Derriford Hospital has been steam-cleaning affected wards

Derriford Hospital in Plymouth now has only three wards closed due to the illness, which causes sickness and diarrhoea.

Managers are meeting later on Saturday to decide whether another ward can be re-opened.

The hospital has been steam-cleaning wards to prevent the Norwalk virus from spreading any further.

Staffing levels

Another Devon hospital affected by a Norwalk outbreak, Torbay Hospital, has also re-opened a ward, with one ward still closed to new admissions.

Two wards at the Royal Devon and Exeter Hospital have also been affected by Norwalk and are closed to new admissions.

Derriford Hospital said its staffing levels had not been affected by the outbreak.

Norwalk is always present in the general population. But in a hospital, where so many people with low immune systems are close together, it is easy for the virus to spread.

Infection control relies on acting quickly to isolate and clean wards whenever there is a suspected case of the virus.

All the hospitals are asking outpatients to turn up for their appointments as planned.

However, visitors are being urged to stay away for the time being, particularly if they have had flu or sickness recently.