More than 500 New Yorkers have been infected with the Zika virus, including 56 pregnant women, according to the NYC Health Department. Although no Zika-carrying mosquitos have been found in New York (yet), health officials are urging New Yorkers—particularly pregnant women and their partners—to refrain from traveling to Zika-infested parts of the world for the next year.

A Department of Health fact sheet shows that the majority of New Yorkers who have been infected with Zika contracted the virus after traveling to the Dominican Republic, but the virus is now being transmitted within the U.S. as well.

Earlier this month, health officials warned pregnant women not to travel to certain parts of Miami Beach; since then, Florida officials have also warned of locally-transmitted Zika cases in the Tampa Bay area. There are up to 270 expected Zika-related microcephaly cases in Puerto Rico, where the virus is also being locally transmitted.

Zika symptoms are mild (the most commonly-reported symptoms are fever, rash, and joint pain), so those infected may not realize they have the virus and could potentially transmit it to their sex partners. Researchers are also investigating the link between Zika and Guillian-Barre Syndrome. Zika can also cause microcephaly, a birth defect that leaves infants with brain damage and abnormally small heads and can cause hearing loss.

The biggest problem researchers are facing with regards to Zika is the unknown. "What we're really challenged with here is a lot of uncertainty," Jay Varma, the Deputy Commissioner for Disease Control at the city's Department of Health said at a press conference last month after the world's first case of a woman sexually transmitting the virus to her male partner.

The FDA recommended last week that all blood donated in the United States and its territories be tested for Zika to prevent more pregnant women from contracting the virus. In 11 states near areas with local transmission or with high rates of travel-related infections, including New York, these new blood testing guidelines must be implemented within four weeks.

As New York continues to prepare for a potential Zika onslaught, the director of the Centers for Disease Control and Prevention warned that federal funds to fight Zika are nearly exhausted.