Investigating a single case of Legionnaires' disease: guidance for consultants in communicable disease control.

When a single case of legionnaires' disease is reported, it should be investigated to check whether or not it is linked to other cases or part of an outbreak. The investigation includes confirmation of the diagnosis, tracing the patient's movements during the incubation period, and reporting the case to the National Surveillance Scheme for Legionnaires' Disease at the PHLS Communicable Disease Surveillance Centre. If no common factors are identified between the cases and other cases reported previously, no further action is usually required, unless it is suspected that the infection was acquired in hospital. In these circumstances, the individual case and the hospital's water maintenance programme should be reviewed, and a search made for associated cases, because hospital patients are particularly susceptible to infection. Further steps may be necessary if the link with the hospital is confirmed.