Legionella Epidemiologic and Environmental Risks

Purpose of Review Legionella bacteria cause Legionnaires’ disease (LD), a severe and potentially fatal pneumonia. Legionellosis has been increasing in the USA and in Europe. We reviewed the literature to describe host factors predisposing to LD, environmental factors facilitating Legionella proliferation, and transmission modes leading to legionellosis cases and outbreaks. Findings Men, smokers, and persons 50 years and older, or with chronic pulmonary or immunocompromising conditions, are at risk for LD. Stagnated water and warm water temperature promote Legionella growth. Most legionellosis cases result from exposure to aerosolized contaminated water from man-made water systems, including hot tubs and whirlpool spas; hot water systems in large buildings, hotels, and hospitals; and cooling towers. Summary Water management plans for hot water systems at hospitals, long-term care facilities, and large buildings are important to help prevent LD, and careful epidemiologic investigations remain essential in controlling and preventing legionellosis outbreaks.