The Centers for Disease Control and Prevention today issued updated guidelines for testing pregnant women who live in or travel to areas with ongoing Zika virus transmission, and new guidelines for preventing sexual transmission of the virus. Thirty-five travel-associated cases of Zika virus have been detected in 11 states and the District of Columbia since 2015. Another 10 cases have been reported in Puerto Rico and the U.S. Virgin Islands, all but one of them locally acquired. Recent evidence suggests a possible association between maternal Zika virus infection and adverse fetal outcomes, such as microcephaly. Until more is known, CDC strongly advises pregnant women to consider postponing travel to Zika-affected areas, or talk to their health care provider before they do and strictly follow steps to avoid mosquito bites during the trip. Only about one in five people infected with the mosquito-borne virus will get sick, and their illness is usually mild. There are currently no vaccines or medications to prevent or treat Zika infections. As a precaution, both the American Red Cross and AABB this week recommended individuals refrain from donating blood for 28 days after traveling to Zika-affected areas. For more information, visit www.cdc.gov/zika and www.aha.org/zika.