Why all the news about Legionnaires' disease?

Legionnaires' disease has been in the news a bunch this summer. An outbreak in New York City caused 12 deaths. A West Chester University employee was confirmed to be infected with the disease last month, Legionella bacteria were found in university cooling towers and then again in hot water systems at the university over the weekend.

What's going on?

Nothing all that unusual, frankly. The events at West Chester have not been linked.  Legionella bacteria exist naturally in water in the environment, especially when it's warm. Breathed in as mist or water vapor, they can cause pneumonia in a small percentage of people.

We just don't normally hear about these cases because – unlike the New York cluster – public health authorities typically are not able to link them together and, therefore, cannot find the source of contamination. Properly maintained cooling towers are disinfected regularly; an interruption in commerce sometimes makes the news, as it did at a GlaxoSmithKline plant earlier this month.

The Philadelphia Department of Public Health advised clinicians two weeks ago that "a typical summer increase" was being observed in the city, which by Aug. 18 meant 32 cases and three deaths. Statewide, there have been 200 confirmed cases and 16 deaths this year, according to the Pennsylvania Department of Health. The New Jersey Department of Health reported 94 cases and six deaths.

Legionnaires' disease has especially high name recognition locally, of course, because it was named for an outbreak during the 1976 Pennsylvania American Legion convention at the old Bellvue-Stratford Hotel in Philadelphia that ended up causing 29 deaths.

A quick overview:

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. The New York cluster that was traced to a single cooling tower this summer sickened at least 124 people and killed 12, all of them with existing medical conditions

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; the CDC offers specific advice on hot tubs.

If you have a lot of questions about Legionnaires' disease or the bacterium that causes it, you may find the answers here.

Read more about The Public's Health.