Q. What is Legionnaires' disease?
A. Legionnaires' disease is an acute, respiratory infection caused by the bacterium Legionella. An outbreak of this disease in Philadelphia in 1976, largely among people attending a state convention of the American Legion, led to its name.

Q. What are the usual symptoms?
A. Symptoms commonly include headaches, fatigue, weight loss, body aches, and fever. Non-productive cough, abdominal pains, and diarrhea occur in many patients. In patients with Legionnaires' disease, pneumonia develops which can cause death. With Pontiac fever there is no pneumonia, but the patient may have a high fever for 2-5 days and then recover without treatment. Legionellosis commonly occurs in patients who are elderly, immunocompromised, or otherwise in poor health.

Q. Is the illness always severe?
A. Studies have shown that about 5% to 15% of known cases of Legionnaires' disease have been fatal. However, many people may be infected with the bacterium causing Legionnaires' disease without developing any symptoms. Others may be treated without having to be hospitalized. Recent information suggests that many cases of Legionnaires' disease go undiagnosed.

Q. How is the disease diagnosed?
A. Your physician can order tests to confirm the diagnosis of Legionnaires' disease. The most useful tests include culturing the bacteria from sputum, detecting the presence of bacteria in a urine sample, and comparing antibody levels in two blood samples collected three to six weeks apart.

Q. Is there effective treatment for Legionnaires' disease?
A. The currently recommended drug of choice is erythromycin, which appears to be effective in treating the disease. Other drugs are available for patients unable to tolerate erythromycin.

Q. How is Legionnaires' disease spread?
A. There is no evidence for person-to-person spread of the disease. Most people contract Legionnaires' disease by inhaling mist that comes from a water source (e.g. showers, cooling towers, whirlpool baths) contaminated with Legionella bacteria. In some cases, the disease may be transmitted by aspirating contaminated water. Hot water distribution systems are commonly contaminated with Legionella.

Q. Who gets Legionnaires' disease?
A. People of any age may get Legionnaires' disease, but the illness most often affects middle-aged and older people, particularly those who smoke cigarettes or who drink heavily. Also at risk are people whose immune system is suppressed by diseases such as cancer, kidney failure requiring dialysis, diabetes, AIDS, chronic lung disease, or heart failure. Those who take drugs that suppress the immune system such as prednisone, azathioprine, or cyclosporine are also at higher risk.

Q. Are air conditioning systems a potential source of spread?
A. The bacterium has been found in cooling towers and evaporative condensers of large air conditioning systems. Such systems have been associated with outbreaks of disease.

Q. Where is the disease found?
A. Cases have been identified throughout the United States and in several foreign countries. It likely occurs worldwide.

Q. How common is Legionnaires' disease in the United States?
A. It is estimated that around 10,000 people develop Legionnaires' disease each year in the United States. An additional unknown number are infected with Legionella bacteria but have only a minor illness or no illness at all. The disease can occur in outbreaks or as single cases.