Age Specific Prevalence of Antibodies against Chlamydia pneumoniae in Iceland

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Abstract
Chlamydia pneumoniae is a newly recognized common cause of respiratory tract infections. The aim of this study was to examine its prevalence in Iceland. The study was based on 1020 serum samples from individuals 0–99 years old. The samples were divided into 10–year age groups. IgG and IgM antibodies were determined with microimmunofluorescence assay. An IgG titer p < 0.001), but rose linearly to age 70 (p < 0.005). 34 samples were IgM positive on initial testing; most from the older age groups. 12 were rheumatoid factor positive as well. After treatment with caprine antihuman IgG antibodies all became negative. The prevalence of C. pneumoniae infections is high in Iceland according to these results and similar to that in neighbouring countries. The presence of IgM rheumatoid factor may cause false positive tests for pathogen-specific IgM by immune complex binding with pathogen-specific IgG, thereby requiring its removal before testing.