Transmission of Chlamydia pneumoniae in young children in a Japanese family.

Chlamydia pneumoniae strain TWAR was isolated from the respiratory tract of a 5-year-old girl suffering from pneumonia. The IgM and IgG antibody titers to TWAR were 1:32 and 1:128, respectively. Cultures and serology for other common bacterial and viral respiratory pathogens were negative. Although she was treated with 35 mg/kg/day rokitamycin, TWAR was repeatedly isolated after treatment. Her 3-year-old sister developed acute bronchitis, and TWAR was isolated from her nasopharynx. She was treated with 43 mg/kg/day erythromycin with prompt improvement, and TWAR was not isolated after treatment. Although her mother, grandmother, and 8-month-old sister suffered from respiratory illness during these periods, TWAR was not isolated from them. The repeated isolations from the index patient suggest that infection was transmitted from sister to sister. This case represents the first reported isolation of TWAR from young children in the same household and the first from Japan.