[Atypical pathogens in adult patients admitted with community-acquired pneumonia].

Objective: To investigate the current status of atypical pathogen associated infections in community-acquired pneumonia (CAP) in adults, and their clinical attributes.
Methods: Clinical data, sputum specimens from acute phase, and paired sera from acute- and convalescent-phases of CAP in 153 adult patients were collected from May 2005 to May 2008 in multiple medical centers. Chlamydia pneumoniae (Cpn) IgG antibody, and Legionella pneumophila (LP) mixed IgG, IgA and IgM antibodies were determined by indirect immuno-fluorescent assay. Mycoplasma pneumoniae (Mpn) mixed IgG, IgA and IgM antibodies were determined by passive agglutination assay. All the sputum specimens were routinely cultured for bacterial isolation.
Results: Fifty-two (34%) out of the 153 cases were diagnosed as atypical CAP per the paired serum-antibody assay. Forty-seven of the 52 atypical CAP cases were infected by one atypical pathogen, 38 with Cpn, 4 with Mpn, and 5 with LP, while 5 out of the 52 atypical CAP cases were infected by 2 pathogens, Cpn and Mpnin 2, Cpn and LP in 3 cases. Eleven cases (21.2%) out of the 52 patients with atypical pneumonia were complicated with bacterial infection. Except peripheral white blood count was significant increased in the group of typical (bacterial only) pneumonia (WBC > 10 × 10⁹)/L, P = 0.03), all the other clinical parameters did not show statistically significant difference between the typical and the atypical pneumonia groups.
Conclusions: Our data suggest that Chlamydia pneumoniae, Mycoplasma pneumoniae and Legionella pneumophila are common pathogens of adult CAP. Chlamydia pneumoniae might be the most frequent atypical pathogen associated with atypical CAP.