Tom Frieden warned in May that the window of opportunity to keep Zika from spreading within the mainland United States was rapidly closing. (Image: YouTube screen capture/AP)

(Bloomberg) — Women who are pregnant or thinking of becoming pregnant should avoid travel to an area in Miami that is the center of a small-but-growing number of mosquito-transmitted Zika cases, the U.S. Centers for Disease Control and Prevention said Monday.

“We may well see other infections in that area,” CDC Director Tom Frieden said during a conference call with reporters where he issued the warning. The CDC has sent an emergency team to the state to assist in efforts to fight the virus, and Frieden said that pregnant women who have been in the area after June 15 should talk to a doctor and get tested.

Related: CDC chief on Zika: ‘The window of opportunity is closing’

Florida Department of Health officials said Monday they’ve identified at least 14 cases of Zika in Miami that were transmitted by mosquito. They’re the first known cases of local mosquito transmission in the U.S., where most cases have been traced to travel outside the country. The state said that all of the known transmissions are thought to have occurred in an area of Miami about a square mile in size.

The virus can cause birth defects when pregnant women become infected, though most adults have only mild symptoms, if they know they’re sick at all. The CDC recommended that women who’ve visited the area not get pregnant for 8 weeks after returning.

The government warning is a further sign of how seriously health officials are taking the virus in the U.S., where its spread has mostly been limited to cases imported into the U.S., or transmitted through sexual contact. Experts have warned that limited outbreaks in the U.S. are likely, and women have been warned not to vacation in countries or regions in South and Central America where the infection is already widespread.

Tourism is big business in Miami, and in 2015 15.5 million visitors stayed overnight in the greater Miami area, according to a report by the Greater Miami Convention and Visitors Bureau. The warning could impact the hotel and leisure industry if people avoid the city’s beaches, clubs and restaurants.

Related:

Could Zika paralyze hundreds of U.S. adults?

Zika virus does cause birth defects

Have you followed us on Facebook?

Copyright 2018 Bloomberg. All rights reserved. This material may not be published, broadcast, rewritten, or redistributed.