Many elderly who became ill during the Havelock North water crisis are still suffering six months on.
More than 5000 people were struck down with gastro and at least 20 hospitalised after the town's water supply was contaminated with campylobacter in August.
A government inquiry looking into the cause of the outbreak and the response to it has been hearing from witnesses at the Hastings District Court for the past fortnight.
Hawke's Bay District Health Board (DHB) medical officer of health Nick Jones told the inquiry yesterday many were still suffering.
"We have some anecdotal evidence that in fact a large number of elderly deteriorated in terms of their functional status in their ability to cope at home and have never recovered," he said.
Dr Jones said the DHB had put forward a proposal to the Health Research Council (HRC) to carry out research, including identifying the number of people impacted long-term. Long-term impacts include poor gastro intestinal function and reactive arthritis.
He said the HRC had indicated they were interested in supporting the study.
Dr Jones said no one expected so many to become ill in the town and something that may have contributed to this was the fact residents in Havelock North drank contaminated water over a number of days.
He also told the inquiry that one of the key indicators when determining if the contamination was widespread was the high number of students absent from school. About 20 per cent were off sick with diarrhoea and vomiting when the DHB first began looking into a possible outbreak.
Dr Jones said checking absenteeism was an "entirely ad hoc attempt to try and validate our hypothesis" and that it would be helpful if the Ministry of Education had an absenteeism alerting system whereby health authorities were notified when large numbers of students were ill.
The inquiry has heard from more than 20 witnesses (mainly from Hastings District Council, Hawke's Bay Regional Council and the DHB), with final witness statements heard yesterday.
Counsel assisting the panel, which is chaired by former Court of Appeal Judge Lyn Stevens, will provide a summary in court on Wednesday. The panel will then begin drafting their report which is due by March 31.
The inquiry has heard the contamination was caused when water from Mangateretere Stream containing sheep faeces was sucked through the ground and into the town's drinking water supply on the outskirts of town.