Doctors are being urged to be look out for a new virus, called parechovirus, that affects infants and has not been seen in Australia before.
About 20 babies have been diagnosed with the gastro and respiratory virus, which usually only causes fever, rash and diarrhoea but in severe cases can develop into hepatitis or encephalitis.
New South Wales Health says it has been notified of around 20 cases of parechovirus in children aged under 16 weeks.
The first cases of the disease were recorded more than a decade ago, with outbreaks seen in the United States, Japan and Europe.
Doctor Vicky Sheppeard from NSW Health says parents and doctors should be on the lookout for symptoms.
“They get quite sick quite quickly,” she said of victims.