To assess factors related to the severity of atypical pneumonia caused by M. pneumoniae, C. pneumoniae and L. pneumophila in children, Nasopharyngeal swabs or aspirates and paired sera of total 722 patients (ranging 1 to15 years of age) treated in Respiratory Department of National Hospital of Pediatrics in Vietnam during 7/2010 - 3/2012, were collected. Multiplex PCR and enzyme-linked immunosorbent assay were used to detect M. pneumoniae, C. pneumoniae and L. pneumophila in those specimens. Status of co-infection with virus and/ or typical respiratory bacteria were evaluated and graded. Results: percentage of community acquired pneumonia due to M. pneumoniae, C. pneumoniae, and L. pneumophila in hospitalized children have age of 1-15 years was 29.8 percent. Mycoplasma pneumoniae positive in 190 (26.3 percent) cases, C. pneumoniae in 27 cases (3.7 percent), L. pneumophila in 13 cases (1.8 percent). In general, co-infection in 76 cases (33 percent). Among them, co-infection of atypical etiology in 15 cases (7 percent)
co-infection with typical bacteria in 38 cases (17,7 percent)
co-infection with respiratory viruses in 19 cases (8.8 percent). Patients positive for atypical bacteria co-infected with virus and/ or typical bacteria were significantly more likely to have severe pneumoniae than patients infected with only atypical bacteria (44.33 percent vs 15.25 percent
OR= 4.42
p0.001), which were (27.8 percent vs 9.3 percent
OR