Water testing can fail to detect Legionella: study

Flinders University experts have found that standard testing for Legionnaires’ disease — which can be fatal — is not always fail-safe.

To counter the problem, the environmental health and microbiology scientists have devised a method to test for the bacterium Legionella pneumophila, particularly when the bacteria is ‘hidden’ by environmental stressors such as heat or disinfectant in engineered water systems.

Legionnaires’ disease is a pneumonia-like infection caused by L. pneumophila when transmitted by inhalation or aspiration of contaminated water aerosols from water systems.

About 500 cases are reported a year in Australia, but many more may go unconfirmed, said the Flinders experts, after recently finding more than 40% of drinking water tested positive for L. pneumophila.

The Flinders University research, published online in Frontiers of Microbiology, found that the standard protocol to test for the pathogen Legionella is not always accurate under certain conditions and can result in false-negative results in the presence of environmental stressors.

Under conditions affected by low water nutrients, disinfectant and high temperatures, Legionella bacteria enter a state called ‘viable but non culturable’ (or VBNC) and are still alive and infectious — although they cannot be detected by standard testing, explained PhD candidate Muhammad Atif Nisar who conducted the study.

“As well, we found that the decontamination steps, which are part of the standard detection method, can actually cause Legionella to transform into this VBNC state in which they cannot be detected.

“To rectify this, we have developed a new method to study VBNC Legionella which otherwise would not be detected in environmental samples,” he said.

“People conducting water testing for Legionella may be getting false-negative results,” said co-author Associate Professor Harriet Whiley.

“This may lead them to wrongly believe that their system is free from Legionella or may lead them to have overconfidence in a particular control method.

“We hope this new method will lead to better control strategies to prevent Legionnaires’ disease,” she said.

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