A hot water tank at Harford Memorial Hospital was the likely cause of an outbreak of Legionnaires' disease near Baltimore.

A hot water tank at Harford Memorial Hospital, near Baltimore, was the likely cause of an outbreak of Legionnaires' disease that killed three elderly patients and sickened two others, according to a report in the Baltimore Sun. The first case was discovered June 8 in the hospital's intensive care unit. The three victims died between June 26 and July 9. Because the first two patients had been discharged earlier, hospital officials had no reason to initially suspect that the facility was the source of the infection, according to Dr. Diane Dwyer, chief epidemiologist for Maryland.

Samples from the hospital's water supply were taken on July 1 by the Maryland state health department. About a dozen samples taken from the hot water tank and downstream outlets tested positive for the bacteria. The water supply for the hospital did not test positive, although small amounts of the bacteria are believed to have entered the facility through the water supply and multiplied in the warmth of the tank, Dwyer said.

On July 3, the hospital's water system was heated to 150µ F and flushed and chlorinated. In addition, the tank implicated in the deaths was taken off line. Hot water tanks can provide ideal conditions for Legionella bacteria to thrive, especially if the water temperature is kept below 120µF.

According to the U.S. Centers for Disease Control and Prevention in Atlanta (CDC), 20 to 60 percent of hospitals have Legionella bacteria in their drinking water. According to the CDC, an estimated 10,000 to 15,000 people get legionnaries' disease in the U.S. each year. About 5 to 15 percent of known cases have been fatal.