Outbreak of Chlamydia pneumoniae infection in four farm families.

The epidemiology of Chlamydia pneumoniae infection was studied in an outbreak in four farm families living close together in Denmark. Eleven of 20 members of the families studied had bronchitis or pneumonia characteristic of Chlamydia pneumoniae infection. Serologic evidence of Chlamydia pneumoniae as causative agent was strengthened by a high incidence of epidemic infection. Transmission within families and a high frequency of disease versus asymptomatic infection are two findings which deviate from epidemiological patterns of Chlamydia pneumoniae infection as currently known.