SEVEN wards at a hospital have been hit by a virus that causes sickness and vomiting.

Dozens of elderly patients at York Hospital have been struck down with the Norwalk virus.

The infection is easily spread from person to person through the air.

Patients on the affected wards are being treated in isolation, and the wards have been closed to new patients.

Patients' relatives are being allowed on to the wards under caution.

The symptoms usually ease within 24 hours, but patients remain infectious for at least two days after recovery.

A York Hospitals NHS Trust spokesman said it was difficult to say how the infection had entered the hospital.

The spokesman said: "We get this virus every year at this time of year.

"It is a common virus in hospitals, nursing homes and schools, anywhere where you have a lot of people in one place.

"Our treatment varies from day to day and the number of patients affected varies as people get better and others catch the bug.

"We are undertaking extremely stringent infection control measures above and beyond those normally in place to get this outbreak under control."

Experts say the virus rarely causes long-term health problems.