Twenty Canadians, including a pregnant woman, have tested positive for the Zika virus, Canada's chief public health officer told a Commons committee Monday. 

"We are aware of one [pregnant woman] in Canada at this time. There may be more but we're not aware of that," Dr. Gregory Taylor, told the standing committee on health.

Taylor would not identify where the pregnant woman is from, in order to protect her privacy.

All 20 contracted the virus while visiting countries with outbreaks. There are no known instances of Canadians being infected while in Canada. 

The Zika virus is thought to cause microcephaly in newborns, which is an abnormal head size associated with incomplete brain development. 

The Public Health Agency has told women to wait two months before getting pregnant after visiting Zika-affected countries.   

Approximately three million Canadians are expected to travel to Zika-affected countries in 2016, and Taylor says the number of infected people is expected to increase. However, he tells Canadians not to worry. 

"Most of them have either no symptoms or very, very mild," Taylor said.

Blood security

The CEO of Canadian Blood Services told the committee that the virus can be transmitted through blood products, and the agency can't screen for it. 

"There is no licensed screening test that we can put in the blood system today for Zika virus. Unlike tests that we have for West Nile and HIV and hepatitis B and hepatitis C, there is no screening test we can routinely do on blood donors," Graham Sher said. 

Sher says the agency took rapid measures to protect the blood supply. Anyone who has travelled to a country with Zika must wait 21 days after returning to Canada before donating blood.

Sher says, "The risk of a unit of blood being infected by the Zika virus and entering the blood supply in Canada with our 21-day deferral policy in place is 1 in 38 million."