Q. Is it true that you can get Legionnaires' disease from gagging on a drink of water? This has got to be bogus.

While this sounds like an urban myth, it is true.

Most people become infected with Legionnaires' disease when they inhale microscopic water droplets containing Legionella bacteria. If you choke or cough while drinking, you can get water in your lungs. If the water contains Legionella, you may develop Legionnaires' disease, which is a form of pneumonia.

Legionnaires' disease primarily affects the lungs. However, it can cause infections in wounds and in other parts of the body, including the heart.

Those who are especially vulnerable to Legionnaires' disease are older adults, smokers, heavy drinkers and people with weakened immune systems.

If not treated, Legionnaires' disease can be fatal. Immediate treatment with antibiotics can usually cure Legionnaires' disease.

Legionella bacteria also cause Pontiac fever, which is like influenza. Pontiac fever usually clears on its own in a few days.

Legionnaires' disease got its name from American Legionnaires who were celebrating the nation's bicentennial in the summer of 1976 in Philadelphia. Hundreds became very ill and 34 died from the disease. The infection was traced to a hotel water system. It took almost six months to identify the bacteria that caused the illness.

This type of bacteria existed before the Philadelphia outbreak. More Legionnaires' disease is being detected now because doctors look for it whenever a patient has pneumonia. It is difficult to distinguish this disease from other forms of pneumonia; so many cases still go unreported.

The Legionella bacteria usually are found in water; they grow best when the water is warm. So, Legionella is often found in hot tubs, plumbing, water tanks, whirlpool spas on cruise ships and large air-conditioning systems.

A few people have contracted the disease after working in the garden or using contaminated potting soil. It's also possible that the disease may spread when earth containing the bacteria is stirred up at large construction sites.

Like many microorganisms, Legionella bacteria can attach to the insides of pipes, faucets and showerheads. Then they form a "biofilm." on the surfaces. As water flows past, it dislodges some of the biofilm and spreads bacteria through the water system.

You can get Legionnaires' disease in your home, but most cases have occurred in large buildings; there's a theory that extensive systems permit bacteria to grow and spread more easily.

Legionnaires' disease is a sporadic and local problem. It often occurs in hospitals and nursing homes where the bacteria can spread and the residents are vulnerable to disease. There is no evidence that the disease is transmitted between people.

Legionnaires' disease is common in the United States. About 25,000 cases of the illness occur each year and cause more than 4,000 deaths. The fatality rate is similar to that of other forms of pneumonia, which is about 15 percent.

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