Hundreds of people have been struck down by gastroenteritis with NSW Health urging affected people to stay home and follow medical advice.
There were 39 gastro outbreaks in NSW institutions between August 20 and 26, including 22 in childcare centres, 10 in aged-care homes, five in hospitals and two in schools.
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NSW Health said at least 348 people were affected by the bug in these outbreaks, which is more than double the previous five-year weekly average number of outbreaks for August.
Director Communicable Diseases, NSW Health, Vicky Sheppeard said it appeared the outbreaks were caused by viral gastroenteritis including rotavirus and norovirus which spread easily.
"Gastroenteritis is highly infectious so it's vital that those infected stay home from work and keep sick children home from school or childcare for at least 24 hours after the last symptoms have stopped," Dr Sheppeard said.
"If your work involves handling food or looking after children, the elderly or patients, do not return to work until 48 hours after symptoms have stopped.
"The best defence against gastroenteritis is to wash your hands thoroughly with soap and running water for at least 10 seconds before handling and eating food, and after using the toilet, changing nappies or assisting someone who has diarrhoea or vomiting."
Winter has been a bad season for gastro in Australia; 1900 people attended NSW emergency departments with the bug in early August.
Brisbane has also been affected by an outbreak, with 51 childcare centres hit in the eight weeks to August 14.
NSW Health said all children should receive the rotavirus vaccine for free as part of the National Immunisation Program.
The bug can cause nausea, vomiting, diarrhoea, fever, abdominal pain, headache and muscle aches lasting between one and three days.
These figure come after NSW Health data showed there were 35,670 confirmed flu cases in NSW last month, making it the worst month on record for flu cases in NSW.
