The influence of age and gender on the population-based incidence of community-acquired pneumonia caused by different microbial pathogens.

OBJECTIVES To determine the population-based incidence of community-acquired pneumonia (CAP) in adults and to assess the relative importance of age and gender on the incidence of infections caused by different microbial pathogens. METHODS A two-year prospective study in a well-defined geographic area of the Spanish Mediterranean coast. RESULTS The overall incidence rate of CAP was 12 cases (95% CI 11.25-13.45) per 10,000 person-years. Incidence rates increased by age (p<0.0001) and they were higher in males (16 versus 9 cases per 10,000 person-years; p<0.0001). The rate was especially high among males aged > or = 75 years (87 cases per 10,000 person-years). The incidence of pneumococcal pneumonia increased significantly with ageing and it was particularly high among people aged > or = 75 years (10 cases per 10,000 person-years). Very elderly people had also a 15-fold higher incidence of CAP associated with influenza virus and a 5-fold higher incidence of infections by Chlamydophila spp., than young adults. The incidence of infections with Legionella pneumophila also increased with age and it was 10 times higher in males. In contrast, the incidence of pneumonia caused by Mycoplasma pneumoniae was unrelated to age and gender. CONCLUSIONS Age and gender have a strong influence on the overall incidence of CAP and on the incidence of pneumonia caused by the main microbial pathogens, including not only Streptococcus pneumoniae, but also influenza virus, Chlamydophila spp. and L. pneumophila. Ageing is associated with a higher risk of acquiring pneumonia by S. pneumoniae, influenza virus and Chlamydophila spp., whereas male gender increases greatly the incidence of L. pneumophila and Chlamydophila spp.