Objectives: To determine the prevalence of atypical pneumonia and clinical presentations in patients with
community acquired pneumonia (CAP).
Material and Method: A prospective multi-centered study was performed in patients aged ≥ 2 years with the
diagnosis of CAP who were treated at seven governmental hospitals in Bangkok from December 2001 to
November 2002. The diagnosis of current infection was based on ≥ 4 fold rise in antibody sera or persistently
high antibody titers together with the presence of DNA of M.pneumoniae or C.pneumoniae in respiratory
secretion or antigen of L. pneumophila in the urine. Clinical presentations were compared between patients
with atypical pneumonia and unspecified pneumonia.
Results: Of 292 patients, 18.8% had current infection with atypical respiratory pathogens (M. pneumoniae
14.0%, C.pneumoniae 3.4%, L.pneumophila 0.4% and mixed infection 1.0%). Only age at presentation was
significantly associated with atypical pneumonia in adults, while absence of dyspnea, lobar consolidation,
and age ≥ 5 years were significant findings for atypical pneumonia in children.
Conclusion: The present study confirms the significance of atypical pathogens in adults and children. Moreover,
lobar consolidation is likely to predict atypical pneumonia in childhood CAP.

Keywords: Prevalence, Clinical, Atypical pathogens, Pneumonia