Havelock gastro disaster: New research

DNA sequencing of Havelock North outbreak suggests far greater numbers

We always knew

there were a significant number of illnesses among

people from Hastings and the wider Hawke’s Bay.

ESR scientist Dr Brent Gilpin

Havelock North’s disastrous gastro outbreak could have infected thousands more than first thought, a major new DNA analysis has found.

The researchers behind the justpublished study say a “multi-barrier” strategy around drinking water is needed to stop the catastrophe happening again — with one expert drawing a parallel to today’s Covid19 crisis.

At the time of the August 2016 outbreak, more than 5000 people were reported to have fallen ill, including more than 40 who were hospitalised, and at least four who died partly as a result.

The outbreak cost about $21m — around half of which was borne by local households, who each lost an estimated $2440 from time off work and buying bottled water — and prompted public protests and a lengthy Government inquiry.

Its cause was eventually traced to heavy rain that sent water contaminated with sheep dung into a pond, before it entered an aquifer used in the Hawke’ Bay town’s water supply.

Now scientists have revealed the true scale of the disaster — finding that campylobacteriosis case numbers could have been as high as 8320, with potentially more than 2000 of these living outside Havelock North.

ESR scientist Dr Brent Gilpin, who worked with a team from Hawke’s Bay District Health Board, the Eastern Institute of Technology and Otago and Massey universities, said fuller picture was created using whole genome sequencing to link cases.

“New Zealand has been reporting around 5500 cases from this outbreak for some time but that was based upon a telephone survey of people living in Havelock North so didn’t include any cases from the surrounding areas,” Gilpin said.

“We always knew there were a significant number of illnesses among people from Hastings and the wider Hawke’s Bay.”

Genome sequencing — effectively decoding an organism’s full genetic make-up, so it could be inspected — allowed the team to confirm that cases from outside Havelock North were really part of the outbreak, and not the result of some other cause.

The researchers estimated that between 6260 and 8320 cases of illness — including up to 2230 who lived outside the reticulation area — were linked to the contaminated water supply.

Of these, 953 cases reported by doctors, 42 were hospitalised, three developed Guillain-Barre´ syndrome — a rare disorder in which the body’s immune system attacks the nerves — and campylobacter infections contributed to at least four deaths.

An unknown number of people continue to suffer health complications.

Of the 12 genotypes the researchers observed in cases, four were also observed in water, three were also observed in sheep and one was also observed in both water and sheep.

Study co-author Professor Michael Baker, of Otago University, said he wasn’t surprised the number of infected was higher than first thought.

“You have to remember that quite a few people with this illness don’t present with symptoms,” he said.

“Generally, only about one in 10 cases of campylobacter actually become identified and notified. But this outbreak was different because there was so much awareness of it.”

Gilpin said the approach used in the study could be applied to much smaller outbreaks.

“This is a similar approach to that being used to sequence viral genomes from positive Covid-19 cases where the sequencing helps define who is part of each outbreak,” he said. “This study reinforces the importance of nationwide approach to safe drinking water. The decisions made in Havelock North regarding drinking water don’t just affect that town, but clearly have impacts far beyond.”

The Government has already taken a raft of actions, including setting up an independent national regulator of drinking water and investing more than $760m to help councils upgrade run down water services.