However, Public Health South medical officer of health Dr Derek Bell yesterday said in a press release that measures, including a "boil-water policy", had arrested the outbreak.
Dr Bell said norovirus was believed to be spread through person-to-person contact and through contaminated food and water.
"Environmental sampling to identify the source of the contamination has shown the norovirus is likely to have come from wastewater systems in the area."
Dr Bell said Public Health South would work with the Cardrona community, Queenstown Lakes District Council and Otago Regional Council to further investigate the causes of contamination and implement longer-term improvements to the wastewater and drinking water schemes.
Asked why there had been no previous public announcement about the outbreak more than three weeks ago, Southern District Health Board communications officer Stacy Belser said notices had been placed throughout Cardrona.
Queenstown Lakes District Council communications manager Meaghan Miller said the council had been assisting Public Health South, but because the water supply for Cardrona was privately owned rather than council-owned, responsibility for informing the public lay with Public Health South.
Acute gastroenteritis, such as is caused by norovirus, is classed as a notifiable infectious disease that must be reported to the medical officer of health and local authority "where there is a suspected common source" but it is unclear what responsibility the medical officer of health has to inform the public.
The Cardrona township is a popular tourist stop on the route between Queenstown and Wanaka, especially during winter, as it is close to three popular skifields.
Dr Bell said visitors "do not need to be concerned as the [Cardrona] water is safe to drink if it is boiled.""No actions need to be taken by visitors other than ensuring water from the tap is boiled before drinking it, washing teeth or washing vegetables/fruit that are to be eaten raw.
"Person-to-person transmission is the commonest way to pick up norovirus. Unfortunately, there are frequent community outbreaks ... especially [at] this time of year."
Cardrona relies on private septic tank systems and three communal wastewater treatment plants at present. However, the council is consulting over a new community scheme.
If there is sufficient support, a ratepayer-only vote will be held by the end of November.
Project manager Rob Darby has told the Otago Daily Times a community scheme would initially be privately owned, constructed and operated by a developer, but endorsed by the council and the community.
