Legionnaires’ disease is an acute respiratory infection and pneumonia caused by the Legionella bacterium, first identified as the cause of an outbreak of severe pneumonia during an American Legion convention in Philadelphia in 1976.

Between 8,000 and 18,000 people are hospitalized with Legionnaires’ disease each year in the United States, but the number of cases may be higher since many infections are not diagnosed or reported. Although more cases are discovered in summer or early fall, the disease can occur any time of the year. Most patients can be treated with antibiotics, and healthy individuals usually recover completely, but the illness can be very serious and causes death in 5 to 30 percent of cases.

Legionella is found naturally in the environment and thrives in warm water like that in hot tubs, cooling towers, hot water tanks, large plumbing systems or air conditioning systems of large buildings. It does not seem to grow in car or window-type air conditioners. People get Legionnaires’ disease when they breathe in mist, vapor or microscopic droplets of water that are contaminated with the bacterium.

For years, outbreaks have been identified among patients in hospitals, possibly because hospital buildings have complex water systems and most of the patients already have illnesses that increase their risk for infection. Outbreaks have also occurred on cruise ships and in hotels and resorts. In Australia and the United States, rare cases have been related to exposure to potting soil. The largest outbreak (449 cases) was traced to a cooling tower on the roof of a city hospital in Murcia, Spain, in 2001.

Despite the presence of Legionella in many aquatic environments, the risk of developing the disease is low. Nonetheless, travelers should be aware of potential exposure during recreation in or near a whirlpool spa, while showering in a hotel or touring in cities with buildings that have cooling towers. Patients often do not recall specific water exposure, as it frequently occurs during activities of daily living.

Most infections occur in middle-aged or older people. The disease has been reported in children but typically is less severe. Legionnaires’ disease is an “opportunistic” disease that attacks individuals with an underlying illness. Most susceptible are those with kidney failure, diabetes, cancer, a weakened immune system or long-term chronic lung disease, as well as those with long-term use of a mechanical ventilator or medications that suppress the immune system such as chemotherapy and steroids. Alcoholics and cigarette smokers are also at greater risk.

The symptoms of Legionnaires’ disease are similar to other forms of pneumonia, which can make it difficult to diagnose, and include high fever, chills, cough, chest pain, shortness of breath, loss of energy, joint pain and lack of coordination. Symptoms usually begin within two to 14 days after exposure to the bacterium. Some individuals may also experience muscle aches, a general discomfort and headaches. Chest X-rays will indicate the presence of pneumonia; and tests on sputum (phlegm), blood and urine will show evidence of the bacterium.

Pontiac fever is a milder infection caused by Legionella. The symptoms usually last two to five days and include fever, headaches and muscle aches; there is no pneumonia. Symptoms may go away without treatment and without causing further problems.

If you believe you were exposed to Legionella, contact your health care provider or local health department. Indicate if you have traveled in the last two weeks and where you stayed. A person diagnosed with Legionnaires’ disease in the workplace is not a threat to others who share office space since it is not transmitted person to person.

Treatment (with quinolone and macrolide antibiotics) is started as soon as Legionnaires’ disease is suspected, without waiting for lab confirmation. Other supportive care includes fluid and electrolyte replacement and oxygen by mask or ventilator to assist in breathing and oxygenation. Early treatment reduces the severity of the symptoms and improves chances of recovery. The death rate for patients who develop Legionnaires’ disease while in the hospital is close to 50 percent, especially when antibiotics are started late.

Outbreaks of Legionnaires’ disease are preventable but require meticulous cleaning and disinfection of water systems in hospitals, hotels, nursing homes, cooling towers, pools, decorative fountains and whirlpool spas and hot tubs. From June 21 to July 4 this year, six cases of Legionnaires’ disease were traced to the Aria Resort in Las Vegas. All six patients were treated and fully recovered. According to the hotel, water tests detected elevated levels of the bacterium in several guestrooms, and they have remedied the problem.

There is no vaccine for the disease, and antibiotic prophylaxis is not effective. Travelers at increased risk for infection should avoid high-risk areas such as whirlpool spas. If exposure cannot be avoided, seek medical care at the first sign of symptoms. Avoiding smoking is the single-most important thing you can do to lower your risk of infection. For more information, visit www.legionella.org.

The content of this article is for informational purposes only. It is not intended to be a substitute for professional medical advice, diagnosis or treatment. Always seek the advice of your physician or other qualified health care provider with any questions you may have regarding a medical condition.