Comparison of soybean epidemic asthma and occupational asthma.

Asthma is an important public health problem because of its increasing prevalence and associated morbidity. It is a major research issue because its aetiology is not established and the reasons for its increasing occurrence are unknown. Occupational asthma is a valuable model of asthma caused by specific environmental exposures which could be useful for a better understanding of the disease.' Retrospective and prospective studies have shown that, for most of its causes, occupational asthma occurs during the first two years of exposure. Both the intensity and timing of exposure have been found to be risk factors for occupational asthma. Prospective investigations in laboratory animal workers have found a higher prevalence ofnew work-related symptoms in those exposed to higher airborne concentrations of antigen. Factors such as atopy and smoking have been reported to increase the risk of some causes of occupational asthma. Long term follow up of patients with occupational asthma has shown persisting symptoms, airways hyperresponsiveness, and evidence of sensitisation many years after avoidance of exposure to the initiating cause. A similar pattern of interrelationships has been observed in soybean epidemic asthma.2 In November 1979 soybean started to be unloaded in the harbour of Barcelona and, in 1981, the first asthma outbreak was described. Asthma outbreaks were repeatedly identified until 1987 when it was established that soybean unloaded at a particular silo was the causal agent. The unloading of soybean was stopped until appropriate filters had been installed in the responsible silo. This intervention prevented further outbreaks of asthma. Several studies have been conducted to assess the magnitude and characteristics of the epidemic as well as its aetiology. Current evidence suggests that soybean epidemic asthma is a useful model of community asthma which has many similarities to occupational asthma. In this review we have compared the characteristics of soybean epidemic asthma and occupational asthma, with special emphasis on the nature of the risk factors for both conditions.