Hawke's Bay residents are being urged to see their doctor if they have symptoms of a stomach bug, after 45 people have been diagnosed - and one person admitted to hospital - with a "nasty" strain of the infection.
The cause of the Cryptosporidium, or Crypto, outbreak is not yet known, but health officials say it appears to be from more than once source.
Hawke's Bay District Health Board Medical Officer of Health Nicholas Jones said it was potentially spreading through day care centres, drinking untreated water, and swimming in pools, lakes and rivers.
Crypto is contracted from a parasite found in the gut of cattle and other animals and is passed to humans through contact with animals, contaminated water or food, or direct contact with human waste.The disease causes watery diarrhoea and stomach cramps, and may cause children to lose their appetite and vomit before the diarrhoea starts.
"Some people can have a very mild illness but it can be nasty," said Dr Jones. "Symptoms can come and go but have usually stopped within four weeks. In rare cases when a person's immune system is very weak the disease can go on longer and cause complications."