Human faeces has been identified as the most likely source of the contaminated water supply which has caused Queenstown's gastro bug outbreak.
Te Whatu Ora said investigations had concluded the cyptosporidium outbreak which has affected 62 people started through human faecal contamination of the source water in Lake Wakatipu.
But the exact source is unlikely ever be known.
A boil water notice will continue as Queenstown Lakes District Council works to put in place protozoa barriers at its Two-Mile water treatment plant, following direction from drinking water regulator, Taumata Arowai.
Medical officer of Health Dr Michael Butchard said the most likely hypothesis was the contaminated water had been collected into the Two-Mile water treatment plant’s intake pipes before collecting in the water reservoir.
"From there, it has then been distributed around the Two-Mile water distribution network to homes and businesses, most likely over a number of days.
“While the results are unable to tell us exactly where the contamination came from, genotyping shows that the outbreak cases are all linked since they are all of the same hominis genotype, which is also evidence of a human rather than an animal source.
“There could also be a number of possible contamination sources, as only a very small amount of faecal contamination – for example from just one person – is enough to cause an outbreak of crypto.
"Possible sources could have included sewage dispersal from watercraft near the Two-Mile Lake Wakatipu drinking water intake, contamination from swimmers or other lake users, wastewater overflows or other undetected faults in the wastewater system. But we are unlikely to ever know.”
Dr Butchard said while water testing had not shown any positive results for Cryptosporidium, testing not always conclusive
