A family outbreak of Chlamydia pneumoniae infection.

Chlamydia pneumoniae, a newly described Chlamydia species, has been shown to be a cause of acute respiratory tract infection in both adults and children, but its role in human infection is still under investigation. Here we present a family outbreak of C. pneumoniae infection where three members of a family presented with a 'flu-like illness' and acute upper respiratory tract infection which did not improve despite penicillin or septrin therapy. No history of exposure to birds, pets or animals was obtained. As C. pneumoniae isolation from respiratory secretions is not without difficulty, diagnosis usually relies currently on serum-based tests. In this study C. pneumoniae specific IgM determined by the micro-immunofluorescence test was detected in the three clinical cases. All three cases had an elevated complement-fixing antibody titre to Psittacosis-LGV antigen, which may have suggested psittacosis, if type-specific tests had not been performed. In addition, three other members of the family had C. pneumoniae-specific IgG antibody although specific IgM was absent. These three younger members of the family had been symptomatic in the month preceding symptoms in their older sibling and their parents. All the symptomatic members of the family made a complete recovery on tetracycline therapy.