CHICAGO (Reuters) - The first report on how the Zika virus affected U.S. territories showed that 5 percent of women with confirmed infections had babies with birth defects, U.S. health officials said on Thursday.
The report from the Centers for Disease Control and Prevention is the first to include official numbers from the territory of Puerto Rico, which on Monday declared that its Zika epidemic had ended, based on data showing the number of new cases has fallen.
The CDC on Thursday reiterated its recommendation that pregnant women not travel to Puerto Rico, noting that Zika remains a risk for pregnant women there and anywhere else the mosquito-borne virus is active.
"Zika virus poses a serious threat to pregnant women," said CDC Acting Director Dr Anne Schuchat.
"Women in the U.S. territories and elsewhere who have continued exposure to mosquitoes carrying Zika are at risk of infection. We must remain vigilant and committed to preventing new Zika infections."
The report reviewed 2,549 cases of women with possible Zika infection who completed their pregnancies, of which 1,508 had confirmed infections. Besides Puerto Rico, the cases came from American Samoa, the Federated States of Micronesia, the Republic of Marshall Islands, and the U.S. Virgin Islands from Jan. 1, 2016, through April 25, 2017.
Of these confirmed cases, more than 120 pregnancies, or about 5 percent, resulted in Zika-associated birth defects, the CDC said in its Morbidity and Mortality Weekly Report.
Among the women infected during their first trimester of pregnancy, 8 percent had babies with Zika-associated birth defects. That compared with 15 percent in a prior study of birth defects among women from U.S. states and the District of Colombia, most of whom became infected during travel to Zika-affected countries.
The CDC said because the newer report is much larger, the findings are not statistically different.
About 5 percent of women infected during their second trimester and about 4 percent infected in their third trimester had babies with Zika-related birth defects, showing the virus remains dangerous throughout a woman's pregnancy.
The report represents the largest number of completed pregnancies with lab-confirmed Zika virus infections to date.
The CDC had stopped reporting Zika pregnancy outcomes for U.S. territories last fall because not all were using the same case definitions. Puerto Rico has its own Zika pregnancy registry. In its June 2 report, Puerto Rico's health department listed 38 cases of birth defects among more than 3,700 Zika-affected pregnancies.
Peggy Honein, who leads the CDC's Zika pregnancy and birth defects task force, said the CDC in late June will resume regular reporting of the number of completed pregnancies and birth defects from U.S. territories.
Honein said in a conference call with reporters that each jurisdiction may keep its own website using its own case definitions, but as of June 22, all U.S. territories will be using the same standard as the CDC case definition for U.S. states and the District of Columbia in the CDC registry.
Schuchat said on the call the CDC is paying for the pregnancy registry using emergency funds allocated for Zika last year. She declined to speculate about future funding. The Trump administration has proposed a 17 percent cut in CDC's budget for fiscal 2018, its smallest in 20 years.
As mosquito season ramps up in the continental United States, scientists predict local transmission is likely to occur only in the two areas where it was active last year - Miami and Brownsville, Texas. That is because Aedes aegypti mosquitoes are present in those two locations year-round, Kristian Andersen of the Scripps Research Institute in La Jolla, California, reported in the journal Nature.
Editing by Bernard Orr and Matthew Lewis