Pregnant Woman in NYC Is One of 31 Infected With Zika Virus in US

PHOTO: Aedes aegypti mosquitoes sit in a petri dish at the Fiocruz institute in Recife, Pernambuco state, Brazil, Jan. 27, 2016.PlayFelipe Dana/AP Photo
WATCH Zika Virus Said to Be 'Spreading Explosively'

At least 31 people in the U.S. have been diagnosed with the Zika virus in 11 states, including a pregnant woman in New York City, according to the Centers for Disease Control and Prevention.

Two other pregnant women were diagnosed with the disease in Illinois earlier this month.

Health officials noted that all those infected likely contracted the disease outside of the U.S. There is no current transmission of the virus in the country.

There have been reports of transmission in Puerto Rico and the U.S. Virgin Islands, where at least 20 people have been diagnosed with the virus.

Three people in New York City, including one pregnant woman, have been diagnosed with the virus, health officials said Thursday.

"Because Zika virus is primarily transmitted by infected mosquitoes, there is very limited chance of local transmission in New York during the winter," New York Health Commissioner Dr. Howard Zucker said in a statement. "Even so, the Department of Health is taking steps now to protect the health of all New Yorkers and to prepare for the warmer months when mosquitos will be active in New York."

The CDC has advised doctors to monitor infected pregnant women to see if their infants show signs of microcephaly in utero. The birth defect is characterized by a small head and brain, and can result in developmental delays.

The Boston Health Department also confirmed its first case of Zika virus in the city on Thursday. Boston health officials said they expect the patient to make a full recovery.

"The species of mosquito that transmits Zika is rarely found in Boston," Dr. Anita Barry, director of the Infectious Disease Bureau at the Public Health Commission, said in a statement. "However, we encourage those traveling to countries with a high risk for Zika transmission -- especially those who are pregnant or may become pregnant -- to take the utmost care to avoid contracting the virus."

Others states with a confirmed cases include Texas, Hawaii, Florida, Illinois, New Jersey, Arkansas, Virginia, California and Minnesota.

The CDC has issued a travel alert for 24 countries and territories where the virus transmission is ongoing.

Those countries and territories are: Brazil, Colombia, El Salvador, French Guiana, Guatemala, Haiti, Honduras, Martinique, Mexico, Panama, Paraguay, Suriname, Venezuela, Puerto Rico, U.S. Virgin Islands, Dominican Republic, Barbados, Bolivia, Ecuador, Guadeloupe, Saint Martin, Guyana, Cape Verde and Samoa.

Get real-time updates as this story unfolds. To start, just "star" this story in ABC News' phone app. Download ABC News for iPhone here or ABC News for Android here.