COLUMBUS, Ohio -- People living in homes supplied by non- municipal water sources or in which there have been recent plumbing repairs may be at increased risk of contracting Legionnaires' disease, new research suggests.

Researchers here studied 146 adults hospitalized for Legionnaires' disease and 276 hospitalized control subjects matched by age, sex and general illness category. They found that the Legionnaires' patients were more than twice as likely as the controls to have non-municipal water supplies for their homes or to have had recent home plumbing repairs.

Further, the researchers found that the Legionnaires' patients were about twice as likely as the control patients to have electric hot water heaters in their homes (as opposed to gas).

"Several studies have shown that Legionella bacteria are present in home water supplies," said Joseph F. Plouffe, professor of internal medicine at Ohio State University and a

co-author of the study. "However, to our knowledge, this is the first published controlled study to quantify risk factors for acquiring Legionnaires' disease in the home."

Legionnaires' disease is an acute respiratory infection caused by the bacterium Legionella pneumophilia and accounts for at least 1 to 5 percent of all adult cases of pneumonia in the United States each year, Plouffe said. Symptoms include high fever, chills, muscle aches, headache, dry cough and diarrhea. Unlike most pneumonias caused by infectious agents, Legionella infections are not transmitted from person to person, but from contaminated environmental sources, Plouffe said.

"Legionnaires' disease can be transmitted by a variety of devices that produce a water aerosol, such as showers, faucets, humidifiers, whirlpool baths and medication nebulizers," he said.

Plouffe conducted this research with Walter L. Straus from the Centers for Disease Control and Prevention and the University of North Carolina; Thomas M. File, Jr., and Sara-Jane Salstrom from the Northeastern Ohio Universities College of Medicine; Harvey B. Lipman, Robert F. Benson and Robert F. Breiman from the Centers for Disease Control and Prevention; and Barbara H. Hackman from Ohio State.

Also assisting in the study was the Ohio Legionnaires' Disease Group, a group of 20 physicians and scientists from two urban counties in Ohio and the Centers for Disease Control and Prevention in Atlanta. The group's work was published in a recent issue of the Archives of Internal Medicine.

For their study, Plouffe and his colleagues studied 146 patients with Legionnaires' disease and 276 control subjects matched to the Legionnaires' patients by age, sex and general illness category. The study subjects were patients at 15 different hospitals in two Ohio counties. The researchers interviewed each subject about his or her health, behavioral patterns, exposure to water and use of devices that produce a water-aerosol, such as water pics, shower massage devices and humidifiers.

The researchers then inspected the home of each study subject. There they recorded information about the home's hot water heaters, showerheads, faucets, humidifiers, dehumidifiers, water softeners and hot tubs, if applicable. The researchers measured the maximum and minimum temperature of the home's water, as well as the water's chlorine concentration and pH. Last, they collected water from various sites in the home and tested it for the presence of Legionella pneumophilia.

The researchers found Legionella pneumophilia in 6 percent of the homes studied -- a prevalence similar to that shown in previous home water surveys. Of the three water heaters identified as carrying the bacteria, all were the electric variety.

"Our results suggest that some Legionnaires' disease cases are acquired in the home and that residential well-water use and disturbances of residential water systems during plumbing work may increase the likelihood of transmission," Plouffe said. "Although the Legionnaires' patients were more likely to have electric than gas hot-water heaters, the finding was confounded with water supply source -- that is, people with electric water heaters were also more likely to have non-municipal water in their homes. Therefore, we can't conclusively determine whether water heater type itself is associated with Legionnaires' disease risk."

The explanations for why these factors increase the risk of Legionnaires' disease are relatively straightforward, Plouffe said.

Unlike bacteria in municipal water supplies, which are generally removed by filtration and chemical disinfection, bacteria in natural water sources can only be eliminated through active intervention by the owner, such as private residential chlorination, he said. "These measures may be inconsistent or incomplete," he said.

"Legionellae exist in the biofilm on the inside of pipes. When you do plumbing work, you create pressure shocks that shake the pipes, loosen the biofilm and get the bacteria into the water," he said. "Plus, the heating element in electric water heaters is about a third of the way up the tank, whereas with gas water heaters, the flame is obviously at the bottom. In an electric water heater, the area below the heating element is going to be cooler because heat rises. That water may be at a temperature that's ideal for the growth of Legionellae."

Other risk factors for Legionnaires' disease identified by the study included smoking, working more than 40 hours per week and spending nights away from home.

"Our findings are compatible with the possibility that some Legionnaires' disease transmission occurs in the workplace," Plouffe said. "Our findings are also compatible with possible transmission by traveling, since persons who spent time away from home were at increased risk for disease."

These findings suggest that those at highest risk of developing Legionnaires' disease should limit their exposure to water aerosols after home plumbing repairs, Plouffe said. People at highest risk of developing Legionnaires' disease include smokers, transplant recipients, AIDS patients, and those with lymphoma or leukemia.

"If you have someone in the house who is immune- compromised, you should flush out the faucets and showers within the first couple of hours after any plumbing repairs -- while the immune- compromised person is not there," he said. "In addition, people who are immune-compromised should speak with their doctor about the temperature and chlorine levels of the water they use on a daily basis."

Contact: Joseph F. Plouffe, (614) 293-8733; Plouffe.1@osu.edu

Written by Kelly McConaghy Kershner, (614) 292-8308; Kershner.4@osu.edu

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