Four more babies born in New York City have been diagnosed with congenital Zika virus syndrome—a manifestation of Zika that can result in brain abnormalities and other birth defects—since the city's first case was reported in July. The Health Department confirmed the five total cases Wednesday as part of a health alert to city doctors.

"Today's news is a reminder that Zika continues to be a threat to pregnant women and their babies," said Health Commissioner Dr. Mary Bassett in a statement. "As we enter the holiday season, we urge all pregnant women in New York City, those who might become pregnant, and their male sexual partners not to visit places where there is active Zika virus transmission."

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, though the virus has also been transmitted in the US (a New York-native mosquito has been found capable of spreading the virus). Zika symptoms are mild—most commonly fever, rash, and joint pain—so those infected may not realize they are sick and could potentially transmit.

According to the city, eight other infants born in NYC have tested positive for Zika to date, though they haven't displayed any of the symptoms associated with the congenital syndrome, which can include an unusually small head (a condition known as microcephaly), abnormalities to the brain or eyes, and irregularly short muscles and tendons.

"We are closely following all babies born to mothers who test positive for Zika infection and will connect parents to available services to improve their child's quality of life," Bassett said.

A total of 325 pregnant women have tested positive or likely for Zika as of December 2nd. This is up from 41 positive test results in July. All of the Zika cases to date have been associated with travel.

NYC has been ramping up its public awareness campaigns throughout the year, and launched a $21 million plan to fight the virus this summer. A new, holiday-themed ad campaign urges New Yorkers to "remain vigilant" when traveling to the Caribbean, Mexico, Central America, South America and parts of Miami-Dade County this winter.

For a powerful reminder of what's at stake, the Cut recently published an account of one family's experience raising a baby with microcephaly in Brazil.