British Journal of Industrial Medicine, 1980; 37: 55-62 Microbial and immunological investigations and remedial action after an outbreak of humidifier fever

ABSTRACT Humidifier fever (Monday sickness) occurring in office staff in a factory processing rayon presented as pyrexia with a polyuria and leucocytosis on the first day back to work after a break during the winter half of the year. Chest radiographs showed no abnormalities but pulmonary function tests indicated mild airways obstruction in the affected group as a whole. Respirable dust samples taken on a Monday when 11 cases occurred were not pyrogenic, indicating that a mechanism other than direct pyrogen activity produced the pyrexia. Efforts were then directed to determining an immunological basis for the episodes. In particular, Thermoactinomyces vulgaris, previously held responsible for humidifier fever, was studied. During the episode of 11 cases, the number of viable airborne spores of this organism was far higher than on Mondays when no cases occurred. In a second episode of nine cases, however, the airborne viable count was of the same order as non-episode Mondays. Extracts ofT vulgaris produced lines of precipitation in gel diffusion studies with roughly half the office staff sera tested, but no correlation was observed between precipitin line formation and disease. A similar proportion of normal sera reacted against this extract. Extracts of dust lying on the topside surface of the suspended ceiling above the office, however, produced precipitin lines with sera fro