Aetiology and risk factors of community-acquired pneumonia in hospitalized patients in Norway

Background and Aims: In Norway, data on the aetiology of community-acquired pneumonia (CAP) in hospitalized patients are limited. The aims of this study were to investigate the bacterial aetiology of CAP in hospitalized patients in Norway, risk factors for CAP and possible differences in risk factors between patients with Legionnaire's disease and pneumonia because of other causes. Methods: Adult patients with radiologically confirmed CAP admitted to hospital were eligible for the study. Routine aerobic and Legionella culture of sputum, blood culture, urinary antigen test for Legionella pneumophila and Streptococcus pneumoniae, polymerase chain reaction detection of Chlamydophila pneumoniae, Mycoplasma pneumoniae and Bordetella pertussis from throat specimens, and serology for L. pneumophila serogroup 1-6 were performed. A questionnaire, which included demographic and clinical data, risk factors and treatment, was completed. Results: We included 374 patients through a 20-month study period in 2007-2008. The aetiological agent was detected in 37% of cases. S. pneumoniae (20%) was the most prevalent agent, followed by Haemophilus influenzae (6%) and Legionella spp. (6%). Eight Legionella cases were diagnosed by urinary antigen test, of which four also had positive serology. In addition, 13 Legionella cases were diagnosed by serology. The degree of comorbidity was high. An increased risk of hospital-diagnosed Legionella pneumonia was found among patients with a diagnosis of chronic congestive heart failure. Conclusion: Our results indicate that S. pneumoniae is the most common bacterial cause of pneumonia in hospitalized patients, and the prevalence of Legionella pneumonia is probably higher in Norway than recognized previously.