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Study finds environmental tests help predict hospital-acquired Legionnaires' disease risk

August 23, 2007

A new study spearheaded by the University of Pittsburgh School of Medicine has determined that environmental monitoring of institutional water systems can help to predict the risk of hospital-acquired Legionella pneumonia, better known as Legionnaires' disease. Reported recently in the journal Infection Control and Hospital Epidemiology, the 20-hospital study also calls for reconsideration of the current national infection-control policy to include routine testing of hospital water systems for Legionella, the bacterial group associated with Legionnaires'.

"Only those hospitals that had high levels of Legionella bacteria in their water systems had patients who contracted Legionnaires' disease," senior author Victor L. Yu, M.D., professor of medicine at the University of Pittsburgh School of Medicine, said of the study, which involved hospitals in 14 states. "Proactive monitoring of the hospital water supply alerted physicians to the hidden risk of Legionnaires' disease for their patients."

Legionella bacteria first were identified as causing pneumonia in 1976 following an outbreak among attendees at an American Legion convention at a Philadelphia hotel, resulting in the name Legionnaires' disease. With an average fatality rate of 28 percent, Legionnaires' is estimated to be responsible for up to 20,000 cases a year in the United States, many of them hospital-acquired. Currently, the U.S. Centers for Disease Control and Prevention recommends that hospitals and other health care institutions monitor patients for pneumonia incidence before doing environmental surveillance of water systems that can harbor the bacteria.

"Based in part on our work, and in collaboration with the Allegheny County Health Department and the Three Rivers Association for Professionals in Infection Control, the development of proactive guidelines for hospital-acquired Legionnaires' disease prevention has led to the virtual disappearance of this infection in Pittsburgh," said study first author Janet Stout, Ph.D., research assistant professor in Pitt's department of civil and environmental engineering. "We first reported the connection between hospital water supply and these infections in 1982."

For this investigation, Drs. Yu, Stout and colleagues evaluated samples of hospital system water at 20 facilities across the country from 2000 to 2002. Water samples were retrieved from at least 10 separate sites at each hospital on multiple occasions over the two-year period. When cases of Legionnaires' were identified, patient urine and sputum samples from 12 of the hospitals were tested to determine classification of Legionella, which has at least 48 strains.

The researchers found that 14 (70 percent) of hospital water systems tested positive for Legionella species, and that six (43 percent) positive hospitals had high-level colonization. Legionnaires' cases were among the 633 patients with hospital-acquired pneumonia whose urine or sputum samples were tested for Legionella bacteria. All were traced to hospitals with high-level colonization.

"Our study provides much-needed evidence to support a national policy change to include routine environmental surveillance of health care facility water systems along with stringent clinical monitoring of patients," said Dr. Stout, who estimates that 39,000 people have died of Legionnaires' since 1982. "We think this long overdue approach should be adopted by infection control and infectious disease practitioners nationwide."

University of Pittsburgh Schools of the Health Sciences