Cardrona's contaminated water supply led to norovirus outbreak
An acute norovirus outbreak in the Cardrona township during last year's ski season was caused by sewage contamination of drinking water and the wider environment, a peer-reviewed investigation says.
The month-long outbreak of norovirus that caused at least 53 cases of diarrhoea, vomiting and nausea was only the third documented waterborne transmission in New Zealand.
Crucially, the report also says a strategy is "urgently required" to decrease environmental contamination of drinking water supplies, improve sewage disposal and manage drinking water.
The report, in the New Zealand Medical Association journal by Dr Derek Bell, Susan Jack and Joanne Hewitt, discusses the investigation of the waterborne gastroenteritis outbreak that infected at least 53 people in and around Cardrona in mid-August and early September last year.
The Southern District Health Board yesterday confirmed the article, which mentions a hotel and resort in "southern New Zealand", referenced the Cardrona township, the hotel and accommodation providers in the village.
Cardrona Hotel, under new management earlier this year, has a supply from a bore and the hotel water system supplies water to neighbouring properties via 11 water access points. Another township accommodation provider, Benbrae, has an independent water supply and sewage system.
Public Health South investigated, interviewing 66 people, collecting samples, visiting the site, inspecting premises and water supplies.
The illness lasted, on average, for 36 hours and the cases included 12 Cardrona residents.
Hotel drinking water samples and the hotel bore were positive for norovirus, a drinking tap from the neighbouring accommodation was positive, and river samples and water downstream of the wastewater disposal field were positive.
A supply runs from a 14-metre deep bore, the water is chlorinated and pumped to holding tanks, then gravity-fed to the hotel and other access points. There was inadequate chlorination, an ineffective chlorine pump and there was surface flooding contamination, the article says.
The report's authors believed there was a link between the contamination of drinking water and illness, and that problems with the hotel water system management and wastewater, specifically groundwater intake separation distance, contributed to the outbreak. "Human faecal contamination of the bore water with norovirus is the likely cause of this outbreak."
Water management for the neighbouring resort was inadequate, unfiltered and untreated from a bore that was not fully protected, the article says.
However, the report said the approach to small community drinking supplies was fragmented and responsibilities between private owners, local authorities and regional councils were unclear.
"The current approach to rural subdivision by local government, under the Resource Management Act, can result in piecemeal private development which, in this case, has permitted drinking water sources and wastewater disposal to co-exist in close proximity to each other."
The report concluded: "A strategy to decrease environmental contamination of drinking water supplies in this busy tourist location through improved management of sewage disposal and drinking water is urgently required.
"All local government should take note of this outbreak and consider mitigating risks through a comprehensive adherence to recommended separation distances between drinking water sources and sewerage disposal systems."
Public Health South is continuing to work with the Cardrona community, Queenstown Lakes District Council and the Otago Regional Council.
Benbrae director Peter Turner said the resort's water supply was tested every three weeks and since the outbreak last year the supply had a clean bill of health and ultraviolet light treatment had also been installed.
"At the end of day the norovirus with people skiing is easily transferred," he said. Comment is expected today from other parties and local authorities.
THE OUTBREAK DETAILS
August 27, 2012: Public Health South notified; 11 people taken ill.
August/September 2012: Reports of three groups taken ill after staying at hotel, township accommodation or drinking tap water.
September 6: Inspection of hotel; kitchen has strict cleaning schedules, meticulous food preparation.
September: Water samples taken from hotel, bore, outside taps, neighbouring resort and river.
Norovirus: Globally, most cases caused by inadequately treated human wastewater.
The Southland Times