Thirty-one travel-associated cases of Zika virus have been detected in 11 states and the District of Columbia since 2015, Anne Schuchat, M.D., principal deputy director of the Centers for Disease Control and Prevention, said during a media briefing today, adding that information on the specific states would be forthcoming. Another 19 laboratory-confirmed cases have been reported in the territory of Puerto Rico and one in the U.S. Virgin Islands, some of which may be locally acquired, she said. A marked increase in infants born with microcephaly, a birth defect resulting in smaller than normal head size, has been reported during the Zika outbreak in Brazil. It is not known how many of the cases are associated with the virus. 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. While there are currently no vaccines or medications to prevent or treat Zika infections, the National Institutes of Health is working with partners to accelerate research on diagnostic tools, vaccines and therapeutics, said Anthony Fauci, M.D., director of the National Institute of Allergy and Infectious Diseases. For more information, including interim guidelines for U.S. health care workers, visit www.cdc.gov/zika and www.aha.org/zika. Hospital leaders today received a Readiness Advisory with more information.