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Extrinsic allergic alveolitis caused by a cold water humidifier.

SIR-We read with interest the report by Dr AS Robertson and others (January 1987;42:32-7) of extrinsic allergic alveolitis caused by a cold water humidifier. The causative agent among the humidifier sludge responsible for the extrinsic allergic alveolitis remained elusive. There is a possibility that the alveolitis was due to bird fancier's lung caused by inhalation of avian droppings. This was not specifically sought by bronchial provocation testing despite the authors' findings of precipitating antibodies to budgerigar and pigeon droppings in all three subjects. Although there was no known contact with birds in any of these subjects, we have recently observed a reactivation of bird fancier's lung in a previous fancier who initially appeared to have had no avian contact for several years. Detailed investigations showed that she had been exposed to pigeon droppings through a skylight in the roof of the building in which she worked. Therefore can the authors reassure us that there was absolutely no likelihood of contamination of the humidifier with avian protein? In addition, we feel that it would have been informative to perform bronchial challenge testing with avian protein since a positive response in the presence of precipitins would be highly suggestive that this was the offending antigen in the sludge. AJ WILLIAMS