“But we won’t know whether it’s the mild or the aggressive variant of the H5 until later on Friday,” said the institute’s Lennart Melin.
The Institute said that it would confirm by the evening whether the birds had the highly pathogenic form of the H5 virus.
If the tests are positive, the samples will be sent for further analysis at the EU reference laboratory in Britain for final confirmation that the birds were carrying H5N1.
The birds being tested were herons, tufted ducks and other ducks.
Search efforts for additionally infected birds in the Oskarshamn area will be reduced on Friday and police check points will be taken away.
Supervised areas around the nuclear power plant outside of Oskarshamn will keep all restrictions regarding transport of fowl and poultry products.
On Tuesday, the aggressive bird virus was found in two dead tufted ducks in waters outside the nuclear power plant in Oskarshamn.
Swedish health officials decided yesterday to classify the virus as constituting a public danger.
As such, doctors who discover the virus in patients must now report findings to the Swedish Institute for Infectious Disease Control.
Doctors who treat possibly infected patients are still responsible for containing the virus, and informing all who could have come into contact with the disease.
Doctors are also responsible for information on how to prevent further spreading of the virus.
In addition to the H5N1 virus, around 25 other diseases are classified in Sweden as constituting a public danger, including the diphtheria, hepatitis A-E, cholera, anthrax, rabies and tuberculosis.