The zika virus is spreading quickly in Puerto Rico, meaning hundreds of babies could be born with birth defects, NBC News reports.
More than 1 percent of all Puerto Rico blood donations tested in early June tested positive for the virus, according to the Centers for Disease Control and Prevention.
"In coming months, it is possible that thousands of pregnant women in Puerto Rico will catch Zika," CDC director Dr. Thomas Frieden said at a briefing for reporters. "This could lead to dozens or hundreds of infants being born with microcephaly in the coming year."
The CDC began testing for Zika in Puerto Rico in April. Health officials confirmed more than 1,700 infections in the territory so far this year. Any blood donations that test positive for the virus are thrown out.