have repeatedly been reported.2 Since there are very large numbers of people who work as cleaners one might expect these to be reflected in the experience of clinicians who see patients with asthma and in par-ticular those with a special interest in work-related disease. This does not, however, appear to be the case. In the past