Zika spawned a 10 percent birth defect rate in infected pregnant women in the U.S. last year, the government said Tuesday in a new study that shed light on the “sobering” risks of the mosquito-borne scourge.
The Centers for Disease Control and Prevention, which reported the findings, said the problem was particularly acute among women who were infected during their first trimester — a critical period for fetal brain development — and that too few women are scanning their infants for problems that can develop weeks or months after birth.
“It really reaffirms to me how serious this virus is,” acting CDC Director Anne Schuchat told The Washington Times.
The CDC looked at nearly 1,300 pregnant women who had brushes with Zika in 2016, when the virus exploded across Latin America and began to spread in Florida and Texas. Those with suspected cases of Zika had a 5 percent rate of virus-spawned birth defects, while those with lab-confirmed cases showed a 10 percent rate.
For most people, Zika doesn’t carry a big impact, and many don’t even know they’re infected. But scientists last year established a link between infections and an alarming spike in the rate of babies born with abnormally small heads, or microcephaly.
The CDC told pregnant women to avoid any area with mosquito-borne transmission if they could, or to protect themselves against mosquito bites if they had to travel to those countries.
They also warned those who had traveled to infected areas, or whose sexual partners had traveled, to use precautions to prevent the disease from spreading through sex.
Scientists said the Zika outbreak marked the first time that an insect-borne disease was tied to birth defects, and the problems weren’t limited to microcephaly.
“I think the virus in this case was just as serious we feared,” Dr. Schuchat said.
The new CDC study excluded hard-hit Puerto Rico, looking instead at Zika-related pregnancies reported in 44 states.
The women whose children had defects gave birth in the U.S., each of them were infected abroad in one of 16 countries — mainly in Latin America and the Caribbean, though the list spanned from the Marshall Islands in the Pacific Ocean to Cape Verde off the coast of northwest Africa.
The CDC reviewed 1,297 pregnancies with possible Zika infection from Jan. 15 to Dec. 27, including 972 completed pregnancies with reportable outcomes — 895 live-born infants and 77 pregnancy losses.
Birth defects were reported for 51 out of the 972 completed pregnancies. Among the subset of pregnancies in which Zika was actually confirmed, birth defects were reported in 24 out of 250 cases.
The CDC said 43 out of the 51 infants or fetuses with birth defects suffered from microcephaly or other brain abnormalities, while the rest had eye abnormalities or central nervous system problems without brain abnormalities.
The problem was especially prevalent in mothers who were infected in the first trimester, with 15 percent of completed pregnancies — nine out of 60 — in the lab-confirmed category experiencing birth defects.
The U.S. findings roughly align with published analyses of women in Rio de Janeiro and French Guiana that found a birth-defect rate of 10-13 percent among women infected in their first or second trimester.
The CDC is urging Zika-affected mothers and their doctors to do follow-up testing, after studies showed that birth defects can develop months after birth.
“This is a new condition, and clinicians are just learning how to care for these babies,” Dr. Schuchat said.
The CDC study said only a quarter of infants born to mothers with possible Zika infection received brain-imaging scans, so it is important to educate doctors about risks that can appear later on.
Understanding the outbreak itself proved elusive last year. Scientists acknowledged they were learning new things about the virus every day — for instance, they discovered the virus could be sexually transmitted.
The Obama administration released maps indicating that disease-carrying mosquitos could potentially strike as far north as New York City, as it fought with congressional Republicans over new funding to the combat the disease.
Yet by and large, the disease remained a travel-related one for the U.S.
The CDC itself said the states were unlikely to see the type of rampant transmission that hammered parts of Latin America, due to widespread use of window screens and air conditioning, plus the U.S.’s relative population density.
Ultimately, mosquito-borne transmission in the states was limited to hot spots in Florida and Texas.
The administration took the unprecedented step of warning pregnant women to avoid parts of Miami that saw the first cases of mosquito-borne transmission.
Local transmission petered out in the U.S. as colder winter temperatures set in, tamping down mosquito populations, though officials worry about a resurgence as spring and summer approach.
Florida Gov. Rick Scott, a Republican, has been holding a series of roundtable discussions in the state to discuss preparations.
The majority of people infected with Zika do not show symptoms, so some people undoubtedly acquired Zika without knowing it.
That means a segment of the population might have developed immunity to Zika during the first go-around, according to Dr. Amesh Adalja, a researcher at the Johns Hopkins Center for Health Security, who said the U.S. got a jump start on the disease by sounding the alarm early on.
Yet “complacency is always a risk when headlines fade,” he said, “so it is crucial to maintain a heightened sense of urgency.”
• Tom Howell Jr. can be reached at thowell@washingtontimes.com.
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