SACRAMENTO, Calif. -- Two babies have been born with Zika-related birth defects in California to mothers who were infected overseas, health officials said Thursday.The newborns survived. One of the mothers returned to her home country with her baby while the other remains in the state, according to the California Department of Public Health.Health officials declined to release additional details about the cases, citing patient privacy.Nineteen other pregnant women in California who contracted Zika while traveling abroad were being monitored by doctors.Babies born to Zika-infected mothers will be followed for up to a year. Health officials will check their hearing, vision and development, said Dr. Connie Mitchell, deputy director of the Center for Family Health.Nationwide, 13 babies have been born with Zika-related birth defects, according to the federal Centers for Disease Control and Prevention.The CDC has advised pregnant women not to travel to parts of Latin America and the Caribbean where Zika transmission is active. The virus is usually spread by mosquitoes, but it can also be passed through sex.Most people infected with Zika experience mild symptoms such as fever, rash and joint pain. Zika infection during pregnancy can cause babies to be born with unusually small heads, called microcephaly.Florida is the only U.S. state so far that has reported homegrown Zika transmission by mosquitoes in a square-mile neighborhood in Miami-Dade County. The CDC has urged expectant mothers to avoid Miami's Wynwood neighborhood, where at least 15 people are believed to have been infected with the Zika virus through mosquito bites.