Norovirus Cases

A suspected case of norovirus:

• a) Vomiting: Two or more episodes of vomiting of suspected infectious cause* occurring in a 24 hour period
• b) Diarrhoea: Two or more loose stools in a 24 hour period*
• c) Diarrhoea and vomiting: One or more episodes of both symptoms occurring within a 24 hour period *

*not associated with prescribed drugs or treatments and not associated with reaction to anaesthetic or an underlying medical condition or existing illness.

A confirmed case of norovirus:

a,b or c above with microbiological confirmation

Norovirus outbreaks

Suspected outbreak: two or more cases, as defined above, occurring in a functional care unit within the hospital without laboratory confirmation.
Confirmed outbreak: as above with laboratory confirmation

Suspected AND laboratory confirmed norovirus outbreaks should be reported.

In the absence of laboratory confirmation, the following criteria can be used as a rough indicator of a norovirus outbreak:

• 1) average duration of illness of 12 to 60 hours
• 2) average incubation period of 24 to 48 hours
• 3) more than 50% of people with vomiting, and
• 4) no bacterial agent found.

If you suspect that an outbreak was caused by norovirus but it does not strictly meet these criteria, it should still be reported. Please report each affected ward separately. For example, if there are cases on three wards or care units report three separate outbreaks. An outbreak is considered over when there have been no new cases for seven days. For example, if there are a series of cases, then a break for 10 days followed by more cases, please report two separate outbreaks.

An outbreak will be considered to be over if there are no new cases arising after seven days after the last case was considered to be symptom free.