Cryptosporidiosis illness occurs as a result of infection by the cryptosporidium parasite, which spreads easily between people.
Sixty cases have been confirmed, and a boil water notice remained in place for everyone using Queenstown mains water, including to wash dishes and prepare food and drinks and to feed pets.
Medical Officer of Health Dr Susan Jack said water testing was happening throughout the drinking water distribution network but authorities were not testing specific businesses.
"No crypto has been detected from any testing so far, but further results are awaited," Jack said.
"It is important to note that crypto is very hard to detect in water, so unfortunately even a negative result cannot rule out crypto being or having been in a water supply."
In an update just after midday today Dr Jack said there were 60 confirmed cases of crypto), 15 probable cases, and 12 under investigation.
ESR, the government's environmental science agency, was completing detailed questionnaires with as many cases as possible, she said.
"The preliminary analysis should come through in the coming days and what we are looking for is if any location or food or beverage is flagged - then we would do further investigation into that. It may be that there was a contamination event into for example water or a particular food that has now passed.
"We are still seeing cases because the incubation period could be as long as 12 days. Extensive water testing is under way and will continue in the drinking water network - but again none of the tests have shown crypto to date.
"However, we may never know the source for certain."
But Dr Jack said she remained hopeful they could reach some conclusions once all the information and test results were collected.
Queenstown Lakes District Council said more details about cryptosporidiosis and its symptoms could be found on the government's HealthEd website.
Symptoms can include diarrhoea, nausea and vomiting, cramps or pain, bloating, headache, lack of appetite, a light fever, tiredness or flatulence. Anyone with those symptoms was recommended to contact a doctor and not go to work or school, because of how easily the infection could be spread, HealthED said.
