The disease that laid many Havelock North residents low is under control, the Hawke's Bay District Health Board said today.
Speaking at a press conference, board chief executive Kevin Snee said there had been a reduction in new cases.
Dr Snee said in hindsight, there were cases that showed up before Friday "but it wasn't visible to the health system".
One person was still in ICU and was in a stable condition, while 17 people in total were in hospital.
Drinking water assessor Peter Wood said an indicator result found in a water tanker at Havelock North High School could be a false positive due to the difficulty of getting a clean sample.
Earlier the Hastings District Council said an e-coli indicator had been found in one of nine water tankers used to supply drinking water to Havelock North residents.
David Sinclair, an Auckland medical officer of health, said the council was considering connecting Havelock to Hastings' water supply.
The indicator test today "not unexpected" in such a situation, he said.
The health team had taken "a very professional approach" in handling the situation, he said.
The council made the decision to chlorinate the water supply and emailed the DHB to tell them about it. The DHB confirmed chlorination today was appropriate, the council water services manager Brett Chapman said.
The suspect water tanker had a sign placed on it as soon as the positive indicator test was received and the tanker was later removed.
It had been at Havelock North High School car park since Monday.
Residents were directed to the tankers by the Hawke's Bay District Health Board after thousands became ill from campylobacter in the water last week.
Those who took water from the site and still have it in containers were asked to dump it.
All tankers were made vandal-proof.
The tanker had been filled up in Hastings. Hastings mayor Lawrence Yule said the decision had been made to chlorinate the Hastings water supply immediately as a precaution, despite the majority of indicator tests returning negative.
The water from the other tankers had been tested and was clear, however the water in all the tankers was now chlorinated.