Etiological agents of lower respiratory tract infections in Japanese children.

To investigate the etiology of pediatric community-acquired pneumonia and bronchitis, we conducted a prospective, population-based study covering the total population < 15 years of age in 16 municipalities in Hokkaido, Japan, during the period of April 2000 to March 2001. Chest radiographs were available for all cases (n = 921; 398 as pneumonia and 523 as bronchitis) and paired sera for serologic assays were available for more than half of the cases. The following specimens were also collected: nasopharyngeal swabs for viral, bacteriological, mycoplasmal and chlamydial studies, blood for serology and blood culture. The children were then followed-up on days 3, 7 and 14. Specific infecting organisms were identified in a total of 853 (92.6%) out of 921 patients (398 cases of pneumonia and 523 cases of bronchitis) including 205 with mixed infection as follows: Mycoplasma pneumoniae, 252 (274%) patients; respiratory syncytial (RS) virus, 188 (20.4%); influenza A virus, 110 (11.9%); Streptococcus pneumoniae, 95 (10.3%); Haemophilus influenzae, 90 (9.8%); Haemophilus parainfluenzae, 35 (3.8%); Staphylococcus aureus, 29 (3.1%); adenovirus, 27 (2.9%); Moraxella catarrhalis, 12 (1.3%); Pseudomonas aeruginosa , 7 (0.8%); Chlamydia pneumoniae, 6 (0.7%); and other agents, 2 (0.2%). Mycoplasma infections were seen even in patients less than 5 years and RS and influenza A virus infections in patients more than 5 years of age. The importance of M. pneumoniae and RS virus in the etiology of lower respiratory infections in Japanese children was confirmed.

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.