Human faeces likely cause of Queenstown cryptosporidium outbreak

Friday, 6 October 2023

Investigations into the cryptosporidium outbreak in Queenstown suggest the most likely source is human faecal contamination of the water supply.

In a statement on Friday, Te Whatu Ora – Health New Zealand medical officer of health Dr Michael Butchard said based on the information to date, the most likely hypothesis was the outbreak started through human faecal contamination of the source water in Lake Wakatipu.

This water was collected into the Two-Mile water treatment plant’s intake pipes and then got into the water reservoir.

“From there, it has then been distributed around the Two-Mile water distribution network to homes and businesses, most likely over a number of days.

“While the results are unable to tell us exactly where the contamination came from, genotyping shows that the outbreak cases are all linked since they are all of the same hominis genotype, which is also evidence of a human rather than an animal source.

Butchard said there could be several possible contamination sources “as only a very small amount of faecal contamination – for example from just one person – is enough to cause an outbreak of crypto”.

“Possible sources could have included sewage dispersal from watercraft near the Two-Mile Lake Wakatipu drinking water intake, contamination from swimmers or other lake users, wastewater overflows or other undetected faults in the wastewater system. But we are unlikely to ever know.”

As of 10am Friday, there have been 62 confirmed cases of cryptosporidium (crypto) and 18 probable cases. Twenty-four cases are under investigation.

The lates news means a boil water notice will remain in place as the Queenstown Lakes District Council (QLDC) works to put install protozoa barriers at its Two-Mile water treatment plant, following directions from drinking water regulator Taumata Arowai.

This follows Thursday’s news that the boil water notice for the Kelvin Heights water distribution zone, which supplies water into Frankton, had been lifted.

Butchard said while water testing had not shown any positive results for cryptosporidium, testing itself was complex and not always conclusive, meaning negative crypto results from water testing could not rule out water contamination being the source.

Investigations had not flagged any food, beverage, event, or location as a source of the outbreak either – leading authorities to conclude water contamination was the likely cause.

This was further supported by the fact that the boil water notice put in place on September 18 had effectively halted the continuous source of contamination.

“We know the boil water notice in particular, along with other public health measures, has been very effective in halting the spread of crypto, and we thank everyone across the community who has played their part in following the advice to help limit the spread.

“However, crypto is still very much present in the community, with a high risk of re-infection and person-to-person spread. This means the risk of further spread of crypto is still very real, and higher than before the outbreak began.”

This was why Butchard fully supported the direction from Taumata Arowai and QLDC that the boil water notice remained in place for the Two-Mile Water Treatment Plant distribution zone, until the protozoa barrier was put in place.

“In the meantime, we continue to strongly encourage the community to boil water, wash and dry hands thoroughly and take care to avoid swimming pools and facilities where crypto could be spread.”

Taumata Arowai head of regulatory Steve Taylor said the compliance order served on the council required it to advise consumers to boil water until a protozoa barrier was in place at the Two-Mile water treatment plant.

“Protozoa and other waterborne microorganisms can present a serious risk to public health. That’s why a multi-barrier water treatment system is required. The Queenstown supply at the Two-Mile water treatment plant is currently operated without a protozoa barrier.

“We are working with QLDC to ensure a cost-effective and pragmatic source water testing plan continues,” he said.