The U.S. Centers for Disease Control and Prevention issued a travel advisory on Wednesday warning pregnant women to consider postponing travel to Brownsville, Texas, because of the risk of contracting Zika.
The advisory, issued through CDC's Health Alert Network, follows reports of infections in five people living in the Brownsville area who have contracted Zika through local mosquitoes, suggesting an ongoing risk of Zika infection.
“We are working closely with Texas to gather and analyze new information every day," CDC Director Dr. Tom Frieden said in a statement.
Frieden said Zika appeared to have been spreading in the Brownsville area "for at least several weeks," which prompted the agency to issue the warning and urge pregnant women who live and work in the area to take steps to prevent mosquito bites.
Texas is one of several U.S. states where Aedes aegypti mosquitoes, which carry Zika, are present. It is the second state within the continental United States after Florida to report local transmission of the virus that has been linked to birth defects.
The CDC said there was currently no evidence of widespread transmission of Zika, but temperatures are still warm enough in the Brownsville area - located near the Mexico border - to support mosquito-borne transmission of the virus, which has been shown to cause birth defects.
The advisory says that pregnant women in the area are at some risk of Zika, but the extent of risk is unknown.
It urges pregnant women, women of reproductive age and their partners who live in or have traveled to Brownsville on or after Oct. 29, 2016, to get tested for Zika.
Women who have been exposed to Zika through visiting the area, or unprotected sex with someone who has visited, should wait eight weeks before attempting to conceive.
Men who have been exposed in the same way should consider waiting at least six months before attempting to conceive a child to prevent sexual transmission of the virus.
Earlier on Wednesday, the CDC released a study showing that 6 percent of fetuses or infants whose mothers were infected with Zika during pregnancy developed birth defects, including microcephaly, in which the baby has an undersized head and brain.
The connection between Zika and microcephaly first came to light last year in Brazil, which has since confirmed more than 2,200 cases of the birth defect.
(Reporting by Julie Steenhuysen; Editing by Bernard Orr and Tom Brown)