Canada's blood bank is now doing more sensitive testing for West Nile virus in Toronto and Winnipeg after the two areas recorded probable human cases of the disease.
Blood collected in both areas is now undergoing a more sensitive form of screening known as single-unit testing, the Canadian Blood Services said in a release Tuesday.
"Canadian Blood Services is working closely with public health officials so that we can identify emerging high-risk areas and respond rapidly to protect blood recipients from West Nile virus," said Dr. Graham Sher, the agency's chief executive officer.
"We continue to test every unit of donated blood for West Nile virus," Sher said. "As an added precaution, we are applying more sensitive single-unit testing in higher-risk areas to further protect people receiving blood this summer and fall."
Toronto health officials reported Monday the first probable human case of West Nile virus, a 50-year-old woman who is recovering at home. At least two other probable human cases of West Nile have been reported in Ontario this year, both in Windsor. Other probable cases have been documented in Saskatchewan, Manitoba and Quebec.
The blood services agency routinely tests every unit of donated blood across the country for West Nile virus, which is spread to humans through mosquito bites. This screening is done using a method called mini-pool testing, the standard method used by North American blood operators.
But since Aug. 2, blood collected in areas considered to be at highest risk have been undergoing single-unit testing, which is believed to be better able to detect low levels of virus.
Currently, all blood donated in areas reporting human West Nile virus activity Toronto, Windsor-Essex County, Winnipeg Health Region and Southern Saskatchewan is being subjected to single-unit testing. Blood collected at a range of clinics outside these areas in Ontario, Manitoba, Saskatchewan and Alberta is also undergoing single-unit testing.
So far this year, no West Nile virus has been detected in blood donations; last year 14 donations were found to be infected.
"The risk from West Nile virus to patients is low compared to the risk of blood shortages if people stop donating because they have been bitten by mosquitoes," said Dr. Sher. "Please take appropriate precautions against mosquito bites. And remember, most mosquitoes don't carry West Nile virus and every unit of donated blood is tested for the virus."
Canadian Blood Services is a national, not-for-profit charitable organization that manages the blood supply in all provinces and territories outside of Quebec.