Nosocomial L pneumophila Outbreak Attributed to Heat Exchanger Installation

Nosocomial legionellosis as a result of heat exchangers installed in a hospital in Sherbrooke, Canada.

Two patients were reported to have acquired nosocomial legionellosis at a 400-bed university hospital in Sherbrooke, Canada as a result of heat exchangers installed in the hospital, according to a study published in Infection Control & Hospital Epidemiology.1

According to Emilie Bédard, PhD, from the Department of Civil Engineering at Polytechnique Montréal in Montréal, Canada and colleagues, the 2 patients who acquired Legionella pneumophila serogroup 5 (sg5) were within a single wing of the university hospital. “Following the reported cases, 250 mL of first flush hot water were collected from 25 taps (baths and sinks) within wing A (300 beds) and from 9 taps within wing B (100 beds, supplied by a separate hot water system).” The investigation revealed the percentage of L pneumophila sg5 positive taps was much higher in wing A (88%) compared to wing B (56%).

Environmental and operational factors, including microbial load, contributed to the growth L pneumophila at the hospital.  Environmental factors included temperature, surface area, surface-to-volume ratio, and material type.  Operational factors included stagnation and low flow of water.

While the contamination observed in wing B was associated with recirculation deficiencies, the reason for L pneumophila sg5 proliferation in wing A was due to the type heat exchanger installed on the hot water system.

“Although physical characteristics of the heat exchangers were similar in the 2 wings, the piping diagram and operating conditions were different. Design and operation of hot water system should prevent L pneumophila proliferation and prevent the conditions in which amoebae-hosting biofilms develop,” the researchers concluded.

The limitations of this study included the following:

  • Because the hospital had an earlier outbreak of L pneumophila sg5 in 1995, it is possible that the strain existed continuously in the system until the 2014 occurrence.
  • Pulsed-field gel electrophoresis was not performed on the strains 1 year after the outbreak.
  • Decrease in the contamination could not be attributed to a particular action, as multiple actions were undertaken simultaneously to address the L pneumophila contamination.
  • Because heat exchangers were not initially suspected, they were not sampled during the outbreak.

“We were surprised to see the extent of the contamination in the heat exchangers,” said Michèle Prévost, PhD, principal investigator in this study, in a press release to the Society for Healthcare Epidemiology of America. “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.”2

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  1. Bédard E, Lévesque S, Martin P, et al. Energy conservation and the promotion of legionella pneumophila growth: the probable role of heat exchangers in a nosocomial outbreakInfect Control Hosp Epidemiol. 2016. doi: 10.1017/ice.2016.205 [Epub ahead of print]
  2. Hospital Hot Water System Promotes the Growth of Legionella pneumophila [press release]. Arlington, VA: Society for Healthcare Epidemiology of America; September 20, 2016.