Legionella ‘hiding’ in treated water
February 22, 2011
BACTERIA that cause the deadly legionnaire’s disease can persist in drinking water even after it has been chemically treated, according to the results of research in Sydney that suggests a need for increased testing.
The bugs can hide inside amoebae – generally harmless micro-organisms resistant to chlorine disinfection – which may later burst to release pathogens, say University of NSW scientists.
The phenomenon could explain a rise in the disease despite filtration and disinfectants in public water supplies.
A microbiologist at the University of NSW, Jacqueline Thomas, began researching amoebae in drinking water after legionella was found in Nepean Hospital’s water system and a car wash in Victoria in May 2008.
”[We wanted] to find how legionella was growing and spreading through water systems even after extensive treatment with chlorine and other filtration methods,” she said.
In NSW, infections from the bacteria increased between 2004 and 2007 and have since stabilised. The young, elderly and people with compromised immune systems are the most susceptible to the infection.
Ms Thomas said identifying the extent to which drinking water contributed to legionella infections in NSW was difficult because of limited testing and poor tracing of infections to their environmental source. But the Centres for Disease Control and Prevention in the United States found legionella accounted for 29 per cent of all drinking-water-borne disease outbreaks in that country between 2001 to 2006.
State water utilities are not required to regularly test for amoebae or legionella in their treatment and distribution systems under the Australian Drinking Water Guidelines, which are set and reviewed by the National Health and Medical Research Council.
Ms Thomas and her colleague Nicholas Ashbolt found bacteria such as legionella can become more infectious living inside amoebae.
”They can actually grow and replicate quite well in there, and because amoebae are bigger organisms they are resistant to drying out from chlorine to a larger degree,” said Ms Thomas, who is completing her doctorate with the university’s Water Research Centre. ”The thing that was really surprising was just how frequently amoebae were detected across all types of drinking water systems. It was a lot higher than anyone in the water industry had anticipated.”
Sydney Water said it used adequate disinfection and managed its flow rates to avoid stagnant water and increased temperatures to minimise the growth of amoebae and legionella.
Drinking water is tested and monitored at every stage of the supply system, including after it is treated, in distribution pipes and at customers’ taps, a spokesman said.
But Ms Thomas found amoebae could also breed inside house pipes, shower heads and taps.
Ms Thomas’s review of international research is published in the journal Environmental Science & Technology.