September 22, 2016
3 min read

Legionella infections linked to device in hospital’s hot water system

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Researchers say two patients at a Canadian hospital likely contracted legionellosis from the facility’s contaminated hot water system.

An investigation launched after the patients were diagnosed showed a large percentage of water taps in two wings of the hospital were infected with Legionella pneumophila bacteria, as was the energy-conserving heat exchanger used to preheat hot water for one of the wings.

Clinical and environmental isolates cultured from the infected patients and different stages of the water system showed matching strains of L. pneumophila, indicating a relationship, according to Michèle Prévost, PhD, professor in the department of civil engineering at Polytechnique Montréal, and colleagues.

Testing of an earlier sample showed the hospital’s hot water system may have been contaminated for 20 years.

“We were surprised to see the extent of the contamination in the heat exchangers,” Prévost said in a news release. “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.”

Credit: CDC

This is an image of Legionella pneumophila, which colonized a Canadian hospital’s hot water system, leading to two patient infections.

Source: CDC

Investigation follows infections

Two cases of L. pneumophila infection were reported in August 2014 in a wing of a tertiary care hospital in Sherbrooke, Canada, in the year after the installation of two heat exchangers to conserve energy, according to Prévost and colleagues. One was a leukemia patient in the oncology ward, and the other was a cardiac patient in the ICU who spent time in two wings of the hospital. Nosocomial legionellosis was diagnosed after cultures of clinical samples from the two patients tested positive for L. pneumophila.

The investigation by Prévost and colleagues included taking first-flush samples from 25 taps in the hospital’s wing A and nine in wing B, which was supplied by a different water heater. Testing showed that 88% of the water taps in wing A and 56% in wing B were contaminated with L. pneumophila.

Further, all three water samples and four out of five swabs from the heat exchanger in wing A also tested positive for L. pneumophila, suggesting that the heat exchanger was a reservoir for the bacteria and played a role in infecting patients.

The same strain of L. pneumophila was isolated from a 1995 sample of the hospital’s water that was taken as part of a previous case investigation, leading Prévost and colleagues to hypothesize that it had been present for 20 years, although they were unable to prove that because samples were not taken each year.

After the hospital disinfected the hot water system by shocking it with high temperatures, no further cases of legionellosis were reported despite heightened surveillance. However, L. pneumophila was still detected in more than 45% of faucets and in the recirculation water in both wings 6 months after disinfection of the system.

The hospital eventually stopped using its heat exchangers. Prévost and colleagues said the devices are susceptible to opportunistic pathogens such as L. pneumophila and urged that operators of hot water systems should not rely on water heaters to inactivate L. pneumophila, which can adapt to survive the treatment.

“Design and operation of hot water systems should prevent [L. pneumophila] proliferation and prevent the conditions in which amoeba-hosting biofilms develop,” they wrote.

The high cost of infection

The CDC recently reported a fourfold increase in cases of legionellosis — including Legionnaires’ disease and Pontiac fever — in the United States from 2000 to 2014 and said most cases can be prevented by improving water system management.

High-profile outbreaks include the one in Genesee County, Michigan, where 91 people were infected and 12 died of Legionnaires’ disease in 2014 and 2015. The outbreak coincided with the city of Flint switching from the Detroit water system to the more corrosive Flint River to save money. The water quality has improved since the city switched back to the Detroit water system in October 2015, researchers have said.

As of 2015, fewer than 100 cases of Legionnaires’ disease were reported each year in all of Canada, although the actual number is thought to be higher, according to the country’s public health agency.

Not only is legionellosis associated with a high mortality rate, but treating an infected patient can cost $34,000, according to Prévost and colleagues. Comparatively, they said the hospital in their report was saving between $700 to $1,700 per month on energy costs before it stopped using its heat exchangers.

Prévost and colleagues said hospitals that are considering using devices such as heat exchangers also should be willing to assess the risk for infection among its patients.

“The addition of energy conservation devices and operational procedures should be evaluated by the water safety committee together with the infection prevention and control team, and weighed against the risk of exposing patients and the burden of preventive monitoring,” they wrote. - by Gerard Gallagher

Disclosure: The researchers report no relevant financial disclosures.