There have now been 55 reported cases of a "nasty" strain of stomach bug hitting Hawke's Bay.
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.
A public notification on Monday alerted to 45 cases but yesterday that has risen to 55.
Hawke's Bay District Health Board Medical Officer of Health Nicholas Jones said the outbreak 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.
The illness ranged from mild symptoms to more sever, and usually lasted less than four weeks.
Dr Jones said hand washing is particularly important to help prevent the spread of the infection and for parents to keep sick children away from day care centres and school.
The Health Protection team continued to investigate all cases to establish whether there was a common source of the outbreak, but so far it looked like there was more than one source.
There was no evidence that city water supplies were causing problems.
Anyone with symptoms should visit their doctor, drink plenty of fluids, follow doctors instructions and return to the doctor especially if a child or adult was not drinking or symptoms persisted or worsened.