They can be grown in the laboratory on special culture media but will not be grown on routine examination of samples. Diagnosis is clinical, radiological and by serological blood tests. Mycoplasma years , where many cases are seen, occur every three to four years, alternating with periods when few, if any, such infections occur. Legionella pneumophila A Gram-doubtful rod which can be grown only on specialised culture media and will be missed on routine laboratory examination. The organism occurs in standing water ubiquitously and causes infection only when water vapour with a heavy bacterial load is inhaled.
Minor infection is common and largely unrecognised.
Diagnosis is clinical, radiological and serological or by antigen detection. Cases may be sporadic or occur in outbreaks often related to hotels or, depressingly, hospitals. Erythromycin alone or with rifampicin may be effective. Probably commoner than is thought because it is rarely considered or sought. It is a rare cause of mild to moderate respiratory-tract infection.