Steve Pergam, MD, MPH, FIDSA: Legionella Infections in Immunocompromised Patients

Steve Pergam, MD, MPH, FIDSA, Hutchison Cancer Research Center, Seattle Cancer Care Alliance: Legionella micdadei is named after Joseph McDade who originally found Legionella so it's been around for a long time. But we've certainly been seeing it more in our immunocompromised population and I think that's partially because our diagnostics have gotten better, we do more cultures in patients so we can identify patients with Legionella. And I think our awareness of Legionella has gone up so we're focusing a little bit more on making sure we identify these patients. They can look a lot like other infections so they can have findings on a chest CT or a chest x-ray that can look like another type of infection and so it's really important, and 1 of the messages I try to get across to people is if you're dealing with immunocompromised patients, to really make sure you do cultures, so either do sputum or preferably even BAL in patients that have pneumonia and make sure you send it for Legionella cultures because you can't identify these non-pneumophila species by a typical urinary antigen test which is often sent in patients like this.

It's an interesting area because we focus a lot on Legionellosis in the general population, but the patients at highest risk are patients who have underlying immune deficiencies, or are receiving chemotherapy, or other treatments that really limit their ability to respond to normal infections. So they tend to be patients that we sort of describe as canary in the coal mine, the sort of ones that can identify a particular problem with a water system sometimes, and are the ones that sometimes show up first with particular with Legionella infections. And they're particularly interesting for us because they often have Legionella that are not typically described in other populations. So we see what are called pneumophila Legionella, so Legionella pneumophila serotype 1 is the most common in the US, and really around the world. But the pneumophila species like Legionella micdadei or Legionella longbeachae are actually sometimes seen in our population. So it's an interesting, different spin on Legionella that we usually don't talk about as much.

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