The Centers for Disease Control and Prevention is calling on doctors to more aggressively screen pregnant women for the Zika virus and to take advantage of new testing technology to improve the diagnosis, follow-up and monitoring of those who have been infected.
The guidance, published Monday, comes amid growing concerns about Zika, which is spread by mosquito bite and sexually transmitted. If contracted by pregnant women, it can result in severe birth defects — including microcephaly, which stunts children’s brain development. It has also been implicated in miscarriages and diseases like Guillain-Barre, a neurological disorder that causes temporary paralysis.
By urging testing for more pregnant women, the recommendations “will improve our ability to give definitive diagnoses of the Zika infection to those women who are at the highest risk,” said Margaret Honein, who chairs the CDC’s birth defects branch. She was also a co-author on the guidance.
Previously, Zika testing was only recommended for pregnant women if they or their sexual partner had traveled to an area where the virus was actively spreading, and if they showed symptoms. That’s changed — even if a pregnant woman or her partner doesn’t show symptoms, the CDC now says she needs to be tested.
“They’re incorporating the fact that we know transmission can occur, even in the absence of symptoms,” said Neil Silverman, a clinical professor of obstetrics and gynecology at UCLA’s medical school, and an expert in obstetric infectious diseases.
Zika has been spreading in many Latin American and South American countries, along with Puerto Rico. Public health experts warn it could reach the continental United States by summer’s end. In Florida, epidemiologists are investigating two cases in which local mosquitoes may have transmitted the virus. About one-fifth of those infected show symptoms, which can resemble the flu.
Another key part of the guidelines emphasizes the need for physicians to use various testing methods.
For instance, both symptomatic and asymptomatic pregnant women should be screened within two weeks of the date of possible Zika exposure through a DNA-based test known as PCR. PCR has been in use already, but until recently, was believed to only work within one week of exposure.
“Dominicans, Puerto Ricans and Guyanese do not have a higher risk of transmission for Zika infection,” the department said in a statement. “The data we have released simply reflects New York City’s demographics and travel patterns.”
If the PCR test turns up negative or an at-risk pregnant woman missed that initial two-week window, the CDC calls for screening with a test that searches for antibodies the virus produces. That test, which is effective for as long as 12 weeks after exposure, is considered a less reliable indicator and has drawn some criticism because it can generate false positives.
That’s part of the reason, Honein said, the CDC has emphasized the PCR approach. “We’re trying to increase the number of women who know for sure it’s a Zika virus infection,” she said.
And that could make a difference.
“The expansion of the time frame for testing of pregnant women to 14 days is quite significant — it means we can offer testing to more women and I suspect we will find more cases that would have otherwise been missed,” said Ranit Mishori, a professor of family medicine and director of global health initiatives at the Georgetown University Medical Center.
But these testing guidelines are complicated. For instance, not all physicians understand the absolute nature of two-week window. If physicians test too late, Silverman said, and the test comes up negative, patients can be lulled into a false sense of security. “This is a fast-moving target,” he said.
The CDC has been working with a number of physicians groups to help educate doctors about when and how to use different tests, Honein said.
Beyond testing, the guidance says all pregnant women in the United States and its territories should be “assessed for possible Zika virus exposure” whenever they get a prenatal care visit. That doesn’t necessarily mean testing, especially if a patient hasn’t been exposed to the virus. But it’s a firmer line than the government’s previously taken.
“This is the first time [screening] has been this strongly emphasized,” Silverman said.
There’s no known cure for Zika. If pregnant women test positive for the virus, the CDC recommends regular ultrasounds to gauge the fetus’ health and the level of risk the individual patient might face. Those recommendations are similar to the agency earlier directions.
Meanwhile, the Zika threat isn’t a new one. Lawmakers and public health advocates have been articulating concern since spring — experts argue that the summer weather is prime time mosquitoes carrying the virus to emerge in the U.S.
And figuring out the best strategy will take time. New research highlights where public health interventions need to be stronger. But these guidelines, Silverman said, track well with what’s currently known about the disease.
“The gaps become apparent as we learn more,” he said. “These are very appropriate guidelines based on our current level of knowledge … [but] that may change as we learn more.”