Community-acquired pneumonia: definition, epidemiology, and outcome

Community-acquired pneumonia does not describe pneumonia acquired in the community. It represents a concept about a distinct clinical syndrome in distinct community patients. However, considerable differences still persist in European as well as in American literature with regard to its exact contents, including the assessment of immunosuppression, aspiration, tuberculosis, postobstructive pneumonia, and acquisition during stays in nursing homes. The definition of pneumonia is also not standardized, and this may impose the greatest difficulties in mild courses. The incidence of pneumonia probably does not differ between Europe and North America. The basic microbial patterns comprise (1) Streptococcus pneumoniae, (2) an atypical group, (3) non-pneumococcal-non-atypical group, and (4) the microbiologically negative group. The relative frequency of each group is affected by the severity of pneumonia, age, comorbidity, season, and individual risk factors. Prognostic factors associated with death should be arranged according to a clinically meaningful concept, including the differentiation of basic, baseline, and evolutionary factors. This concept allows the assessment of prognostic factors that reflect the premorbid condition of the patient, including the history of pneumonia up to the time of hospital admission, the severity of illness at initial evaluation, and the clinical evolution since the initiation of antimicrobial treatment.