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MCQs in Tropical Medicine

Rob Skelly DTM+H FRCP

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Answer 81 - Legionnaires' disease

Legionnaires' disease:
False a. can be acquired by drinking infected water
True b. smokers are more susceptible
True c. most cases are sporadic
True d. hyponatraemia is typical
True e. may cause rigors

Legionella pneumophila is a Gram negative bacterium which was first identified in 1976. It is found widely in water systems and is spread by droplet inhalation. Infection may be associated with inhalation of free-living amoebae, with large quantities of Legionella arriving inside the amoebae. Those at increased risk include elderly men, smokers and the debilitated. Outbreaks may occur in hotels and hospitals.

Many infections are asymptomatic. After 2-10 days' incubation, presentation is with fever, rigors, headache, myalgia, cough and breathlessness. Confusion and diarrhoea also occur.

Laboratory features include leucocytosis, hyponatraemia and raised liver transaminases. The organism is difficult to culture and the diagnosis is usually confirmed by the detection of rising antibody titres in the serum. It may take 2-3 weeks for serology to become positive. Occasionally Legionella antigen is detected in the urine or sputum.

Copyright: Rob Skelly 2006