The US Food and Drug Administration (FDA) cautions on blood sample collection

The agency however blood banks can continue collecting and preparing platelets and plasma if an FDA-approved pathogen-reduction technology is used. Current pathogen-reduction technology is not approved to treat whole red blood, which is used for most transfusions. 

The guidelines come as Zika is spreading rapidly through the Americas, with more than 30 affected countries in Latin America and the Caribbean. The virus has been linked to a spike in cases of a rare birth defect known as microcephaly in Brazil, prompting health officials to declare a global health emergency. 

Researchers have begun to study the consequences of Zika transmission through the blood, but that work could take six to 12 months to produce results. In the meantime, the FDA said people at risk of having been infected with the virus defer donating blood for at least four weeks. There is considerable evidence from prior Zika outbreaks that the virus can be transmitted in the blood. What is less clear is whether that transmission causes the recipient to become ill.