Outbreak of Chlamydia pneumoniae infection in a Japanese nursing home, 1999-2000.

Objective: To identify risk factors for infection and severe illness due to Chlamydia pneumoniae.

Methods: To identify risk factors for infection, we conducted a case-control study among nursing home residents who had onset of symptoms during December 1, 1999, to February 20, 2000. To identify risk factors for severe illness among nursing home residents, we conducted a retrospective cohort study.