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Legionnaires' Disease on the Rise in the United States

OCT 23, 2017 | KRISTI ROSA
Over the last few years there have been several high-profile outbreaks of a particular infectious disease: Legionnaires.'

Although the disease was first described over 40 years ago, in a recent ID Week 2017 presentation, Laura Cooley, MD, MPH, from the Respiratory Diseases Branch of the Centers for Disease Control and Prevention (CDC), referred to it as an emerging disease in the sense that the number of recorded cases of Legionnaires’ in the United States continues to increase.

Why the increase? Dr. Cooley admitted that a solid answer remains elusive, but she postulated that it’s probably multifactorial. “There is definitely an increase in the susceptibility of the population in the United States. The population is aging, and there are more and more people on immunosuppressive medications,” Dr. Cooley shared.

She also pointed out that there could be more Legionella in the environment—with warmer temperatures making a great habitat for bacterial growth. Aging infrastructure could also encourage biofilm and Legionella growth. Dr. Cooley pointed out that improved diagnostic capabilities with the introduction of the urinary antigen test (UAT) for respiratory infections could also be a contributing factor; however, she feels it’s more so that “more clinicians are aware that this is a problem” thanks to the large outbreaks that have sprung up over the past years.

“There’s been political attention to the disease [as well as] media attention, and so, I think it’s a combination of this increase in cases and really big outbreaks that shifted our priorities and really encouraged our engagement,” Dr. Cooley said.

A recent analysis of 27 outbreaks that occurred between 2000 and 2014, found that the most common settings for Legionnaires’ outbreaks were hotels, long-term care facilities, and hospitals. The most common sources were potable water sources, such as showers and sinks, followed by cooling towers, and then hot tubs and decorative fountains. Dr. Cooley said that outbreak size differences were noted by source and by setting. For example, cooling tower outbreaks “were typically larger,” with a median of 22 cases per outbreak, versus potable water outbreaks, which were half as big—a median of 10 cases per outbreak.

Influenza A (H3N2) has caused most of the illnesses in this severe flu season, but influenza B is becoming increasingly responsible for more infections as the flu season continues to hit the United States.