Protective value of dust respirators in extrinsic allergic alveolitis: clinical assessment using inhalation provocation tests.

Six subjects with budgerigar fancier's lung, pigeon breeder's lung, or mushroom worker's lung underwent identical paired inhalation provocation tests of 20 minutes to five hours duration (mean 2.3 hours) using a natural method of antigen exposure. For one test of each pair, the subjects were protected by the use of industrial dust respirators that incorporate electrostatically charged, resin-impregnated merino wool filters. The unprotected challenges provoked late responses of mild to moderate severity, that were characteristic of extrinsic allergic alveolitis. These were monitored by methods described previously, using four subjective and six objective monitoring tests. A score of 1 was allowed for each monitoring test showing a significant change. A combined monitoring score of 32/57 was associated with the unprotected challenges-that is, 56% of the maximum score possible. The respirators successfully protected four of the subjects from any suspicion of a positive response. The remaining two subjects reported symptoms of minimal severity, but there was no independent confirmatory evidence of positive reactions. The combined monitoring score associated with all six protected challenges was 2/60 (3%), while that associated with corresponding control challenges was 3/73 (4%). We conclude that respirators of this type can offer substantial, and in most cases complete, protection against single exposures to environmental dusts that may provoke extrinsic allergic alveolitis.