By Brenda Goodman, MA
WebMD Health News
Reviewed by Hansa D. Bhargava, MD
Feb. 26, 2016 -- Pregnant women who recently traveled to areas where the Zika virus is being spread by mosquitoes are facing a dilemma -- whether or not to get a blood test to check for the infection.
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That's the recommendation by the CDC, even if they don't show symptoms, don't remember getting mosquito bites, and never felt ill.
Public health labs around the country are warning doctors that it may take as long as 6 weeks for patients to get results of those tests, resulting in long, anxious waits for information that may be of limited use.
Doctors, too, are resisting the CDC's advice, afraid women might terminate their pregnancies based solely on blood test results, without waiting for stronger evidence from ultrasound scans that show a fetus has actually been harmed.
A growing body of scientific evidence suggests that the Zika virus can cause a devastating birth defect called microcephaly, a condition that causes a baby to be born with an abnormally small head and brain damage. Some children born with severe cases may die soon after birth. Others who live could need a lifetime of medical care, therapy, and support services.
Ultrasound scans often don't reveal the telltale signs of microcephaly or other birth defects until after the 24th week of pregnancy, when a woman is in her third trimester. That's well after most states say it's legal to get an abortion.
"That's a problem in terms of making a decision about the pregnancy," says Alfred DeMaria, MD, who directs the public health laboratory for the Massachusetts Department of Public Health.
DeMaria says some obstetricians have told him they are discouraging patients from getting the blood test, against the CDC's guidelines.
"What the general public hears is that, 'If I had Zika, I'm going to have a baby with microcephaly,'" DeMaria says. "That's a false notion."
Yet new findings out Friday from the CDC suggest that women might be right to be worried. Of the nine confirmed Zika infections in pregnant women who had traveled to other countries and returned to the U.S., only two have resulted in apparently healthy births so far.
In the other seven cases, two resulted in miscarriages, one baby was born with microcephaly, two pregnancies are continuing without known complications, and two women elected to end their pregnancies. In one case, the pregnancy was terminated at 20 weeks after an ultrasound showed signs of severe brain damage in the fetus. The details of the other termination were not reported.
The study also offered the most detailed picture so far of risk according to the stage of pregnancy when a woman was infected. As experts had suspected, infection during the earliest stage of pregnancy, when a baby's organs are still forming, seems to be linked to the worst outcomes.
Six women were infected with Zika during the first 3 months of pregnancy, or first trimester. Two of them miscarried, two aborted their pregnancies, one baby was born with microcephaly, and one pregnancy is still ongoing and apparently healthy.
Of the two women infected during their second trimester, one baby is healthy so far and the other pregnancy is continuing. A woman infected during her third trimester delivered a healthy baby.
The CDC is investigating 10 more cases of possible Zika infection during pregnancy.
Doctors aren't yet sure how often the virus, which is still considered to be primarily mosquito-borne, may cause microcephaly or other birth defects during pregnancy. Studies are underway to try to determine the true risk to an unborn child and whether or not other factors like nutrition or perhaps getting two infections -- dengue fever and Zika are the two most commonly mentioned -- together might play a role.
DeMaria says even though Brazil is seeing many more cases of microcephaly than it normally does, it still seems to be an uncommon outcome based on the 1.3 million estimated Zika infections there.
So far, there have been over 5,000 cases of suspected microcephaly reported in Brazil. Doctors have confirmed that just 583 meet the strictest criteria for diagnosing the condition. More than 4,000 remain under investigation.
Right now, there are two ways to check for Zika. One test can pick up pieces of the virus's genetic code in people with active infections. But after the body clears the infection -- a process that takes about 2 weeks after the first symptoms appear -- that test won't work. Since 80% of people don't experience symptoms, though, many don't know when they were infected, if at all. So they aren't eligible for that test.
Fortunately, doctors can run a different test to look for proteins, called antibodies, that are made by the immune system to fight the virus.
That test can detect the antibodies in the blood up to 3 months after a person was infected. But it's not very specific. A person will test positive if they've been infected with any of a number of related viruses, including dengue and chikungunya, which are also passed by mosquitoes to people.
For now, only one laboratory in the country -- a CDC lab in Ft. Collins, CO -- can perform both the initial screening test to look for the antibodies and a specialized follow-up test to determine whether those antibodies were made in response to Zika or a related virus like dengue or chikungunya.
The follow-up test -- called a plaque reduction neutralization test, or PRNT -- requires that lab workers mix the Zika virus along with a sample of the patient's blood.
It's highly accurate, but it takes about a week to get results. And the Ft. Collins lab is getting hundreds of samples to test each day.
"We're getting more and more samples all the time. Yesterday we received somewhere between 400 to 450 samples. It's busy right now," says Ann Powers, PhD, chief of the alphavirus laboratory at the CDC's National Center for Emerging and Zoonotic Infectious Diseases.
Powers says the CDC is racing to get state laboratories across the country the tools they need to do the test closer to home, but staff will need additional training and labs will need to handle samples of live Zika virus, something that requires a certain level of security and care. Not all labs can or want to work with the virus, Powers says.
DeMaria thinks it may be up to 3 months before his lab -- one of the most sophisticated in the U.S. because it already does surveillance for arboviruses -- is ready to do the test. In the meantime, he's telling doctors in the state that it may take as long as 6 weeks to get test results back for their patients.
He says some doctors feel the long wait simply isn't worth the anxiety for patients. Other doctors agree.
"It's very, very difficult," says Jennifer E. Ballard, MD, director of the perinatal center for maternal-fetal medicine at Washington Hospital Center, in Washington, D.C. Many of the patients in Ballard's practice travel internationally for work. "It does cause our patients a fair amount of worry."
"I kind of present it as a risk-benefit to the patient before we decide to send the test," Ballard says. "I don't say no. But I definitely give them the knowledge that they may not be able to benefit during the pregnancy with that testing or that it may come back too late, but at least they might have some explanation if something does go off," she adds.
Other doctors share her caution in offering the test to all pregnant travelers.
"They may be stuck making some hard choices on the blood test," says Laura Riley, MD, director of obstetrics and gynecology infectious disease at Massachusetts General Hospital in Boston. So far in her practice, which handles about 3,600 deliveries a year, about 50 patients have met the CDC guidelines to have their blood sent for testing. She says most of her patients have wanted the test for the peace of mind a virus-free result might offer.
"The issue we have is that if you test positive [on the blood test], and your ultrasound is normal, is it really normal? That's a piece we don't know. The other thing we don't know is if you test positive and your ultrasound is normal, should we do an amniocentesis, and what are we going to do with that information?" Riley says.
Riley says amniocentesis, where a long needle is inserted into the womb to draw a sample of the fluid surrounding the fetus, might tell you whether a baby has been infected "but not whether it's been affected," she says. "That's what most women want to know, 'Is my baby OK?'"
And an amniocentesis is not without risk. It increases the risk of miscarriage and pre-term delivery, she points out.
"It's dicey," she says.
SOURCES: Alfred DeMaria, MD, Medical Director, William A. Hinton State Laboratory Institute, Bureau of Infectious Disease Prevention, Response and Services Massachusetts Department of Public Health, Jamaica Plains, MA. Tom Frieden, MD, director, U.S. Centers for Disease Control and Prevention, Atlanta. Ann Powers, PhD, chief of the alphavirus laboratory at the CDC's National Center for Emerging and Zoonotic Infectious Diseases, Ft. Collins, CO. Jennifer Ballard, MD, Director of the Perinatal Center for Maternal-Fetal Medicine, Washington Hospital Center, in Washington, D.C. Laura Riley, MD, Director of Obstetrics and Gynecology and Infectious Disease, Massachusetts General Hospital, Boston. World Health Organization, Zika Situation Report, February 26, 2016. CDC, Morbidity and Mortality Weekly Report, February 26, 2016.
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