Explainer - Cases of cryptosporidium in Queenstown are rising and boil water notices have been issued for the town and nearby Frankton.
As of Thursday evening, 21 cases have been confirmed, but more could well be in the pipeline.
Illnesses in the area began to be reported on social media from early September, but cryptosporidium was only identified as the cause on Monday.
Te Whatu Ora / Health New Zealand is asking people who have been in Queenstown in the past 13 days experiencing a gastric upset to inform their GP.
But what is cryptosporidium, how seriously can it affect a person, and what can people do to keep themselves safe?
RNZ is here to clear it all up.
What is cryptosporidium?
Cryptosporidium is a tiny parasitic type of protozoa.
The parasite can infect people through water contaminated with human or animal faeces or by touching your mouth with contaminated hands.
People or animals who have cryptosporidium can pass on the parasites in their poo
The parasites can contaminate soil, food or water, or surfaces.
Cryptosporidium can live in the environment for long periods, especially in lakes, rivers, streams and roof water.
University of Otago parasitologist Bruce Russell said cryptosporidium could remain infectious after chlorine treatment of water supplies, but boiling killed it.
"They're got hard little shells that even resist our stomach acid, so they're very tough little customers.
"They need special treatment - usually UV and some sort of filtration," Russell said.
The latest outbreak was not unexpected, he said.
"This preventable disease is one of the most important (yet neglected) causes of gastro in New Zealand.
"We get around 500 to 1000 cases every year.
"The highest rates of cryptosporidium are seen in South Canterbury, Southern, Taranaki and Waikato DHBs," Russell said.
Massey University laboratory technician Anthony Pita said it could also be passed from person to person through the "fecal-oral route".
While boiling water would reduce the risks, household transmission of the disease was still possible, Pita said.
"The largest Cryptosporidium outbreak was recorded in Milwaukee in 1993 where an estimated 400,000 people were infected," he said.
How harmful is it?
Some people fall seriously ill with cryptosporidium and it can be life-threatening.
Babies, children and the elderly are particularly at risk from the illness.
About 10 percent needed hospital care, said Russell.
Symptoms of sickness caused by cryptosporidium can include foul-smelling or watery diarrhoea, nausea and vomiting, cramps or pain, bloating, headache, lack of appetite, a light fever, tiredness or flatulence.
Anyone suffering these symptoms should go to their doctor for testing. While there are no medicines available for cryptosporidum, the Public Health Service is notified of cases.
Russell said no vaccines for the bug exist.
"We use supportive care, or IV fluids in severe cases," he said.
After a person is infected, symptoms can take between one and 12 days to show up.
Anyone with those symptoms should contact a doctor and not go to work or school, the government's HealthEd website said.
Outbreak in Queenstown
Officials in Queenstown are working to find the source of the cryptosporidium outbreak .
Seventeen cases of infection from the parasite have been confirmed, but others who have suffered with stomach upsets have not been to a doctor.
While the water supply is not clearly linked to the outbreak at this stage, a boil water notice was issued by Queenstown Lakes District Council on 18 September.
The boil water notice applies to all residents using the town water supply in Frankton, Quail Rise, Tucker Beach Rd, Kelvin Heights and Hanley's Farm.
Jack's Point is not affected because it is on a private supply.
Council infrastructure manager Tony Avery said the council first became aware of people feeling unwell through social media comments in early September.
The council started doing extra sampling of its water supplies from 8 September, he said. However, these did not include tests for cryptosporidium.
The council's two water treatment plants take water from Lake Wakatipu to supply drinking water to about 44,708 people.
National water regulator Taumata Arowai has served a compliance order on the council for its Two Mile water treatment plant, which does not have a protozoa barrier to stop cryptosporidium entering the water supply.
This treatment plant supplies water to the Fernhill area.
The area's other treatment plant, Kelvin Heights, had a protozoa barrier, but there were doubts it was working, the regulator said.
Once it is satisfied it was operating, the boil water notice for that plant can be lifted.
"The source of the outbreak is still unconfirmed, but on the information available at the moment there is a material risk as it relates to drinking water," Taumata Arowai regulatory head Steve Taylor said.
Queenstown residents could have to boil their water for months, until the treatment plants are upgraded with barriers against cryptosporidium, Mayor Glyn Lewers said.
Taylor said the council needed to get on with its plans to improve the safety of the water supply quickly, he said.
New regulations requiring protozoa barriers came into effect in November 2022.
"Those rules had a very clear requirement that water supplies like Queenstown Lakes District Council need to have a protozoa barrier so the fact one isn't in place is of significant concern to us," Taylor said.
Several other water treatment facilities around the country do not have protozoa barriers and compliance action could also be taken against them.
Avery said public health officials were investigating possible links between the 17 cases, but so far none had been found.
"It's a bit like the early days of Covid, where if you came down with Covid, you were questioned about where you've been, what you've eaten, who you had been with.
"Talking to public health yesterday, there are no obvious links they've been able to find so far between the (cases)," he said.
Queenstown Lakes District Council (QLDC) said on Thursday evening it had "complied with the first milestone of the compliance order by delivering a community engagement plan".
A business response group also met, and its role was to review current information and inform the business community, the QLDC said.
A theory about the cause
Parasitologist Bruce Russell said his hunch was the source of the bug was livestock waste.
There were often spikes in cryptosporidium cases throughout the country at lambing time, he said.
"Infected animal waste is getting into water supplies and if you don't have a protozoa barrier there is a risk that water consumers can drink the infected spores."
Protozoa barriers and UV treatment equipment were expensive but it was unacceptable that the country had "developing world problems" with its water source, Russell said.
"Clean drinking water is what should be one of the priorities of any developed and civilised society."
Queenstown hospitality businesses are scrambling to find ways to remain open without using tap water due to the cryptosporidium outbreak.
How to stay safe
Residents and businesses should boil their water for at least a minute before using it for drinking or food preparation - including for baby formula. Boiled water also needs to be used for dishwashing, brushing teeth and for pets.
The Ministry of Health recommends washing hands thoroughly with soap and hot water, particularly before preparing food and after using a toilet, touching animals, or gardening.
Anyone with cryptosporidium should avoid preparing food for others, where possible.
It's important to clean objects that may have been contaminated, such as bathroom surfaces, door handles and toys.
Water woes in recent years
Town water supplies have come under increasing scrutiny in recent years.
An outbreak of campylobacter in Havelock North infected about 8000 people, with four associated deaths and others left with long-term disabilities, and in 2021 there were revelations of high levels of lead contamination in some Otago water supplies.
In July, it was revealed that three-quarters of the country's water supplies still did not have safety plans identifying potential hazards to water sources.
Parasitologist Russell said his lab had been trying since 2018 to get funding to tackle such problems, without much success.
"Our lab will close at the end of this year. We are the only lab in the southern hemisphere which can screen drugs targeting cryptosporidium, and only one of three in the world that can do this," Russell said.
Details about cryptosporidium and symptoms can be found on the government's HealthEd website.
