Atypical bacterial pathogen infection in children with acute bronchiolitis in northeast Thailand.

BACKGROUND: Atypical bacterial pathogens--including Mycoplasma pneumoniae, Chlamydophila pneumoniae, and Chlamydia trachomatis--are important infectious agents of the respiratory system. Most current information pertains to adults and little is known about the role of these organisms in lower respiratory tract infections among young children with acute bronchiolitis.

METHODS: This study detected these pathogens in the nasopharyngeal secretions of children between 1 month and 2 years of age admitted with acute bronchiolitis to hospitals in Khon Kaen, northeast Thailand. The M pneumoniae and C pneumoniae in the nasopharyngeal secretions were detected using multiplex and nested-polymerase chain reaction (PCR), whereas PCR and restriction fragment length polymorphism were used to investigate C trachomatis. These samples were also tested by multiplex reverse transcriptase PCR for respiratory viruses, including respiratory syncytial virus (RSV), influenza A, influenza B, and human metapneumovirus.

RESULTS: Of the 170 samples taken from hospitalized children with acute bronchiolitis, 12.9% were infected with atypical bacteria and 85.3% with respiratory viruses. RSV was the most common causative viral agents found in 64.7% of the samples. M pneumoniae was the most common atypical bacterial pathogen (14/170, 8.2%) and most of the patients infected with it were between 6 and less than 12 months of age (71 cases). Of the infected cases in this age group, 7 of 14 were infected with M pneumoniae and 4 of 4 with C pneumoniae. Both M pneumoniae (13/14) and C pneumoniae (4/4) had etiologies indicating viral coinfections. Four (2.4%) of all of the cases had C trachomatis infections and all of these were infected with RSV, including three patients less than 6 months of age.

CONCLUSION: These results suggest that in children with virus-induced acute bronchiolitis coinfection with M pneumoniae, C pneumoniae, or C trachomatis can be expressed differently in each age group. These atypical bacteria may be the important infectious agents that induce severe illness of acute bronchiolitis.