“I currently have no reason to think it's something else,” infectious disease control doctor Stephen Stenmark, told news agency TT.
The Cryptosporidium parasite spread through the tap water and caused a stomach flu outbreak in Östersund in 2010. It took several months until residents in the Jämtland city could drink the city's tap water again.
But despite Stenmark's statement, water tests have still not shown evidence of the Cryptosporidium in the Skellefteå water supply.
In an online web survey conducted by Skellefteå and the Swedish Institute for Communicable Disease Control (Smittskyddsinstitutet – SMI), 3,600 people say they have been affected by the stomach flu.
Stenmark said that more than half of the patients they have tested have turned out to be positive for a Cryptosporidium infection.
And an analysis shows that the group of Skellefteå residents who drink the most water, more than two glasses a day, are more sick than healthy. “The more water you drink, the greater the chances are that you'll be sick and the stronger the theory becomes that the the parasite is spreading in the water,” Stenmark told TT.
Thirty-nine patients were confirmed affected with the parasite on Friday compared to 24 such cases on Thursday.