Effect of age on antibody titer to Mycoplasma pneumoniae.

Between January 1996 and September 1999, 13,650 serum samples from 12,337 patients were examined for antibodies to Mycoplasma pneumoniae at the Institute of Hygiene, University Hospital Vienna in the course of routine diagnosis. Antibody determination was performed by means of the microparticle agglutination assay Serodia Myco II. Overall, positive results (antibody titer > or = 1:40) were obtained in 2028 patients (16.4%). Age details were available for analysis in 2016 positive patients. Young children (< or = 9 y) who tested positive showed a geometric mean titer of 1:137.9 (95% confidence interval: 117.7-161.4). The geometric mean titers of positive patients decreased significantly with age (Spearman's correlation coefficient -0.20; p < 0.0001). Only 1/87 patients with serological evidence of M. pneumoniae infection aged > or = 70 y showed a titer of > or = 1:320. These data highlight the fact that, in the elderly, acute M. pneumoniae infection has to be considered in cases with slightly elevated antibody titers, which are usually referred to as borderline in children and young adults.