Community-acquired pneumonia (CAP) is often misdiagnosed and improperly treated. Since it is not a reportable disease we do not have exact figures, but data from the USA suggest that there are approximately four million cases per year resulting in more than 600 000 hospitalisations, 64 million days of restricted activity and 45 000 deaths annually. The overall yearly cost associated with CAP is estimated at US$9–10 billion.

The lack of rapid, sensitive and specific methods to diagnose the aetiological pathogen in a particular patient with CAP means that the physician must often institute antimicrobial treatment without knowing with any degree of certainty what the pathogen is. Given the large number of potential aetiological agents—such as bacteria (Streptococcus pneumoniae, Haemophilus influenzae, Staphylococcus aureus), atypical organisms (Mycoplasma pneumoniae, Chlamydophila pneumoniae, Legionella species) and viruses—this represents a significant problem, particularly for patients ill enough to require admission to hospital.

A careful history and physical examination plus laboratory tests and procedures such as sputum Gram stain and culture, blood cultures and chest radiography have been shown to be unreliable in identifying the pathogen responsible for pneumonia in most patients with CAP.

Streptococcus pneumoniae, which is arguably the most important cause of CAP, can be particularly difficult to diagnose. Its identification in sputum may simply represent colonisation and its isolation from blood is woefully insensitive.1 The diagnosis of Legionnaire's disease in patients with CAP is dependent upon culture and serological testing, both of which have their problems.2 The development of urinary antigen tests for both pneumococcal and Legionella antigens has helped to expedite and improve the diagnostic process. The overall sensitivity …