Swedish authorities said on Wednesday that tests had confirmed that two wild ducks found on its east coast carried the H5N1 strain of bird flu.

Preliminary tests late last month showed that two wild ducks found near the Baltic port city of Oskarshamn carried the aggressive H5 virus, but more tests were needed to ascertain that they were cases of the deadly H5N1 strain.

“The laboratory in Weybridge has now confirmed that it is an H5N1 virus, just as we thought,” the National Veterinary Institute said in a statement.

Since the first two cases were found, around a dozen wild birds found along Sweden’s southeast coast and on the Baltic island of Gotland have been identified as carrying the H5 virus.

No cases have been reported in domestic fowl.