The number of children seeking treatment for gastroenteritis at emergency departments has risen above usual levels, the Western NSW Public Health Unit said.

"A high number of children aged under five seeking treatment for the highly-contagious infection," the alert stated.

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Western NSW Public Health Unit manager health protection Priscilla Stanley said gastroenteritis was often spread by direct contact with an infected person.

"It spreads easily between people if they haven't carefully washed their hands after using the toilet or before handling food," she said.

"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."

Include nausea, vomiting, diarrhoea, fever, abdominal pain, headache and muscle aches.

They can take up to three days to develop and usually last between one or two days, sometimes longer.

People are encouraged to rest and drinking plenty of fluids if they have gastro.

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 childcare or school who develop vomiting or diarrhoea, should stay home for at least 48 hours after their symptoms have stopped," Ms Stanley said.

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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 spread of infection to others.

People who are not in school or childcare, do not prepare food for others or do not look after children or the elderly should stay home for at least 24 hours after symptoms cease.

Anyone recovering from gastroenteritis should avoid visiting hospitals and aged care facilities to avoid spreading the infection to those most vulnerable.

For more information visit NSW Health online.

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