Some victims of the Havelock North water contamination bugs could have been infected as early as six days before the alarm was raised, the Hawke's Bay District Health Board reported.

The possibility was raised by DHB chief executive Dr Kevin Snee who said of the 523 on the list of definites and probable campylobacter patients there were some who believe they had symptoms as early as August 6.

Unaware of any concern at that stage, the council's routine tests of the Te Mata aquifer bores three days later, on August 9, raised no issues with E. coli bacteria, and it was not until three days later when a show of bacteria in new tests and a rocketing number of health cases led to the alert.

There were moderate presentations at the Hawke's Bay Hospital Emergency Department during the week, escalating to 13 on August 12, the Friday the alarm was raised and mainly after 6pm, and peaking at 27 the next day.

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It had tapered off to 14 a day during last week, 12 over the weekend and "a couple overnight," Dr Snee told what was expected to be the last of the daily media conferences since the outbreak.

Both Dr Snee and Hastings Mayor Lawrence Yule talked of the move to the recovery phase, Mr Yule saying that widespread investigations continue to find the cause of the contamination.

"There is no suggestion at this stage as to how this happened or who is responsible," Mr Yule said.

The 523 treated for the illness include 168 confirmed with campylobacter and 355 "probables," each taking up to five days to be confirmed. There were seven remaining in hospital today.