Case-control study of serum immunoglobulin-E antibodies reactive with soybean in epidemic asthma

Since 1981, twenty-six asthma outbreaks have been identified in Barcelona, all coinciding with the unloading of soybean in the harbour. Serum from patients with epidemic asthma and individually matched controls with non-epidemic asthma was assayed for immunoglobulin-E (IgE) antibodies against soybean antigens by means of a radioallergosorbent test. In 64 of 86 cases (74.4%) there was a reaction with commercial soybean antigen extracts, compared with only 4 of the 86 controls (4.6%) (odds ratio = 61; lower 95% confidence limit = 8.1). The statistical significance was greater for reactions with extracts of soybean dust taken from Barcelona harbour (odds ratio, unquantifiably high; lower 95% confidence limit = 11.7). No other serological covariate (total serum IgE levels or specific IgE levels against the commonest airborne allergens or legumes) confounded the association between serum anti-soybean IgE antibodies and epidemic asthma. These results support a causal relation between the release of dust during unloading of soybean at the harbour and the occurrence of asthma outbreaks, suggesting an underlying allergic mechanism.