The incidence and etiology of community-acquired pneumonia in fever outpatients.

The purpose of this study was to analyze the incidence, etiology and clinical characteristics of community-acquired pneumonia (CAP) among outpatients with sore throat and/or cough, and thus to provide theoretical basis for timely and accurate diagnosis and treatment for CAP. We used chest X-rays for fever (a temperature greater than 37.5°C) patients, who were recruited since 2007, presenting with sore throat and/or cough. The patients' age, gender, days of fever, respiratory symptoms (e.g. cough and sputum), peripheral blood count and etiology (pathogens) of CAP were recorded. Of all the 6539 fever outpatients, those aged 10-39 and above 60 years old accounted for 61.0% and 15.6%, respectively. In total, 402 were diagnosed with CAP with an incidence rate of 6.1%. Among them, 38.1% were above 60 years old. The prevalence increased with age. Of the 402 CAP patients, 36.8% (148/402) presented no respiratory symptoms and 30.1% (121/402) had positive etiology. The top three pathogens were Mycoplasma pneumoniae (23.1%), Streptococcus pneumoniae (17.3%) and Haemophilus influenzae (9.1%). Among the 121 etiology-positive patients, 14 cases were mixed infections (at least one atypical pathogen). Nine cases were M. pneumoniae mixed with bacterial/virus infection, and five cases were Chlamydia pneumoniae mixed with other bacteria/mycoplasma infection. We found that fever outpatients have a higher prevalence of CAP, which increases with age, i.e. older people are more susceptible to CAP. S. pneumoniae and H. influenzae are common pathogens in CAP; however, atypical pathogens, especially M. pneumoniae, remain the most common pathogens in CAP.