Occupational hypersensitivity pneumonitis in Japan: data on a nationwide epidemiological study

Diagnostic criteria were prepared for hypersensitivity pneumonitis (HP) and a nationwide survey was conducted to investigate epidemiological and clinical characteristics of HP in Japan. The results are presented with special focus on occupational HP and on the key to the diagnosis of HP.

A questionnaire was completed by 185 doctors from 185 hospitals (response rate 89.5%). All cases were verified according to diagnostic criteria; 835 cases were classified as HP (653 definite and 182 probable). These 835 cases (total HP) and 99 possible cases of HP diagnosed during the 1980s were analysed and presented as a case series study.

Occupational HP was noted in 115 cases (13.8%). 21 occupations, and 20 aetiological antigens were listed. Farmer's lung: 68 cases (59% of occupational HP) was the most prevalent diagnosis followed by 19 industrial workers who handled chemicals (for example, isocyanate) and 10 office workers. Unique cases of mushroom, greenhouse, and silkworm farmers, and a new type of bagassosis are also described. Adverse environmental conditions, immunological findings on examination, antigen challenge, and pathological findings were all significantly lower for possible than for total HP. This was not true for clinical findings. The differences in antibody analysis (6% positive of possible HP v 59% of total HP) and environmental challenge (3% v 74%) were notable.

These data suggest that a careful interview about the environment and an antigen panel matched to variations in exposure are the key to the diagnosis.