There are also another 10 probable cases and another eight under investigation.
But the source of the outbreak is yet to be identified, and a boil water notice remains in place.
Te Whatu Ora Southern Medical Officer of health Dr Susan Jack told RNZ's Checkpoint programme tonight the source could include drinking water, recreational water, food or drinks.
"We're still actively searching for the source ... so far nothing has come up as a red flag from our interviews with cases."
Authorities were now also finding person-to-person spread.
"So handwashing with soap and water is absolutely critically, and especially drying your hands before you continue, Dr Jack said.
'Unfortunately, alcohol sanitisers are not effective for crypto, and then our other big message is not to go swimming until you've had no symptoms for at least two weeks."
The illness can cause severe diarrhoea, nausea, vomiting, stomach cramps and pain, headache, lack of appetite, fever and tiredness, the government's HealthEd website said. Babies, the elderly and immune compromised are particularly vulnerable if they get infected.
Anyone with those symptoms has been asked not to go to school or work, as the parasite can be spread easily, and to contact a doctor both for advice and because public health officials are carefully monitoring the situation.
A notice to boil all water used for food, drink or dishwashing is still in place for all properties and businesses on the Queenstown water supply.
Queenstown Lakes District Council said water needs to be boiled for more than one minute. It warned that water to be made into ice, filtered water and water heated in zips all still need to be boiled for 1 minute additional to those treatments.
Dr Jack said most people who had been infected were aged between 15- and 39-years-old - which was about what they would expect as a representation of the population's demographics, and most had been in Queenstown from mid-August onwards.
"It still could be the drinking water supply, we're not ruling that out, but it's looking like it's what we called point source outbreak - so something happened, there was a contamination event, and that could have been in the water, or through food or beverage or something else.
"Our next steps is with help from ESR [ the Institute of Environmental Science and Research] we've developed a new more detailed questionnaire, so we'll be going through that with the 40 existing cases and all new cases.
"Then if there's a red flag such as a specific food or beverage or location we'll direct our efforts toward that."
A pool at Alpine Aqualand had been closed, as cryptosporidiosis infections could be caught from swimming pools - but Jack said it was able to reopen after it had been checked over: "They've looked at what they're doing for filtration, and feel that it's adequate".
Hospitality industry frustrated
The increase comes as some in the popular tourist town's hospitality industry have made their frustrations known.
The Rees Hotel chief executive Mark Rose said since the outbreak began there had been cancellation costs of "about $50,000 to $60,000".
"But the real cost is the reputation damage."
Mr Rose said the issue had become a national one.
"Queenstown is the gateway for tourism in the country."
Health advice
No one who has had symptoms of crypto (diarrhoea) should enter a swimming or spa pool, until they have been symptom free for two weeks.
This included sharing bath water with others.
The most common symptom of cryptosporidium infection is smelly, watery diarrhoea and stomach cramps.
People who live, work or have visited Queenstown and Frankton on or after August 18 and have symptoms of diarrhoea and/or stomach cramps, should call their GP or health provider to inform them and arrange testing if needed.
You can call Healthline at any time on 0800 611 116 for advice for managing your health.
- Additional reporting by ODT Online
