L. pneumophila serology?

I am about to see a young patient who has had a three months of upper respiratory symptoms without a fever. He was found to have the following L. pneumophila serological results: IgG-1: 128 (ref </=64), IgM-1: 512 (ref </= 256)


Others at his building have had similar symptoms. I only have info from a phone call and I have little additional information. The MD didn’t know if there was a fountain in the building lobby. I am suspicious regarding the diagnosis of Legionnaires’ in the “index case.” Any thoughts?


Surprisingly, this is not an uncommon problem, and we get this question occasionally. The missing info is whether he has ever had pneumonia in the past, especially within a year. It would also help to know the past medical history and the history of cigarette smoking.

Assuming that he has no overt history of pneumonia, this serology suggests that he has contracted Legionnaires’ disease and has either subclinical pneumonia or Legionella infection without pneumonia.  Assuming no other striking info comes from his PMH (including no antibiotic history); I would order a chest x-ray. It might be justifiable anyway given his prolonged duration of URI.

If it was negative, you have 2 pragmatic choices:

1) Give him empiric azithromycin 500 mg for 7 days

2) Have an ENT evaluate him for chronic sinusitis

(I had similar symptoms to this patient and didn’t use antibiotics for a likely viral URI. My cough exacerbated in the third month and I was moved to another room due to spastic coughing fits lying supine with copious rhinorrhea. I had a nasal endoscopy and laryngoscopy with the ENT rhinologist. [See CID article, Jan 2012] The endoscopic cultures revealed H influenza-beta-lactamase positive. I took Augmentin with clinical response in 3 days; I took my last dose of Augmentin last night and cough has disappeared.)

Based on the limited history, I would give empiric azithro. One reason is relief of anxiety for both referring physician and patient. (For the other employees with similar symptoms/anxiety about Legionnaires’ disease, I don’t believe that decorative fountains cause Legionnaires’ disease.)

When you get the remaining history, email me again. We have devised an inexpensive solution for buildings which are colonized with Legionella and are not healthcare facilities with high-risk patients. Example: hotels, dormitories, office buildings.