A gastro outbreak which has hit hundreds of people in Havelock North may have been caused by animal faeces entering the water supply, the district health board says.
The gastric illness, caused by a waterborne campylobacter infection, has left two people in critical condition in hospital, and may be linked to the death of an elderly rest home resident.
Medical officer of health Nick Jones told Morning Report 51 people had come into the Hawke's Bay Hospital's emergency department since the outbreak began late last week, and there had been around 280 notifications of gastroenteritis over the weekend.
However Dr Jones said those cases were only the ones the GPs had notified them of, and suspected there were many more.
He said there had been a lot of testing of faecal samples and they indicated campylobacter was present, suggesting that excrement from an animal may have entered the water supply.
"There's other things potentially that might be in there as well, and some of those are not going to be destroyed by chlorination so we're being a bit extra cautious and recommending that people boil their water."
Dr Jones said the contamination may have got into the groundwater itself, but the Hastings District Council wasn't sure how it had happened.
"My understanding is that the well goes down 20m, obviously that's a long way from the surface, so there's a lot of questions there to be answered about how it got in."
While there was concern in the community that the disease was contagious, Dr Jones said the illness wasn't easy to catch from another person, but encouraged people to wash their hands thoroughly after preparing food and using the toilet.
Third case of water contamination in Havelock North
It is the third case in three years of bacterial contamination in Havelock North's water supply coming from bores, after E coli was discovered in the water in 2013 and 2015.
But Hastings mayor Lawrence Yule said the bores which appeared to be contaminated this time had not been affected in the past.
If the bacteria in the water was found to be campolybacter, the council would remove its boil notice as chlorinating the water would be dealing with the problem, Mr Yule said.
However if it was E coli, and the source could not be found and eliminated, the Hastings District Council would have to permanently treat the bore system, or move the source away from the bores to another part of the Heretaunga Plains.
Mr Yule said there would be a full investigation of the contamination, as it must never happen again.
Pharmacies and medical centres in Havelock North have been inundated with enquiries since the outbreak, and the boil water notice for Havelock North residents remains in place.
Two private schools - Iona College and Woodford House - have been forced to close today because many staff and students have fallen sick, and won't reopen until Wednesday.