Taranaki District Health Board is urging rural communites to be on the alert for bacteria carried in by cattle that can be passed on to humans.
Verotoxin-producing E coli is a bacteria carried in the intestines of cattle, which when passed onto children can cause severe gastroenteritis.
DHB medical officer of health Jonathan Jarman said children on farms were at a high risk of catching the disease, with nearly half of cases ending up in hospital.
Some children might suffer from far more serious side effects, he said.
"Young children with VTEC illness are more likely to get a severe complication called Haemolytic Uraemic Syndrome (HUS) which could damage their kidneys. On average we get a child with this complication once a year in Taranaki," he said.
"We've already had one case in April where a very sick child ended up needing further treatment in Auckland."
Dr Jarman said the bacteria could be passed on by drinking unpasteurised milk, eating contaminated food and swimming in water where you could not see your feet.
But the main source was through contact "with animal faeces onto your hands and into your mouth," he said.
"In fact that's our, really our main advice is to stress the importance of hand washing."
Symptoms include watery diarrhoea, blood in the diarrhoea, severe stomach pains, vomiting.