Mycoplasma pneumoniae infection and its genotypical characterization in children of Hokkaido, Japan.

To investigate the etiology of Mycoplasma pneumoniae infections we conducted a prospective study covering the total pediatric population in Hokkaido, Japan. Paired sera for serologic assays were available for more than half of the cases (n = 921; 398 as pneumonia and 523 as bronchitis). The nasopharyngeal swabs were also collected for isolation and PCR study. The types of P1 gene from clinical isolates of M. pneumoniae obtained from two different areas of Hokkaido, Sapporo and Kushiro, were determined by PCR-RFLP assay. M. pneumoniae was identified in 174 (43.7%) out of 398 patients with pneumonia and was identified in 78 (14.9%) out of 523 (86.2%) patients with bronchitis. P1 genes of 14 clinical isolates of M. pneumoniae were classified into 13 group II and 1 group I. Two clinical isolates were unclassified by PCR-RFLP assay. Mycoplasma infections were seen even in patients less than 5 years of age. Generation of antigenic variation by DNA recombination may occur in clinical isolates.