The are fastidious Gram‐negative bacteria that reside in aquatic environments. They are a cause of severe community acquired pneumonia. serogroup 1 is responsible for 70–90 % of human infection, with cases caused by some of the other 15 serogroups accounting for the rest. Most hospitals use the urinary antigen test for detection of legionellosis; however, this will only reliably detect serogroup 1.

Case presentation:

We report two cases of severe community acquired pneumonia in patients requiring extracorporeal membrane oxygenation, referred to our adult Severe Respiratory Failure Unit. Legionella urinary antigen was negative in both cases. As clinical presentation strongly suggested Legionnaires’ disease (LD), respiratory samples were sent to the reference laboratory for PCR, which confirmed non‐serogroup 1 in both cases. Case 1 was subsequently confirmed by culture and confirmed as serogroup 5. Case 2 was culture‐negative.


is an important pathogen. Recognition of the potential for non‐serogroup 1 strains to cause severe LD should prompt requests for further investigations including PCR in patients who present with suggestive symptoms when the urine antigen is negative. Reliance on the urine antigen test may result in a potentially serious under‐recognition of non‐serogroup 1 and lead to mis‐diagnoses and inappropriate antimicrobial treatment.

  • This is an Open Access article distributed under the terms of the Creative Commons Attribution License (http://creativecommons.org/licenses/by/3.0/).

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