Legionnaires’ disease is a severe infection caused by Legionella species, primarily L. pneumophila. L. pneumophila is responsible for 90 percent of infections. The disease is a common cause of severe pneumonia that requires hospitalization.  Symptoms may include a high fever, chills, cough, muscle aches, headaches, and diarrhea. In the United States, it is estimated that about 8,000 to 18,000 people hospitalized each year due to Legionnaires’ disease, however only about 3,000 cases are reported to the CDC.

Legionella bacteria are usually found in water. The bacteria occur naturally in the environment, says the CDC, and grow best in warm water. Specific areas where you might encounter the bacteria include: cooling towers, hot tubs and whirlpool spas, hot water tanks, decorative fountains or pools, and large plumbing systems.

There are two different illnesses caused by the Legionella bacteria: Legionnaires' disease and Pontiac fever. Someone with Legionnaires’ disease has pneumonia, while a person with Pontiac fever has a non-pneumonia influenza-like illness that is milder. Pontiac fever and Legionnaires’ disease share similar symptoms: cough, shortness of breath, high fever, muscle aches, and headaches. But unlike Legionnaires’ disease, Pontiac fever goes away without treatment.

Legionnaires’ disease is hard to diagnose because it shares signs and symptoms with other conditions. Symptoms of the disease usually begin 2 to 14 days after a person is exposed to the bacteria. Lung infection is common with Legionella because the bacteria thrive in the warm, moist environment of the lungs.

Legionnaires’ disease is treatable. While most cases are successfully treated with antibiotics, patients often still require hospitalization. It can be fatal, and some people are more likely to become seriously ill after contracting the disease. This includes people over 50, smokers, people with a chronic lung disease such as COPD, and people with a weakened immune system.

Legionnaires’ disease has some complications, including respiratory failure, septic shock, and acute kidney failure are all complications associated with the disease. Early treatment with antibiotics is the best line of defense against complications.

The disease doesn’t spread from person to person. Instead, Legionnaires’ disease is contracted by breathing in mist, steam, or vapor that has been contaminated with the bacteria. More than 20 percent of cases of Legionnaires’ disease may be associated with recent travel. Legionnaires’ disease outbreaks have been linked to hot tubs and whirlpools on cruise ships, swimming pools, and water systems in hotels, hospitals, and nursing homes. The Mayo Clinic reports that smoking may actually increase your risk of developing Legionnaires’ if you’re exposed to the bacteria.

Legionnaires’ disease is preventable. The most effective way to prevent the infection is to make sure that water systems like cooling towers, spas, and pools are properly maintained and up to current health and safety codes. You can purchase pool test strips to verify that your water is properly maintained.