Blood banks across the United States were told Friday they should start screening donated blood for the Zika virus.
The guidance came from the US Food and Drug Administration (FDA) in a step aimed at keeping the blood supply safe for anyone needing a transfusion, said Peter Marks, director of the FDA’s Center for Biologics Evaluation and Research.
"There is still much uncertainty regarding the nature and extent of Zika virus transmission," Marks said.
The recommendation applies to large blood banks, such as those run by the American Red Cross, and all other smaller entities that collect blood, the FDA said.
The FDA first issued guidance on blood screening in February, recommending it only for areas with active Zika virus transmission.
The FDA said the screening has been shown to be beneficial in identifying donations infected with Zika virus, which is known to cause severe birth defects in children born to mothers who contract the virus.
The Zika virus is transmitted primarily by the Aedes mosquito, but it can also be spread by sexual contact. Four out of five people infected with Zika virus never develop symptoms, which include fever, joint pain and a rash.
Florida, Puerto Rico, American Samoa and the US Virgin Islands have been the focus of US efforts to stop the spread of the virus.
US officials last week warned pregnant women not to travel to Miami Beach, Florida, because of reports of Zika transmission in the area. Prior to the warning the area of concern in Florida had been a single Miami neighbourhood.
Officials in Florida said then five people had contracted Zika from a mosquito bite locally in the state. One week later the number had risen to 42.
Before reaching the US, the virus had seriously affected Latin America, causing hundreds of cases of the birth defect microcephaly there and thousands of suspected cases.