Legionnaires Disease

Infecting agent
Legionella pneumophila is known to cause pneumonia in humans and is responsible for both sporadic and clusters of cases.

Distribution
It is a ubiquitous organism with a worldwide distribution found in mud, environmental and recreational waters, cooling towers, air conditioning units, and many piped water supplies.

The illness
Infection is contracted via droplet or aerosol inhalation of infected water. Person to person spread is uncommon.
Effects range from asymptomatic seroconversion to a self-limiting mild febrile illness with headache, chills and myalgia to a severe potentially fatal progressive illness with malaise, myalgia, headache, a rapidly rising fever with rigors and a dry unproductive cough.
Progressively severe symptoms occurring within a few days include chest pain, often pleuritic in type, vomiting, diarrhoea, abdominal pain and distension. Central nervous system findings include confusion, delirium, dysarthria, neuropathy, and clouding of consciousness disproportionate to the degree of fever or clinical signs of infection.
Further prognostically unfavourable complications include disseminated intravascular coagulation, gastro-intestinal bleeding, rhabdomyolysis, respiratory failure, encephalopathy, shock and renal failure.

Diagnosis
Clinical suspicion in the presence of a suggestive illness with further confirmation by some or all of, direct fluoroscopy of bronchial secretions, sputum culture, fourfold rise in serum antibody levels, and urinary antigen assay.

Treatment
Erythromycin 2-4g day orally or intravenously sometimes accompanied by rifampicin. Supportive management is required, which may involve intensive care for all but the mildest cases.

Prevention
Regular cleaning and maintenance of water supplies, cooling and ventilation systems, use of biocides, bacteriological checks, and keeping the water supply temperature above 55-60C.
For the traveller, awareness of the risk, mode of infection and symptoms.
Flushing through showers in hotels or institutions with hot water when they have not been used recently may help.

Surveillance
There is a European surveillance scheme for travel related infections is in place which is 'triggered' by reports from Public Health Consultants and Laboratories. This aims to identify outbreaks early so that environmental health measures can be instituted promptly.

Recommended for further information
Oxford Textbook of Medicine, Third Edition, volume 1, sections 1-10, pages 722-728.