How an Alberta, Canada swine herd became infected with the H1N1 Flu Outbreak Virus remains a mystery after officials ruled out the prime suspect.

A spokesperson for Alberta Health and Wellness says blood tests have shown that a carpenter who worked for half a day on the farm before heading home with a flu-like illness did not introduce the virus to the herd.

“We've determined it wasn't the carpenter,” says spokesperson Howard May.

May says health officials are starting to believe that they will never determine how the virus made its way into the herd, the only pigs in the world to have tested positive for the H1N1 Flu Outbreak Virus.

“Since serological (blood) tests indicated the carpenter didn't have H1N1, someone else must have brought it in, but it is unlikely we will ever be able to pinpoint exactly who,” May says.