Health officials have published the first comprehensive view of Zika-linked birth defects occurring in the U.S.
The study is the largest so far to estimate the risk of severe birth defects from Zika infections in pregnant women, researchers report Wednesday in the Morbidity and Mortality Weekly Report,
"Although Zika may seem like last year's problem, or an issue confined to Brazil, there have been more than 1,600 cases in pregnant women reported here in the U.S.," says the acting director of the Centers for Disease Control and Prevention, Dr. Anne Schuchat.
And the cases aren't slowing down.
"We're still seeing about 30 to 40 Zika cases in pregnant women each week in the U.S.," Schuchat says. "Zika is here to stay."
Here's how the epidemic has affected babies in the U.S. so far:
- Nearly 1,300 pregnant women, in 44 states, had laboratory evidence of a Zika virus infection in 2016. About 970 of those women have completed their pregnancies.
- Of those women with laboratory evidence of Zika virus, there were 77 reported pregnancy losses and 51 babies born with birth defects, including 43 babies with microcephaly or brain abnormalities. Other babies had eye abnormalities or neural tube defects.
- The women mostly caught the virus in 14 countries or territories across Latin America and the Caribbean. A few of them picked up the infection in the Republic of Marshall Islands in the South Pacific, or Cape Verde off the coast of West Africa.
- Overall, the risk of severe birth defects was about 5 percent among women who were infected with Zika during pregnancy. That risk is comparable to what's been found in other countries.
- That risk jumped to 10 percent for mothers who's Zika infections were unambiguously confirmed. It rose even higher, to 15 percent, for those infected in the first trimester.
It may be helpful to compare these Zika statistics to those for other viruses that cause birth defects. Each year about 8,000 babies are born in the U.S. with disabilities because of infection with cytomegalovirus, or CMV.
And in general, birth defects from all causes affect more than 100,000 babies in the U.S. each year, the CDC reports.
Still, there are big gaps in our knowledge about Zika, says epidemiologist Margaret Honein, who led the study. Some of those gaps may lead to an underestimation of the problem
For starters, doctors still aren't sure about the full range of problems caused by Zika infections in utero. A baby can be born healthy, with a normal head size, but then develop neurological problems later on. Some may have seizures or muscle spasms, or a baby may have problems that are only detectable by a brain scan.
For this reason, the CDC now recommends babies infected with Zika have ultrasounds or CT scans of their brains to evaluate any abnormalities not apparent at birth. So far, Honein says only about one in four babies have had these exams.
"I want to highlight the need for care and evaluation of these infants," she says. "This brain imaging, such as a head ultrasound, is really important. We know that there can be babies who don't have microcephaly but imaging of the brain can reveal serious brain defects."
Although cases of Zika have started to decline in many parts of Latin America, Honein says, the risk is still high for pregnant women.
"So we are trying to emphasize: Pregnant women should not travel to any areas where there's a risk of Zika," she says.
Right now, Zika has been reported in most countries in Latin America, the Caribbean and Southeast Asia as well as several counties in southern Florida and southern Texas.