Affected wards are being kept under observation

There have been no new cases at the Royal Devon and Exeter hospital over the weekend.

At Torbay Hospital, only one ward remains closed to new admissions.

There are still four wards closed at Plymouth's Derriford Hospital, with two others being kept under close observation to ensure the virus has not spread.

Infection control

The Norwalk virus causes sickness and diarrhoea.

The virus 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.