An amoeba which causes a rare but painful disease involving severe ulcerations of the cornea and which sometimes leads to blindness has been found lurking in cold water tanks of people who have contracted the disease.

Contact lens wearers are most likely to contract the disease and researchers think that washing your face while wearing lenses could increase your chances of getting the potentially blinding eye infection.

Only around one in 30,000 contact lens users in the UK contracts the disease. But this rate is 15 times as high as in the US, and seven times as high as it is in the Netherlands and this lead researchers to suspect something was amiss with British plumbing systems.

At one time building regulations in the UK required all homes to have a cold water tank as a protection against back-contamination and for storing water against supply interruption. Typically this was a cold water tank in the loft and the only room in the house to have a non-tank supply was the kitchen sink. Even today this scheme is still built into many British homes although the regulations no longer require it. Elsewhere, the use of double check valves and pressurised hot water systems has eliminated the need for open storage tanks.

John Dart, an ophthalmologist at Moorfields Eye Hospital in London suspected that because the water in these tanks is stagnant, the tanks could be a breeding ground for the amoeba.

Dart and his colleagues analysed the DNA of the amoeba found in eight patients and in their water supplies. In six of these cases the organisms were identical, indicating that the water supply was the source of the infection.

Dart believes the greatest risk comes from washing while wearing lenses or handling lenses with wet hands. He recommends that people keep tap water away from their eyes when they are wearing contact lenses.