Cattle and other four-legged farm animals may be behind the gastro outbreak that has made thousands sick and may have contributed to an elderly woman's death.
Poultry manure may now be out of the frame.
An interim scientific analysis indicates contamination from cattle, sheep and deer may have been present in Havelock North's water supply, which in normal times is not disinfected with chlorine.
It is estimated that more than 4000 people in the Hawke's Bay town have suffered symptoms such as vomiting, diarrhoea, headaches, muscle pain and fever from drinking the town's water when it was contaminated with campylobacter bacteria.
Hawke's Bay medical officer of health Dr Nick Jones said animal faeces might have caused the contamination.
And now interim test results from the Institute of Environmental Science and Research, published by the Hastings District Council, may back this view.
The testing "suggests the isolates from reticulated water, from clinical cases linked to this water or in a cluster suggesting a common source, are consistent with ruminant source such as cattle, sheep or deer," the ESR report says.
"These genotypes are not consistent with a poultry source. Isolates from the bore sample are most closely related to wildfowl isolates."
ESR said its tests linked a large number of the sick people from the Havelock North outbreak with campylobacter jejuni strains found in the water. Many different strains were present.
Initial high level genetic analysis suggested the campylobacter bacteria were more likely from ruminant animals. Some strains in the water supply were of kinds likely to be from wildfowl. Rivers would often carry campylobacter from both ruminant and wildfowl sources.
Authorities advise to boil water in Havelock North and have been chlorinating the supply.
Medical testing this week confirmed that 89-year-old Jean Sparksman, who had been living at the Mary Doyle village in Havelock North, contracted campylobacter before she died last Saturday. She also had other significant health problems. Her death, including any role of campylobacter, will be investigated by a coroner.
Hastings mayor Lawrence Yule has said he will speak to Mrs Sparksman's family. He wanted "to in some ways apologise that the situation has ended up like this, but what I say will depend on what the coroner has found", RNZ reported.
Hawke's Bay Hospital has had a peak of around 20 people with gastric illness admitted this week and two in intensive care.