I have a patient in my ER as we speak/type who I suspect of having a Legionella infection. She is a 62 yr old lady who returned two weeks ago from a month stay in Sri Lanka. She has a fever which started 2 days ago. She also developed hallucinations, diarrhea and a cough. Her CRP is 350 (N range<10). Her X-ray showed an upper right infiltrate. Because of her travel history and clinical signs I suspect a legionella infection. However her urine antigen test (Binax) is negative. What kind of serotype can be found on Sri Lanka? PubMed shows only 1 hit (Ceylon Med J 2000) where only 1 out of 16 Legionella isolates was tested and yielded serogroup 1.
We agree the history is suggestive of Legionnaires’ disease. The urinary antigen is sensitive only for serogroup 1 which is the predominant serogroup in Hong Kong and Taiwan, so I suspect that it is also the predominant serogroup in Thailand. (But I could be wrong.) n Australia, Legionella longbeachae is quite common which would not be detectable with the urinary antigen test. There are species and serogroups of Legionella that are missed by the urinary antigen test as you indicate. The test is highly specific so that if it is positive, the patient has Legionnaires’ disease. Your microbiology lab should attempt to culture the sputum with selective Legionella media as described on www.legionella.org. Serology should be obtained today and later to confirm the diagnosis. A gram stain of sputum should be done. Legionella would present with numerous leukocytes, but no visible bacteria.
I would certainly cover this patient with an anti-legionella antibiotic such as azithromycin or levofloxacin. And then switch when a pathogen is definitively identified. Keep in mind Meliodosis if she has been in rural areas.