What Is Legionella?

Both the bacterium and the illness it causes, Legionnaires' disease, have especially high name recognition locally because they were named for an outbreak at the 1976 Pennsylvania American Legion convention in Philadelphia that caused 29 deaths.

How common is Legionella? The bacteria are found naturally in water. They grow best in warm water, like that found in hot tubs, cooling towers, large plumbing systems, and decorative fountains (but apparently not car or window air-conditioners).

How does it cause illness? People can get Legionnaires' disease from breathing mist or vapor containing the bacteria, typically during the summer. It is not spread from person to person.

How common is the illness? Fewer than 5 percent of people who are exposed get sick. Most who do are over 50; have underlying medical conditions, especially chronic lung disease; are former or current smokers; or have immune systems weakened by disease or immunosuppressive drugs.

Is the illness serious? It is a type of pneumonia, which can be dangerous. An estimated 8,000 to 18,000 people a year are hospitalized nationwide; most recover with antibiotics. A New York cluster that was traced to a single cooling tower this summer sickened at least 124 people and killed 12, all with existing medical conditions

But the public rarely hears about cases, because health officials typically are unable to link them to a source. There have been 200 confirmed illnesses and 16 deaths in Pennsylvania this year, most during the summer; New Jersey had 94 cases and six deaths.

How can illness be prevented? Water systems in which Legionella grow should be regularly maintained and disinfected. Individuals at high risk may want to avoid hot tubs, where high water temperatures make disinfection more difficult.

- Don Sapatkin

SOURCES: Centers for Disease Control and Prevention; Pennsylvania, New Jersey, Philadelphia, and New York City Health DepartmentsEndText