Reducing Legionella risk: a matter of simple maintenance?

A new Australian study has used a novel method in combination with standard detection methods to examine the effect of temporary water stagnation on Legionella and microbial communities present in a hospital water system.

A major challenge for Legionella management within large hospital systems is that under unfavourable conditions, Legionella transforms into a state (called viable but non culturable — VBNC) that cannot be detected using standard methods.

To understand the extent of the problem, Flinders University researchers conducted the first comprehensive study that quantified all Legionella, including those in the VBNC state, and free-living amoebae from a hospital water system under dynamic flow and temperature conditions.

“We took a different approach because we didn’t know how often the standard method was returning false negative results for Legionella and it’s really hard to determine the optimal management approach if you can’t trust your testing method,” said Flinders University’s Associate Professor Harriet Whiley.

Using a commercially available monitoring system developed by Enware Australia, the researchers measured water temperature, number and duration of water flow events for a sample of hand basins and showers. Their analysis demonstrated that 21.8% of samples were positive for Legionella spp., 21% for L. pneumophila, 40.9% for V. vermiformis and 4.2% for Acanthamoeba.

Temporary water stagnation arising through intermittent usage (being less than 2 hours per month) significantly increased the amount of Legionella.

“Temporary stagnation arising through intermittent usage causes water quality to deteriorate — and this study identified that temporary stagnation for over a month promotes the persistence of Legionella,” Whiley said.

“Similarly, free-living amoeba and heterotrophic bacteria present in this temporary stagnant environment were positively correlated with Legionella. All samples positive for Legionella were also positive for amoeba.

“Therefore, temporary stagnation and free-living amoeba must be managed for the proper control and prevention of Legionnaires’ disease.”

The study also found that the standard microbiological culture method used to detect Legionella returned a false negative result for 88% of the Legionella positive samples — highlighting a need for future research to investigate concentrations of Legionella that pose a risk to public health, in order to inform improved Legionella guidelines.

The research — ‘Stagnation arising through intermittent usage is associated with increased viable but non culturable Legionella and amoeba hosts in a hospital water system’ — has been published by Frontiers in Cellular and Infection Microbiology (Bacteria and Host section).

Image credit: iStock.com/Svitlana Hulko