Zika virus infection during pregnancy may increase birth defect risk 20-fold, CDC study finds

— -- The Zika virus may increase the risk that a pregnant woman has a child with certain birth defects by up to 20-fold, according to a new study.

Researchers looked at data on infants both before the spread of the Zika virus and after to understand the risk of the virus on a developing fetus, according to a study published in the U.S. Centers for Disease Control and Prevention's latest issue of the Morbidity and Mortality Weekly Report.

The mosquito-borne Zika virus often causes mild symptoms in adults but has been found to cause birth defects, including microcephaly, after it spread to the Americas last year. Microcephaly is characterized by a malformed or smaller head and brain, and can result in serious developmental delays.

Common symptoms of the Zika virus include fever, rash, joint pain and conjunctivitis, according to the CDC. Approximately one in five people infected with the virus show symptoms. Severe complications from the virus that require hospitalization are rare, according to the CDC.

In order to estimate the risk to the fetus if a pregnant woman is infected with the Zika virus, the researchers analyzed data from the U.S. Zika Pregnancy Registry (USZPR) and compared it to birth defect surveillance data collected from Massachusetts, North Carolina and Georgia between 2013 to 2014.

They examined the prevalence of multiple birth defects among the infants, including microcephaly, eye abnormalities, brain malformations and central nervous system dysfunction.

The USZPR monitored births among women likely to have had Zika infection from January to September 2016. The researchers found birth defects among 26 infants and fetuses among the 442 completed pregnancies of women with possible Zika infection. From this data, the researchers estimated the rate of birth defects among infants born to women with Zika-affected pregnancies is 58.8 per 1,000 completed pregnancies.

This is a 20-fold increase from data taken prior to the spread of the Zika virus, which estimated 2.86 infants among 1,000 live births had birth defects. The study authors acknowledge the study had limitations since those on the USZPR list may have been put under added scrutiny compared to an average pregnant woman. Additionally, there may be issues with generalizing the data taken from three states to the entire U.S., the researchers noted.

Dr. William Schaffner, an infectious disease expert at Vanderbilt University Medical Center, said the study still gives important information to public health officials about the risks of being infected with Zika during pregnancy.

"We knew it was increased but we didn't know how much," Schaffner said of the increased risk of birth defects. "These studies really nail what that increase is and ...i t's huge."

As the weather starts to warm, public health officials will anxiously be watching to see if the disease returns, Schaffner said.

Public health officials have so far been heartened that the disease has not come roaring back in the Caribbean or in Central America, he said. But for those who have already had children affected by the Zika virus, the impact of that infection may follow them for decades to come.

"It's these birth complications and complications in the fetus that make it a public health problem, and now it's well-defined what the public health magnitude is," Schaffner said. "It's a lifetime of complex care for those babies."