U.S. health officials are investigating whether four patients in the states of Georgia and Florida were infected with West Nile virus through donated organs.

The Centers for Disease Control and Prevention (CDC) says the four patients all received organs from a woman who died in a car crash in Georgia in August. So far, tests have confirmed a West Nile virus infection in one of the four patients.

All previous cases of the virus in the United States have resulted from contact with mosquitos.

This year, at least 28 people have died in the United States from West Nile virus, which can cause inflammation of the brain.