A pregnant woman is one of three people in New York City who are infected with the Zika virus, it was revealed Thursday.
There are 31 confirmed diagnoses of the mosquito-borne illness, believed to cause birth defects, in the United States.
All of them are believed to have caught the infection, which is transferred by the Aedes mosquito, while traveling in the Caribbean or Latin America where there are outbreaks of the tropical illness.
Four other people in New York state, in Monroe, Nassau, Suffolk and Orange counties, have been diagnosed with the virus, according to NBC.
The latest update came on the day the scientists warned Zika has an 'explosive pandemic potential', and could impact up to four million people.
For most people who get infected, the flu-like symptoms will clear up in about a week, but the virus has also been linked to microcephaly - a birth defect which results in an abnormally small head.
There are now fears the 2016 Rio Olympics could be affected because of a spike in cases, with some athletes being warned not to go.
Zika cannot be transmitted by casual person-to-person contact. While there is concern that Zika virus may be sexually transmitted, officials at the Centers for Disease Control (CDC) have said the evidence of sexual transmission is insufficient.
Officials said Thursday the 31 people are in 11 states and Washington. In US territories, Puerto Rico has 19 confirmed cases and the US Virgin Islands has one.
Barbados, Bolivia, Brazil, Colombia, Cape Verde, the Dominican Republic, Ecuador, El Salvador, French Guiana, Guadalupe, Guatemala, Guyana, Haiti, Honduras, Martinique, Mexico, Panama, Paraguay, Saint Martin, Samoa, Suriname, Venezuela, all have ongoing Zika transmission.
Canada and Chile are the only countries in the Americas the virus is not expected to reach, the WHO said on Monday.
United Airlines and American Airlines have since announced they will allow customers with tickets to Zika-affected countries to postpone or cancel their trip without penalty.