Scanning electron micrograph (SEM) depicted a grouping of Gram-negative Legionella pneumophila bacteria.
CDC/Janice Haney Carr.
Legionnaires’ (LEE-juh-NAIRS) disease, also known as legionellosis (LEEjuh-nel-O-sis), is a bacterial infection that can lead to a serious form of pneumonia (nu-MO-nyah), or inflammation of the lungs.
In 1976, more than 200 people attending an American Legion convention at the Bellevue-Stratford Hotel in Philadelphia, Pennsylvania, suddenly came down with a mysterious illness that caused high fever, chills, and a cough. Thirty-four people died from severe pneumonia. The illness, later named Legionnaires’ disease in memory of the convention attendees, was caused by a previously undiscovered bacterium that scientists called Legionella pneumophila (LEE-juh-NEL-uh new-MOH-fee-luh). The bacteria were found to be living in the hotel's air-conditioning system. Since the initial outbreak, several other species of Legionella bacteria have been discovered, some of which can cause a very similar but less serious disease. Although people hear about outbreaks of Legionnaires' disease in public places that affect many people at once, such as the 2014 outbreak in Portugal or the 2015 outbreak in the cooling towers of the Lincoln Hospital in the South Bronx, New York, outbreaks actually occur more frequently on a much smaller scale. The disease can even break out in homes.
Legionnaires’ disease is not spread from person to person. Legionella bacteria live and grow in warm, stagnant (still) water, such as that found in airconditioning systems, hot-water tanks, or whirlpool spas. People might become infected by breathing in the mist from contaminated water sources (for example, the vents of air conditioners at a hotel or the showers at a gym).
Legionnaires’ disease can be difficult to distinguish from other types of pneumonia. There are very specific tests for it, but before ordering these tests, doctors need to learn as much as possible about their patients. First, doctors ask patients about their general health and recent activities. This history helps determine whether the patient might have been exposed to Legionella bacteria. Doctors then perform a physical examination of patients and take chest x-rays to look for signs of pneumonia in the lungs. If a doctor suspects Legionnaires' disease at this time, more specific laboratory tests might be ordered, including blood tests, to determine whether the patient's body is producing antibodies * to Legionella bacteria. Cultures of fluids from the patient's lungs may be done. To perform a culture, a person's sputum is placed on special material called a culture medium. If Legionella bacteria are present in the sputum, the medium will help them grow so that the bacterium can be identified. A urine test can also help confirm the presence of infection. The disease is treated with antibiotics and usually requires a stay in the hospital. In the hospital, patients receive supportive care, such as oxygen if they are having trouble breathing and extra fluids to replace what has been lost during periods of high fever.
Some people with Legionella infection experience only mild symptoms of illness, whereas others may be hospitalized for several weeks. Afterward, they may continue to be very tired for several more months. Most people who become ill with Legionnaires' disease recover, but in people with chronic lung problems, Legionella can make the condition worse, leading to severe illness. Up to 30 percent of cases of Legionnaires' disease are fatal.
There is little that people can do to avoid becoming infected with Legionella. In public places, better maintenance of plumbing and air-conditioning systems, including regular inspection and cleaning, can help limit the growth of the bacteria. If there is an outbreak, government health teams step in to decontaminate the suspected source of the bacteria.
See also Bacterial Infections • Pneumonia
Freije, Matthew R. Protect Yourself from Legionnaire's Disease: The Waterborne Illness that Continues to Kill and Harm. San Diego, CA: HC Information Resources, 2011.
Mueller, Benjamin. “Legionnaires’ Bacteria Regrew in Bronx Cooling Towers That Were Disinfected.” The New York Times. October 1, 2015.
MedlinePlus. “Legionnaires’ Disease.” U.S. National Library of Medicine. http://www.nlm.nih.gov/medlineplus/legionnairesdisease.html (accessed November 17, 2015).
Centers for Disease Control and Prevention. 1600 Clifton Rd., Atlanta, GA 30329-4027. Toll-free: 800-232-4636. Website: http://www.cdc.gov (accessed November 17, 2015).
Legionella. Website: http://legionella.org (accessed November 17, 2015).
* chronic (KRAH-nik) means lasting a long time or recurring frequently.
* emphysema (em-fuh-ZEE-mah) is a lung disease in which the tiny air sacs in the lungs become permanently damaged and are unable to maintain the normal exchange of oxygen and other respiratory gases with the blood, often causing breathing difficulty.
* immune system (im-YOON SIStem) is the system of the body composed of specialized cells and the substances they produce that helps protect the body against disease-causing germs.
* AIDS or acquired immunodeficiency (IH-myoo-no-dih-FIH-shen-see) syndrome, is an infection that severely weakens the immune system. It is caused by the human immunodeficiency virus (HIV).
* cancer a condition characterized by the uncontrolled overgrowth of abnormal cells, which may be fatal.
* antibodies (AN-tih-bah-deez) are protein molecules produced by the body's immune system to help fight specific infections caused by microorganisms, such as bacteria and viruses.