Repeaters count: a sentinel method for asthma outbreaks. Barcelona Soybean-Asthma Group.

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Abstract
BACKGROUND--Asthma outbreaks have not been detected in Barcelona, Spain since the epidemic of 1981-7. On 29 October 1994 several subjects attended a Barcelona hospital because of acute attacks of asthma and were identified as former soybean epidemic asthma patients (repeaters), raising the possibility of an asthma soybean-related episode. The usefulness of counting repeaters to evaluate small increases of acute asthma in a non-epidemic period is illustrated. METHODS--A retrospective identification of asthma admissions was performed, pollution filters collected before and after the index day were analysed for contents of low molecular weight soybean allergen, and soybean unloading activities were investigated. RESULTS--There was no epidemic increase of asthma patients during this day in the whole of Barcelona, but an unusually high number were repeaters (seven observed v 0.483 expected). A relationship with increased levels of low molecular weight soybean allergen (U/m3) was detected in the available pollution filters collected the day before and after the index day. Two ships were unloading soybean in the city harbour on the index day. CONCLUSION--Soybean unloading at the harbour of Barcelona released soybean dust and produced a small cluster of emergency room visits for asthma in patients formerly affected by soybean asthma epidemics. It is suggested that counting repeaters could provide the basis for a systematic epidemiological surveillance of sensitised populations.