Blood banks in the United States have begun asking potential donors not to give blood if within the last month they have visited a country in which the Zika virus is spreading.
The aim is to avoid contaminating the blood supply with the virus, said to AABB, the group that represents most blood donation groups in the United States.
Infection of pregnant women with the Zika virus may be linked to microcephaly — unusually small heads — in infants.
The American Red Cross has started to quiz potential donors about recent travel. But other blood banks are simply asking potentially infected donors to stay away.
“We are asking people to make their own judgment,” said Dr. Steven Kleinman, the AABB’s senior medical adviser. “The main thing is, if you have traveled to Mexico, Central or South America, or the Caribbean, people shouldn’t donate blood in first 28 days after their return.”
“It’s very precautionary,” he added. “We expect the large majority of people who return from those areas won’t be infected, but we are casting a wide net.”
Zika virus remains in the blood of an infected person for about a week, according to the Centers for Disease Control and Prevention. There is no approved test that the banks can use to screen donated blood for the virus.
The Food and Drug Administration is developing criteria for deferring blood donors who have visited affected regions, an agency spokeswoman said.
Roughly 3 percent of blood donors tested positive for Zika infection during an outbreak in French Polynesian in 2013, noted the AABB, formerly known as the American Association of Blood Banks.
“The risk posed by Zika virus to the blood supply is unclear,” the organization said in guidance to its members.
Officials at AABB and the American Red Cross said a case of sexually transmitted Zika infection, reported on Tuesday in Dallas, would have no immediate impact on blood donation policies. Neither organization is asking people to abstain from blood donation if they have had sex with a person who recently traveled to a Zika-affected country.
“There is no strong evidence for widespread sexual transmission of Zika,” said Dr. Susan Stramer, vice president of scientific affairs at the American Red Cross.
“We are saying, just postpone donation for 28 days,” she added.
On Tuesday, the C.D.C. began advising pregnant women to avoid contact with semen from men recently exposed to the Zika virus.
On Wednesday, Gov. Rick Scott of Florida declared a public health emergency in four counties where Zika cases were reported. Nine cases have been reported in Miami-Dade, Hillsborough, Lee and Santa Rosa counties, but all of the patients became infected while outside the state.