New Yorkers who have traveled to South Florida will be barred from donating blood for 28 days as collection centers begin crafting rules to keep Zika virus out of the blood supply.

Zika, a mere footnote in reports by blood center medical experts a year ago, has become a pathogen of extreme importance in recent months, experts said Tuesday.

Dr. Lou Katz, chief medical officer of America’s Blood Centers of which the New York Blood Center is an affiliate, said there are two screening tests under study by federal scientists that are capable of spotting Zika in a donated blood sample. They were so far along in development, Katz said, they have been deployed in Zika hot spots in the Caribbean.

The few tests that exist have been shipped to Florida and elsewhere on the Gulf Coast where Aedes aegypti, a Zika-carrying mosquito, is believed to be spreading the virus.

The New York Blood Center collects all blood types and blood products through a network of affiliated sites in Nassau and Suffolk counties. Other institutions and nonprofit organizations on the Island, such as the Red Cross and local hospitals, also collect and bank blood. The products enter the general supply and are used for a variety of purposes, from meeting surgical needs to providing blood for people who have injuries and are transfused in emergency rooms.

Zika’s unexpected emergence in recent months has forced blood centers to quickly cobble together a set of new rules.

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“We are taking every precaution,” Katz said of making certain that Zika does not cause infection through transfused blood. He and other experts in blood banking said every two seconds somewhere in the United States someone needs a transfusion.

Katz said it took five years after the emergence of the AIDS epidemic in the 1980s for scientists to develop a screening to detect HIV in the nation’s blood supply, but only nine months for experts to develop a test to screen for West Nile. With Zika, it took just two months to develop tests that spot it in a blood sample.

The two tests still under study but already in use have been identified as a Zika screening strategy developed by pharmaceutical giant Roche; the other was designed by the medical diagnostics company, Hologic in collaboration with its Spanish partner, Grifols.

Despite being under investigation by the U.S. Food and Drug Administration, the tests were deemed critically needed when several people in South Florida became infected with Zika without evidence of having traveled to Latin America or the Caribbean. The cases strongly suggested mosquitoes in the area were carrying the pathogen.

The Centers for Disease Control and Prevention, working with the Florida Department of Health, confirmed four locally transmitted cases of Zika last week in Miami-Dade and neighboring Broward counties. All of the infections were acquired in the same section of Miami. Ten more cases were confirmed by the CDC on Monday.

Dr. Peter Marks, director of the FDA’s Center for Biologics Evaluation and Research, says his agency is working closely with several companies that are making blood screening tests to make sure screening can be expanded.

Last week the agency requested that blood collection centers South Florida cease blood collection to keep the supply safe.

Marintha Heil, director of the Roche molecular diagnostics division, said in a statement that her company saw a growing need for a screening after transfusion cases were documented in Brazil.

“At the beginning of this year, a Roche molecular diagnostics research team started designing a blood screening test. Several candidate detection sets and controls were synthesized and tested.”

Katz said with so much travel between New York and South Florida, he expects a 2 percent drop in blood donations because of the 28-day waiting period for donations from people who have traveled to the Sunshine State.