Chlamydia pneumoniae infections in Norway 1981-87 earlier diagnosed as ornithosis

Ornithosis has been a notifiable disease in Norway since 1957. During an outbreak of respiratory disease in 1981-82, described as ornithosis, contact with birds was stated in only 50% of the cases, suggesting that the infection was spread by interhuman transmission. A similar outbreak occurred in the western part of Norway in 1987. Serum specimens from altogether 260 patients, collected during the outbreaks in 1981-82 and in 1987, were investigated for antibodies against Chlamydia pneumoniae (strain TWAR). Evidence of recent infection with C. pneumoniae was found in 67.7% of the cases. The results indicate that the increased incidence of ornithosis in 1981-82 and in 1987 was due mainly to C. pneumoniae infections.