Research shows that temperature control measures in hospitals need to be revised to control Legionella

New work has revealed important findings about the survival of Legionella pneumophila bacteria in hospital water systems. Recently published in the news Science of the total environmentthe study suggests adjustments in control policy to effectively combat legionellosis.

The study examined 80 isolates of Legionella pneumophila serogroup 6 from two independent hospital hot water systems, highlighting the genotypic variability and thermotolerance of the strains. Using flow cytometry to assess membrane integrity after exposing the bacteria to temperatures of 50°C, 55°C and 60°C for 24 hours, the team found that a significant percentage of the bacteria showed no growth on plate cultures, but in a viable but non-culturable state (VBNC).

Specifically, 52% of bacteria at 50°C and 23% at 55°C retained their membrane integrity, while at 60°C this was less than 5%. These findings underline the limitation of the plate culture method for detecting Legionella under thermal stress conditions.

The research team includes the Clinical and Environmental Infectious Diseases Study Group (CEID) of the German Trias i Pujol Research Institute (IGTP), led by Dr. Laura Gavaldà from Bellvitge University Hospital, in collaboration with Institut Català d’Oncologia and Barcelona Public Health Bureau.

Noemí Párraga, the first author of the study, emphasizes: “The plate culture technique for Legionella control, required by Spanish legislation, underestimates the presence of this bacterium under stress factors, as it can remain in a viable but non-culturable state. This condition can be reversed, thereby restoring the infectious potential of the microorganism.”

This study suggests the opportunity to improve detection methods to ensure a safe hospital environment, recognizing that Legionella can withstand legal temperatures and remain in a viable but non-culturable state. It is advisable to consider this subpopulation in assessments as it has the potential to become infectious.

“Increasing the temperature by 5˚C at the end points of hot water circuits could significantly reduce the number of cases of legionellosis, especially in centers with a high presence of people at risk,” says Dr. Gavalda.

In 2022, the new Royal Decree 487/2022 was published in Spain, which establishes the sanitary requirements for the prevention and control of legionellosis. This document sets out a series of measures for the prevention and control of Legionella in water installations. One of the defined measures is the temperature in hot and cold water circuits. A minimum temperature of 60°C is set in the accumulators and 50°C at the end points (taps and showers) and at the return. The minimum required by the current Royal Decree is microbiological controls via plate culture.

Dr. At the time of the study, Laura Gavaldà was a specialist at the Preventive Medicine and Hospital Hygiene department at Bellvitge Hospital. She is currently Head of the Tuberculosis Prevention and Control Service and of Specific Programs at the Public Health Agency of Catalonia.

Provided by the German Trias i Pujol Research Institute