CDC Identifies Risk of Developing Zika Complications Based on Trimester of Infection

"As these latest findings illustrate, Zika virus poses a serious threat to pregnant women and their babies, regardless of when the infection occurs during the pregnancy", CDC Acting Director Anne Schuchat said in a statement. When the infection was in the second trimester, 5% of pregnancies resulted in a birth defect, and in the third trimeter, 4% of pregnancies were affected.

The CDC did not sort the data by territory and neither Schuchat nor Peggy Honein, PhD, MPH, who co-leads the CDC task force on Zika-related pregnancy and birth defects, would say how many cases came from Puerto Rico, one of the countries hit hardest by the Zika virus epidemic.

Among the women with confirmed Zika infection during the first trimester, eight percent, or almost one in 12, had a baby or fetus with Zika virus-associated birth defects. CDC officials on Thursday said they believe mosquitoes there are still carrying the virus and the CDC continues to advise pregnant women not to travel to the island. The report also highlights that the greatest incidence of Zika-associated birth defects was apparent among infants born to mothers infected during the first trimester: the results showed that 8% of infants born to Zika-infected mothers in USA territories developed complications compared with 15% of those born in U.S. states.

Zika can be spread by the bite of infected mosquito or via sexual contact.

The researchers were also able to identify varying risks for birth defects based on when during pregnancy the women in the study were infected.

As with the overall group, birth defects in this subgroup were most likely to occur when the mother was infected during the first trimester (8%), followed by the second trimester (5%) and third trimester (4%).

Schuchat said the CDC was using emergency funds set aside for fiscal year 2017 to continue operating the Zika pregnancy registries and could not say how surveillance would be funded in the future as concerns grow that federal support may be withdrawn.

"We must remain vigilant and committed to preventing new Zika infections".

The report represents the largest number of completed pregnancies with laboratory confirmation of Zika infection to date.

"Zika hasn't gone away and while the number of new cases has decreased the virus remains a concern for pregnant women living in the United States territories", said Shuchat.

The exact percentage of infants born with these Zika-linked defects depended on when during pregnancy the woman was infected, according to the U.S. Centers for Disease Control and Prevention report. This report, the first from the U.S. territories, represents the largest number of completed pregnancies with laboratory confirmation of Zika virus infection to date.

Earlier this week, Puerto Rico, which has been struggling to attract tourists during the Zika outbreak, declared the epidemic to have ended.

Among these women, 1,508 had confirmed Zika virus infection from January 1, 2016 to April 25, 2017.

The report comes as Americans in Gulf Coast states and USA territories prepare for a summer mosquito season with the virus still spreading locally in some areas, including Puerto Rico. "This is a very unsafe virus in the context of the pregnancy setting".

"We have also learned that the effects of Zika during pregnancy are not always obvious at birth", Schuchat said, adding that babies may initially look normal but develop signs of Zika complications such as small heads or vision and hearing problems. Island officials blamed a major slump in the industry on news of the Zika virus.

The study found that even infected women without symptoms of the disease were at risk of giving birth to babies with abnormalities.

  • Joanne Flowers