The number of people infected with Zika in Puerto Rico is rising at an alarming rate, putting pregnant women at even greater risk of their babies suffering severe birth defects, a top U.S. public health official said Friday.
The latest data show that the most accurate, real-time indicator of Zika infection suggests that thousands of pregnant women there could contract the virus in the coming months. That, in turn, could lead to "dozens to hundreds of infants born with microcephaly in the coming year," Tom Frieden, director of the Centers for Disease Control and Prevention, said during a media briefing.
The data come from a CDC report showing the percent of Puerto Ricans who are testing positive for Zika during blood donor screening. "These numbers are increasing faster than we had anticipated," Frieden said in a separate interview, referring to the blood-test results. He noted that Puerto Rico has not yet reached the typical peak of mosquito-fueled disease outbreaks, which occurs over the summer and into the fall.
About 1 percent of the island's blood donors tested positive for Zika in the week ending June 11, the highest level since testing began in April, according to the agency's report. The test measures whether someone is infected at that moment. A 1 percent positive rate translates to roughly a 2 percent infection rate each month, Frieden said — which would mean an annual infection rate of about 25 percent for the commonwealth's 3.5 million residents.
Women in Puerto Rico give birth to about 32,000 babies a year. That projected rate of Zika infection would put thousands of pregnant women at risk before they deliver, he said.
His estimate that dozens to hundreds of infants could suffer microcephaly is based on recent research from Brazil. There, doctors found that women who were infected during their first trimester faced as much as a 13 percent risk of giving birth to infants with the rare congenital condition, which is characterized by an abnormally small head and often underdeveloped brain.
Even for the thousands of other Puerto Rican infants who would escape microcephaly, there are additional concerns because "we simply don't know if there will be long-term consequences on brain development," Frieden said.