Conventional microbial methods can yield an aetiological diagnosis in almost all of the patients admitted with community-acquired pneumonia. Sputum examination, if accurately performed, is still one of the most important diagnostic tools. Antigen detection, especially for pneumococcal antigen, is a valuable and rapid method for diagnosing pneumococcal pneumonia even during antibiotic treatment. Because of the high fatality rate in severe community-acquired pneumonia, invasive procedures may be indicated and are useful; they are preferably performed before antibiotic treatment is initiated. Bronchoalveolar lavage has the advantage of sampling secretions from a relatively large part of the lobe, and this fulfils the requirements for appropriate specimens for all microbiological procedures. Polymerase chain reaction is the most promising new diagnostic technique in pulmonary infections. It can detect DNA or RNA of a low number of microorganisms with high accuracy in different biological fluids. Larger studies are necessary to investigate the impact of this technique on the aetiology, treatment and outcome of community-acquired pneumonia. Although serology is useful for aetiological and epidemiological studies, in the majority of cases the results of serology are available only after completion of treatment, and therefore seldom influence the choice of specific antibiotic.
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