The number of people infected in the Havelock North campylobacter crisis in 2016 was much higher than previously estimated, new research suggests.
Thousands of people were infected by drinking water from contaminated bores. Four people died and others were left permanently disabled.
A joint study using gene-sequencing helped scientists discover the true scale of the outbreak.
The study suggests the campylobacteriosis case number could be as high as 8320, with up to 2230 of these living outside of Havelock North.
The Institute of Environmental Science and Research (ESR) science leader Dr Brent Gilpin said the study used DNA sequencing to link cases.