Health officials have still not found the source of a gastro illness in Queenstown and say there is no clear pattern to food or water.

There have been 15 confirmed cases of cryptosporidium in the tourist town.

A boil water notice is in place, although there has been no confirmed link with the public water supply.

Te Whatu Ora Southern medical officer of health Dr Michael Butchard told Morning Report the number of cases in this outbreak was "very unusual".

"Cryptosporidium, the disease ... we always do expect an uptick in spring but that's because there's a strong correlation with farm animals.

"What is different about these cases is that they're all from urban settings and there's no clear link or contact with farm animals so yes, that is very unusual and that's why we're taking this very seriously."

Health officials had been in contact with 14 out of the 15 cases so far, asking a standard set of questions which included their contact with water, Butchard said.

"At this stage the source is still not confirmed, there's no clear pattern," he said.

While there was no confirmed link to water, Butchard said a boil water notice was a good step in mitigating any potential spread.

"If everyone does keep to that, then that will keep people safe.

"If it is the water, we wouldn't expect to see further cases after ... the incubation period is averaging seven days and it can be up to about 12 days, so we would expect to see cases taper off."

He urged people to also wash hands thoroughly instead of using hand sanitiser, which he said was not effective against cryptosporidium.

"For some diseases you need to use good old-fashioned soap and water and good hand-drying as well," he said.

Hospitality businesses taking boil water notice seriously

Meanwhile, a Queenstown restaurant said businesses are taking a precautionary boil water notice seriously.

Damian Brown, owner of Pedro's By The Lake Restaurant, told First Up it had been taking his staff five hours to boil the water needed for service and allowing it to cool.

'I hope this is only going to be a few days' - Damian Brown

"We had to buy a lot of bottled water and we are boiling as much water as we can," he said.

They needed it for handwashing, washing dishes, washing vegetables, using it for ice and to drink.

Brown said a nearby cafe had stopped serving iced drinks because they did not have enough water to freeze.

"I hope this is only going to be a few days ... but we're all in the same boat here, in the hospitality industry," he said.