Six cases of E. coli are being investigated in Co Sligo by the Health Services Executive.
The Departments of Public Health and Environmental Health are working to identify the source of the infection.
There are concerns about a possible association between the infections and people who had been in Enniscrone, Co Sligo between 20 July and 20 August, 2007.
The HSE states that the investigation is in the early stages and no conclusive findings have yet been made.
As a precautionary measure, the HSE would like to identify anyone who visited, stayed in, or ate food in Enniscrone, Co Sligo between 20 July and 20 August and who subsequently became ill with diarrhoea or vomiting or abdominal pain.
All of these people are requested to contact the HSE helpline at 1890 200 548. The helpline will be open from 4pm to 8pm today and 9am to 6pm everyday until Friday 31 August.
According to the HSE, E. coli is a cause of gastroenteritis that may lead to vomiting and diarrhoea and sometimes severe abdominal pain.