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Authors of a systematic review are advocating a large collaborative and carefully standardised study to determine best advice for patients with occupational asthma, in the light of published findings on outcome. Better evidence is needed, they say.
Patients' prospects seem poor, by the two outcomes assessed—complete symptomatic recovery and physiological recovery after antigenic exposure has ceased. About a third of patients overall achieved complete recovery from symptoms, based on 39 original studies covering 1681 patients with a median follow up of 31 (range 6–240) months. Potential factors affecting this outcome were increased age and clinic based populations, with lower pooled prevalences for 100% recovery. Physiological recovery was also limited, as non‐specific bronchial hyper‐responsiveness (NSBHR) persisted after diagnosis in most of the 28 studies identified, covering 695 patients with a median follow up 37(6–240) months.
However, variation among studies was significant for both outcomes and the authors suspect length of follow up may be important. Most patients were from specialist clinics—an important source of bias. The few studies of workplace populations showed a higher pooled prevalence of recovery from symptoms than clinic based populations and lower pooled prevalence of NSBHR but at best were only borderline significant.
The analysis is compromised too by variation in study size and methods, possible overlap between some study populations, and differences in the way outcomes were measured. Added snags were inability to control for other important aspects like severity of asthma at diagnosis or use of protective measures.
Rachiotis G, et al. Thorax 2007;62:147–152.
Please visit the Occupational and Environmental Medicine website [www. occenvmed. com] for a link to the full text of this article.