It's the earliest West Nile Virus has ever been found in Halton.
The first batch of mosquitoes collected in the region has come back positive for the virus.
They were caught in traps in Oakville and Milton.
Dr. Bob Nosal, Halton's medical officer of health, says West Nile is not usually found until late July or August.
But he thinks the early spring changed the situation this year.
So far there have been no positive results found in Hamilton.