Legionnaire's Disease

Legionnaires (lee-juh-NAIRS) disease, also known as legionellosis (lee-juh-nel-O-sis), is a bacterial infection that can lead to a serious form of pneumonia (nu-MO-nyah), or inflammation of the lungs.


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Legionello pneumophila



Pontiac fever

Respiratory infections

What Is Legionnaire's Disease?

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 Legionnaire's 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 we often hear about outbreaks of Legionnaire's disease in public places that affect many people at once, such outbreaks actually occur more frequently on a much smaller scale. The disease can even break out in homes.

How Common Is It?

Between 8,000 and 18,000 cases of Legionnaire's disease occur in the United States every year. It is believed that many more may go undiagnosed because the symptoms are so mild that people do not seek treatment. An outbreak is most likely to occur in summer or early fall, but it can happen at any time. The disease can affect people of all ages, but people who are middle age or older, who smoke cigarettes, or who have chronic * lung conditions, such as emphysema * , may be at especially high risk. People with weakened immune systems, such as those who have AIDS * or cancer, or those who have undergone organ transplantation, also are at greater risk of contracting the disease.

How Does Legionnaire's Disease Spread?

Legionnaire's disease is not spread from person to person. Legionella bacteria live and grow in warm, stagnant (still) water, such as that found in air-conditioning 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).

Signs and Symptoms

Symptoms of Legionella infection can range from mild to severe. In fact, some people infected with the bacteria may show no symptoms at all. Those who do might experience high fever, chills, and a cough that usually produces sputum (SPYOO-tum), a mixture of thick, slippery mucus (MYOO-kus) and other material coughed up from the inflamed lungs and windpipe. Some people also have extreme tiredness, muscle aches, headache, shortness of breath, stomach pain, diarrhea, and loss of appetite. Symptoms typically begin within 2 to 10 days of exposure to the bacterium. Kidney problems also may occur. Legionella bacteria also have been found to cause a less serious disease called Pontiac fever, which is characterized by mild flulike symptoms, without signs of pneumonia.

* chronic (KRAH-nik) means continuing for a long period of time.

* 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.

* 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).

* 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.

How Do Doctors Diagnose and Treat the Disease?

Legionnaire's 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 a patient. First, doctors will ask patients about their general health and recent activities. This history will help determine whether the patient might have been exposed to Legionella bacteria. Doctors then will perform a physical examination of the patient and take chest X rays to look for signs of pneumonia in the lungs. If a doctor suspects Legionnaire's 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 also can 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.

An electron micrograph of the bacteria Legionella pneumophila is shown here. Worldwide, there are as many as 40 species in the family of Legionella bacteria. Photo Researchers, Inc.
An electron micrograph of the bacteria Legionella pneumophila is shown here. Worldwide, there are as many as 40 species in the family of Legionella bacteria.
Photo Researchers, Inc.

The CDC in Action

When Legionnaire's disease broke out at the American Legion convention in Philadelphia in the summer of 1976, theories about its cause ranged from swine flu to chemical poisoning to communist conspiracies against American veterans. As fears mounted, the U.S. Centers for Disease Control and Prevention (CDC) in Atlanta, Georgia, in cooperation with other federal, state, and local authorities, launched one of the largest joint disease investigations in history. Investigators looked at the possible sources of the outbreak and the ways the infection could have spread. Survivors were examined, bodies were autopsied, and specimens of air, water, soil, and various hotel materials were tested. Comparing tissue samples from people who had become infected with samples held in storage at the CDC, investigators were even able to link the Philadelphia cases to unidentified cases of illness dating back as far as the 1940s. Finally, in 1977, doctors isolated the culprit bacterium from the hotel's cooling tower, and federal authorities put in place new hygiene safeguards to limit future problems. The CDC continues to work today in disease prevention and control, addressing such wide-ranging topics as air pollution, water contamination, and unsafe working conditions and implementing educational programs and various other strategies to protect the health of Americans.

What Are the Complications of
Legionnaire's Disease?

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 Legionnaire's disease recover, but in people with chronic lung problems, Legionella can make the condition worse, leading to severe illness. Up to 15 percent of cases of Legionnaire's disease are fatal.

Can the Disease Be Prevented?

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



National Center for Infectious Diseases, U.S. Centers for Disease Control and Prevention, Office of Health Communication, Mailstop C14, 1600 Clifton Road, Atlanta, GA 30333. The website for the National Center for Infectious Diseases offers information on various infectious illnesses, including Legionnaire's disease.
Telephone 800-311-3435

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