September 15, 2003, 8:37 AM EDT
CHICAGO -- Outbreaks of Legionnaires disease are often blamed on germs
spewing from air conditioning systems in big buildings, but new research shows
home hot water pipes can also be a common source of the disease.
Legionnaires is a form of pneumonia caused by a bug that occurs naturally in
water. The latest work, combined with earlier studies, suggests the bacteria
often grow in the slimy gunk lining residential hot water pipes, and home water
may be responsible for about 20 percent of cases.
"The evidence suggests that the residential water system is an
underappreciated source of Legionnaires disease," said Janet Stout, a
microbiologist who heads that special pathogens lab at the Veterans
Administration Medical Center in Pittsburgh.
Stout presented her latest findings Sunday at a conference in Chicago of the
American Society for Microbiology.
Stout estimates that between 2 percent and 5 percent of the 600,000 pneumonia
cases requiring hospitalization in the United States each year are causes by
Legionella pneumophilia bacteria. The diagnosis is often missed because finding
it requires both a bacterial culture and a special urine test.
Her team set out to track the sources of Legionnaires infections reported to the
health departments in Allegheny County in Pennsylvania and Cuyahoga County in
Ohio. The families of 21 victims agreed to allow testing of their home water,
and the Legionnaires bug was found in 24 percent of them. Two of the patients
studied died of their infections.
The bacteria flourish at temperatures between 90 and 105 degrees. People catch
the germs by inhaling drops of water. This can occur while showering, washing or
even drinking, especially if people have swallowing difficulties and
accidentally aspirate water.
Most people exposed to the bacteria never get sick. Those who are susceptible
may include the elderly as well as people with diabetes or diseases that weaken
the immune defenses.
"The overall perception we have that drinking water in the home
is free of bacteria is a misconception," said Stout. "Although
Legionnaires is a naturally occurring organism in water, people should be aware
this is a potential source of disease."
People often keep the temperature in their hot water tanks set low to save
electricity and prevent scalding. To kill off the Legionnaires bacteria, Stout
recommends temporarily turning up the temperature to above 140 and running the
hot water outlets for a half hour. Since the bug quickly returns, this should be
done every two or three months, especially if people prone to the infection are
using the water. If the temperature is kept high, the bacteria return much more
slowly or not at all.
Another strategy is to let the shower run on hot for a few minutes before
jumping in. This flushes out some of the bacteria that have built up in the
Typically, Legionnaires is blamed on air conditioning systems and cooling towers
in large buildings, such as hotels and hospitals, where outbreaks can be
"Everybody has been so focused on hospitals," said Richard Miller, a
microbiologist at the University of Louisville. "Homes have always been in
the background, but they are clearly a risk factor."
Legionnaires can be treated with the antibiotic erythromycin. The disease is
found worldwide and does not spread from person to person. It was first
recognized after an outbreak at an American Legion convention in 1976 in
Philadelphia, where it made 182 people sick.
By: Medical Editor Daniel Q. Haney is a special
correspondent for The Associated Press.