Hepatitis A is usually a mild illness in children with complete recovery and no ongoing health effects, but it affects teenagers and adults more seriously.
It is excreted through faeces and can be spread from person to person or by swallowing food or water that has been contaminated.
Symptoms in children usually include fever, an upset stomach and feeling tired and generally unwell, Perera says.
Many children don't show signs of the infection, but very occasionally they will develop jaundice - a yellowing of the skin and the whites of the eyes.
"If a parent is concerned that their child may have been exposed to hepatitis A infection and they are unwell, we ask that they stay away from school, childcare centres and social events and contact their doctor. Hepatitis A is diagnosed by a blood test."
Perera says more information would be made available to affected schools and families.
The best way to prevent the spread of the infection is careful hand washing with soap and proper drying, especially after using the toilet and before eating.
"Hepatitis A is an uncommon disease in New Zealand but to keep it that way we need to contain the spread, regular hand washing with soap and warm water then drying thoroughly is the simplest way to prevent spread," Perera said.