The U.S. Food and Drug Administration recommended on Friday that all blood donated in the United States and its territories be tested for Zika virus, as it moves to prevent transmission of the virus through the blood supply.

The agency said its move to expand blood screening in the United States was based on concerns about increasing cases of local transmission in Florida, the growing number of travel-related infections and concerns that Zika-tainted blood could unwittingly be given to a pregnant woman, putting her unborn baby at risk of severe birth defects.

“The transfusion of a pregnant woman with blood infected with the Zika virus could have terrible consequences,” Peter Marks, director of the FDA’s Center for Biologics Evaluation and Research, said in a conference call with reporters.

The current Zika outbreak was first detected in Brazil last year and has since spread across the Americas. In Brazil, Zika has been linked to more than 1,800 cases of microcephaly, and U.S. officials expect as many as 270 cases in Puerto Rico, where local transmission of the virus is widespread.

“Over 8,000 travel associated and over 2,000 non-travel associated cases of Zika have been reported in the United States and U.S. territories,” Marks told reporters.

Given frequency of travel of individuals within the United States, he said there is a risk that people without symptoms of Zika could donate blood and transmit the virus.

Marks said the FDA plans to roll out its recommendations in stages. In states and territories with local, mosquito-borne transmission, the recommendations go into effect immediately. This impacts Florida and Puerto Rico.

In 11 states near areas with local transmission or high rates of travel-related infections, the guidelines must be implemented within four weeks. These states include: Alabama, Arizona, California, Georgia, Hawaii, Louisiana, Mississippi, New Mexico, New York, South Carolina and Texas.

For the rest of country, the guidelines must be implemented within 12 weeks.

Marks said Hologic Inc and Roche Molecular Systems have been granted special approval to have their tests used to screen the blood supply.

Marks said the FDA has already reviewed data submitted by these companies and is confident these investigational tests “will perform appropriately” in this setting.

In addition to tests to check whole blood for Zika RNA, the FDA said blood collection centers may use Cerus’ Intercept pathogen inactivation system in certain blood products, such as plasma.

Dr. Alyssa Ziman, medical director of the clinical laboratories and transmission medicine at the University of California Los Angeles, said the new recommendations for Zika follow the similar steps the FDA took to protect the blood supply from the West Nile virus.