Two pregnant women in B.C. have tested positive for Zika virus, health officials have confirmed.

The women are being regularly monitored with special higher resolution ultrasounds at B.C. Women's Hospital, and so far no complications in their pregnancies have been reported, according to David Patrick, a medical epidemiologist at the B.C. Centre for Disease Control.

"They look at whether the baby is growing normally for the date. They take a look at the size of the baby's head in particular, and they look for other abnormalities within the baby's skull as it develops," he said.

Last week Zika virus was confirmed as a cause of the birth defect microcephaly and other serious birth defects, by the U.S. Centers for Disease Control and Prevention.

Low risk to pregnancies

But the vast majority of women infected with Zika have no complications with their pregnancies, which generally only occur when the women are quite sick from the virus during their first trimester, said Patrick.

Zika cause confirmed

Janine Santos holds her three-month-old son Shayde Henrique, who was born with microcephaly. Zika is now proven as a cause of microcephaly — or, unusually small heads — the CDC says. (Andre Penner/Associated Press)

"If women have just been exposed and had the virus pass through their body without many symptoms, the risk to the baby is actually pretty low," he said.

It is also still possible to test positive for the virus and not actually be infected, he notes.

"The testing is getting better, but it is not super-good, so you really wouldn't want to make a decision based on a false-positive test," Patrick said. "The most important message is to follow the pregnancy really closely with your doctor and an obstetrician with the right kind of ultrasounds."

7 positive cases in B.C.

Along with the two pregnant women, three other women and two other men have tested positive for the mosquito-borne virus, but none have required hospitalization, he said.

"For the most part, there is no specific treatment for Zika. It is a short-lived infection that passes through the system," he said.

Nevertheless, women who may be or could become pregnant, and their partners are warned to take special precautions to avoid infection or sexual transmission of the virus.

The infected travellers tested positive after returning from trips to Haiti, Colombia, El Salvador and Barbados, but no cases have been reported in travellers returning from Mexico, noted Patrick.

A total of 635 people have been tested in B.C. since the outbreak was first detected, but the rate of testing in B.C. has dropped from about 80 people per week to about 35 people per week, he said.

Last month Canada's chief public health officer said 20 Canadians, including a pregnant woman, had tested positive for Zika virus.