Abstract: Objective To investigate the clinical features of community acquired pneumonia(CAP) due to Legionella pneumophila(Lp) and non-pneumophila Legionella species(non-Lp).Methods Sputum samples from patients with clinically diagnosed legionella pneumonia according to manifestations and serum antibody results were detected for legionella DNA with a duplex polymerase chain reaction(DPCR)method.Patients with the coincident positive results of sputum DPCR and serum antibody were divided into Lp pneumonia group(42 cases) and non-Lp pneumonia group(18 cases).The clinical data of patients from these two groups were analyzed and compared.Results The diagnosis of pneumonia due to Lp or non-Lp was further confirmed since the results of DPCR were in accordance with that of serum antibody in the patients.Lp pneumonia often occurred in summer-autumn season and was more often found in middle-aged person in good health;whereas the majority of non-Lp pneumonia happened to the old with underlying diseases and seemed to have no seasonal preference no season.When compared with non-Lp pneumonia,the patients with Lp pneumonia showed wider pulmonary involvement,higher incidence of pleural effusion and ARDS,as well as a more significant symptom of systemic toxicity and extra-pulmonary involvement(P<0.05).Conclusion The clinical characteristics of CAP due to Lp are different from those due to non-Lp.Early treatment with macroazalides and fluoroquinolone is the most important way to improve the prognosis.

Key words: community acquired pneumonia, Legionella pneumophila, non-pneumophila Legionella species, duplex polymerase chain reaction