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A mysterious illness made headlines in Philadelphia this month in 1976. The illness caused a serious type of pneumonia — 182 people got sick and 29 people died. Eventually, this illness would become known as Legionnaires' disease.

Forty years after that first outbreak, Legionnaires' disease is a growing health concern. Each year about 5,000 people in the United States are now diagnosed with Legionnaires' disease and there are at least 20 outbreaks. This disease is most commonly diagnosed in the summer months. Here are four key things you should know about Legionnaires' disease.

People who are 50 years or older are more likely to get sick if they are exposed to the bacteria that cause Legionnaires' disease. Other factors that can increase your risk include:

Fortunately, most healthy people do not get Legionnaires' disease after being exposed.

Like other types of pneumonia, signs and symptoms of Legionnaires' disease can include cough, muscle aches, fever, shortness of breath and headache. Most people with Legionnaires' disease need care in a hospital, but will fully recover with treatment. However, about one in 10 who get this disease will die due to complications from their illness.

Legionnaires' disease is caused by bacteria called Legionella that live in water. To get sick, people have to breathe the bacteria into their lungs. Legionella is usually spread through water droplets in the air (mist), but in rare cases people can get sick after contaminated drinking water is swallowed “down the wrong pipe” into the lungs.

The Centers for Disease Control and Prevention (CDC) reviewed the outbreaks it investigated over the past 15 years and found that certain types of buildings and water sources are more likely to be associated with a Legionnaires' disease outbreak. The most common places where people get sick are hotels, long-term care facilities and hospitals. In these types of buildings, the most likely sources for spreading water droplets contaminated with the bacteria include showers and faucets, cooling towers (parts of large, centralized air conditioning units), hot tubs and decorative fountains. Cruise ships are another place where Legionnaires' disease outbreaks can happen. CDC recommends building owners and managers use Legionella water management programs to reduce the risk of Legionnaires' disease.

When you see the doctor, mention any possible exposures to Legionella. Be sure to mention if you used a hot tub, spent any nights away from home, or stayed in a hospital in the last two weeks.

Talk to your healthcare professional about your risk of getting sick. You can also encourage owners and managers of the buildings where you live, work and get medical treatment to adopt a Legionella water management program.

  1. Certain people are at increased risk for Legionnaires' disease.
    • Being a current or former smoker
    • Having chronic lung disease, such as or chronic obstructive pulmonary disease (COPD)
    • Having a weakened immune system from diseases like cancer, diabetes or kidney failure
    • Taking medication that weakens your immune system
  2. Legionnaires' disease is serious but can be treated.
  3. Legionnaires' disease is caused by breathing in contaminated water.
  4. See a doctor right away if you develop pneumonia symptoms.

Learn more at CDC.gov/vitalsigns/legionnaires.

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