Viral gastroenteritis is caused by a number of different viruses, such as rotavirus and norovirus, and is spread by the vomit or faeces of an infected person through contaminated objects, food or drink and touching.

Outbreaks increase in winter and are common within families and group settings such as nursing homes, hospitals, child-care centres and schools.

Between March and May this year, 255 people presented to St George Hospital with gastroenteritis, compared to 219 presentations for the same time last year.

At Sutherland Hospital, the number of people who presented with the infection between March and May this year was 91, compared to 95 for the same period last year. Viral gastroenteritis can affect people of all ages and has no specific treatment, other than rest and drinking plenty of fluids.

On June 11, about 20 residents at a St George nursing home came down with the bug.

A spokeswoman for the Department of Health and Ageing said the matter was reported to the NSW Public Health Unit by the nursing home and that the Aged Care Complaints Investigation Scheme was also contacted by a relative of a resident at the home.

The CEO of the company that operates the nursing home said it had taken the necessary steps to contain the infection and that only about five residents were still sick. She said no patients had been hospitalised.

A spokeswoman for the South Eastern Sydney and Illawarra Area Health Service denied claims that an extra ward had been opened up at St George Hospital for gastroenteritis patients.

A diagnosis of viral gastroenteritis is usually based on a person's symptoms; however, stool samples will be taken during outbreaks.

Details: Public Health Unit, South Eastern Sydney and Illawarra Area Health Service, 93828333.