A potentially lethal strain of E.coli has been found in Irish beaches, rivers and lakes which are popular with bathers and deemed to have excellent water quality under EU standards.
Researchers say the bacteria, known as Shiga-toxigenic E.coli (STEC), can cause disease, severe intestinal infection, potentially renal failure and even death.
Ireland is the worst country in the European Union for STEC infection rates, suffering up to 10 times the European average.
In a study, led by Prof Dearbháile Morris and Dr Louise O'Connor at the School of Medicine in NUI Galway, academics tested water samples from the sea, rivers and lakes between December 2018 and October 2019.
River samples
All 75 sites are used by people for bathing and recreation. Some 49 – or 65 per cent – showed up positive for the presence of the disease-causing strain of the bacteria.
More than nine in 10 (93 per cent) of river samples were positive, as were three quarters (75 per cent) of lake samples and more than half (56 per cent) of seawater samples.
“There was a high occurrence of genetic markers for STEC in the samples tested, highlighting the need for further investigation to establish the scale of the problem, not only in Ireland but globally,” said Prof Morris.
“It is worth noting that all of the bathing waters tested were designated as of good or excellent quality based on current EU bathing water quality monitoring criteria.”
Under that criteria, bathing water quality is assessed on the estimated total number of E. coli in a 100ml sample between May to September.
Most E. coli are not harmful, but some like STEC can be poisonous.
"Bathing waters in Europe and elsewhere are not routinely monitored for the presence of STEC," said Prof Morris, who believes the research is the first of its kind in Ireland.
“This study highlights the limitations of only assessing the total number of E. coli present as an indicator of water quality without taking into consideration the potential pathogenicity of some variants.”
The research was due to be presented at the European Congress on Clinical Microbiology and Infectious Diseases in Paris this month, but the event was cancelled because of the Covid-19 pandemic.
The details of the 75 sites where water was sampled are not been published. They included 52 seawater samples, 15 river samples and 8 lake water samples.