New hospital study says heat exchangers may act as Legionella reservoir
Heat exchangers installed in a hospital to conserve energy promoted growth of Legionella pneumophila in the hot water supply, according to a new study published today in Infection Control & Hospital Epidemiology, the journal of the Society for Healthcare Epidemiology of America.
The findings call for healthcare facilities to examine the maintenance and operations of energy recovery devices installed on their water distribution system to help prevent Legionella growth and minimize infection risk. Legionella can cause severe respiratory infections, such as Legionnaire’s Disease, in people with weakened immune systems.
“We were surprised to see the extent of the contamination in the heat exchangers,” said Michèle Prévost, PhD, principal investigator in this study. “Because these units can act as incubators for pathogens in hot water systems, the operation and maintenance of heat exchangers need to be reviewed to minimize these risks and prevent future outbreaks.”
Following two cases of healthcare-associated Legionella infections at a 400-bed university hospital in Sherbrooke, Canada, the hot water system was identified as the source of contamination. During the environmental investigation, 27 out of 34 water samples collected from taps demonstrated high levels of the Legionella bacteria. (88 percent of taps in one wing and 56 percent in the other). In addition, 7 of 8 samples taken directly from the heat exchanger had high levels of Lp. Researchers determined that the newly-installed heat exchanger, which was used to pre-heat the hot water, acted as a reservoir for Lp and contributed to the system wide contamination that led to the cases.
Maintaining elevated temperatures and water circulation within the hot water system can help limit the growth and persistence of Legionella by reducing biofilm and stagnation. However, many hospitals now face increased pressure to install energy and water conservation devices in order to meet high standards for environmental efficiency, such as LEED certification.
As a result of these findings, researchers suggest that energy recovery devices in hot water systems should be subjected to an infection risk assessment prior to installation as they may result in negative unintended consequences. They also note that hot water system operators should not rely on the passage of water through the water heater to prevent Lp from recirculating because brief exposure to higher temperatures may not be enough to inactivate certain strains of Lp that have been known to resist high temperatures.
Following review of the study results, the hospital decided to stop the use of the heat exchangers. The hospital’s energy savings in this case were estimated to range from $700 to $1,700 each month, compared to the $34,000 per episode estimated cost of Legionellosis hospitalization. Furthermore, Louis Valiquette, MD, chief of microbiology at the University of Sherbrooke, concluded, “No energy or water savings are worth a life.”