How is the epidemiology of hypersensitivity pneumonitis?

Varies widely, 8.5% (half of them only have clinical manifestation) in agricultural areas Pigeon breeders 40-50% (and disease manifestation occurs in 6-21%) Outbreak from microbial contamination is 15% attacks and 70% exposed. Host factors are important (less frequent in non-smokers, atopic pt are not at increased risk, viral infections may play a role