A group of canoeists who were boating on the River Liffey near Dublin are feared to have contracted the potentially-dangerous rat-borne Weil's disease.
One of the seven has been confirmed as having the infection and tests are being carried out on the others. The scare has prompted health officials to warn people against swimming in or boating on the Liffey.
Dr Marie Laffoy of the Eastern Health Board said: "We want to know about anyone who was on or in the river on or around October 13 and has since come down with flu-like symptoms. It can be treated quite easily with antibiotics.
"Weil's is a bacterial condition, which is not common here at all. It can cause high fever, severe headaches, chills, muscle aches, jaundice and abdominal pains. If it is not treated, it can go on to cause other more severe complaints, like kidney and liver conditions and respiratory disorders. That's why it is so important to treat it early. We want people to be aware that there is a risk, even if it is a very small one."