Two Dunedin Hospital wards have been closed and infection control measures are in place following a gastroenteritis outbreak.
It was first detected on Monday last week with norovirus confirmed in two wards and a third is awaiting test results.
The Southern DHB has confirmed 15 patients and six staff have either had or currently have the virus.
Its chief operating officer Hamish Brown said they implemented infection and prevention control measures immediately to limit the spread, working alongside their Public Health team.
"Given the nature of these viruses, it's difficult to identify when or how it came into the hospital," he said.
"The affected wards are presently closed to visitors and we are not allowing any patients in or out of these wards."
These settings were being reviewed daily.
"We know that norovirus is the major cause of non-bacterial gastroenteritis, and can remain viable in the environment for up to 12 days.
"This means that our staff are using vigorous infection and prevention controls including PPE, as well as increased cleaning measures."
Symptoms include nausea, vomiting, abdominal cramps and diarrhoea, and usually began one to two days after exposure and lasted a similar amount of time.
Affected people must stay away from work, school or preschool until they have been symptom-free for at least 48 hours.