ATLANTA - There has been a dramatic jump in the number of pregnant women in the U.S. infected with the Zika virus.
The CDC says 279 women have been exposed to the virus, 157 here in the mainland US, the rest in Puerto Rico and other U.S. territories. Many of the 279 pregnant women being monitored by the CDC are still pregnant and so the outcomes of their infection aren't clear at this time.
The major spike comes as the Atlanta-based health agency changes the way it monitors pregnant women exposed to the mosquito-borne virus.
The CDC says protecting pregnant women and their unborn babies is the number one priority of its Zika response plan.
That's why the agency is increasing its monitoring to include not just pregnant women with lab-confirmed Zika virus who have symptoms, but Zika-positive pregnant women with no symptoms.
So, why the change?
Recent case studies show even when a Zika-infected pregnant woman has no obvious symptoms, she can still have pregnancy complications.
At the CDC Headquarters in Atlanta, hundreds of staffers inside the agency's Zika Response Plan emergency operations center are tracking an outbreak that seems to be one step ahead of everyone.
Dr. Denise Jamieson is co-lead of the CDC's Zika Plan Pregnancy and Birth Defects Team.
“I mean I've been at the CDC for 20 years, and I've never been involved with something that evolved so quickly,” says Dr. Jamieson. "We are literally learning more about this every day.”
Still, there are many unknowns, and that is why Dr. Jamieson says expanding monitoring can yield some important clues.
"We don't know how often pregnant women get infected with Zika,” she says. “We don't know how often when they get infected, their babies are infected. We know Zika is associated with microcephaly and brain abnormalities, but we don't know what other problems these babies may have."
Zika virus is primarily spread by infected mosquitoes. But never before has one virus caused such severe birth defects and pregnancy complications. And with summer and mosquito season coming, Dr. Jamieson is urging Americans to take steps to avoid getting bitten by mosquitoes.
"There are a whole lot of really good reasons to avoid mosquito bites, whether you are pregnant or not,” Dr. Jamieson says