By Susy Solis, CBS 11 News

BEDFORD (CBSDFW.COM) – Had some North Texans not donated blood, they might have never known they were infected with the West Nile Virus.

Each pint of blood donated to Carter Blood Care is tested for West Nile Virus and other infectious diseases, such as HIV, Hepatitis B and C, syphilis and Chagas Disease.

Creative Testing Solutions tests every pint of blood donated in North Texas.  This year, the lab has seen an unusually high number of samples testing positive for the West Nile Virus, according to Morris Dixon, Director of Operations at Creating Testing Solutions.

“The number of positive samples in the Dallas/Fort Worth area this year will more than we’ve had in total for the last 9 years,” he said. “Last year we did not have a positive donor in the testing system. This year we are well over 40 samples.”

Positive blood samples change color. When that happens the lab notifies Carter Blood Care, who then notifies the donor.

Many times, the donor had no idea they were infected.

“There are some healthy people out there that wouldn’t know normally and it just so happens they donated blood,” said Dr. Laurie Sutor M.D., the Vice President of Medical and Technical Services.

Sutor said up to 80% infected with the virus show no symptoms.

“Over the years we have found a positive donor in the testing system and notified the blood donor before the donor is actually very ill at all,” Dixon said.

Infected blood is thrown out.

“It hasn’t really affected our blood supply though. The testing that we do removes any kind of affected units from the blood supply so there is no danger to the blood supply,” Dr. Sutor said.

The good news is the blood supply has remains steady, but August is a notoriously slow month for donations.

“The heat keeps people away so we want to encourage people to donate,” Dr. Sutor said.