So far this year, there have been 25 outbreaks of gastroenteritis reported to the Illawarra Shoalhaven Local Health District (ISLHD) - 22 of these were in childcare centres.

In the previous four years during the same period there was an average of 10 gastro outbreaks in childcare centres.

ISLHD public health director Curtis Gregory said the increase could be due in part to better reporting to public health units.

However he said it was important to take preventative measures to reduce the risk of infection.

"Viral gastroenteritis is usually caused by norovirus or rotavirus and is often spread by direct contact with an infected person," he said.

"It can spread easily between people if they haven't carefully washed their hands.

"The best defence is to wash your hands thoroughly with soap and running water for at least 10 seconds before handling and eating food, and always wash your hands after using the toilet, changing nappies or assisting someone who has diarrhoea or vomiting."

Symptoms of gastroenteritis include nausea, vomiting, diarrhoea, fever, abdominal pain, headache and muscle aches. These can take up to three days to develop and usually last between one or two days, sometimes longer.

"The main treatment for viral gastroenteritis is rest and drinking plenty of fluids," Mr Gregory said.

"Most people recover without complications, however viral gastroenteritis can be serious for infants, people with suppressed immune systems and the elderly."

Infants or children in child care or school who develop vomiting or diarrhoea, should stay home for at least 48 hours after their symptoms have stopped.

People whose work involves handling food, or looking after children, the elderly or patients, should not return to work until 48 hours after symptoms have stopped to avoid spreading the infection to others.

Mr Gregory said those recovering from gastroenteritis should also avoid visiting hospitals and aged care facilities to avoid spreading the infection to those most vulnerable.