Three D.C. residents caught the Zika virus while traveling in Latin America, including one pregnant woman. (WUSA9)

Three people in the District of Columbia, including a pregnant woman, have contracted the mosquito-borne Zika virus.

All three caught the virus while traveling in Latin American countries, which have been most affected by the outbreak that the World Health Organization is calling a global health emergency.

The WHO has said that the virus is “strongly suspected” to cause the birth defect microencephaly, in which babies are born with small heads and may suffer debilitating disabilities.

D.C. Department of Health spokesman Marcus Williams told the Post on Thursday that one case of Zika was confirmed in the District in 2015 and two more, including the pregnant patient, were confirmed in 2016.

(This video was updated on Feb. 2, 2016.) Authorities have confirmed more than 30 cases of Zika virus in the United States. Here's what you need to know. (Gillian Brockell/The Washington Post)

“It is important for residents to remember that there is no immediate threat to their health and well-being if they have not travelled to the known affected areas,” Williams wrote in an email.

The Centers for Disease Control warned this week that in addition to mosquito transmission in affected areas, patients can contract the virus through sex. One patient was infected in Dallas by having sex with someone who had traveled in Venezuela, the CDC said.

Prior to disclosing the three confirmed local cases to several news outlets on Thursday, the D.C. Department of Health issued notices about the virus to health-care providers Jan. 21 and again Monday, and began circulating a fact sheet about the virus at community meetings this week.

But none of those fact sheets mentioned that cases of the virus had been confirmed in the city.

Asked about why the city had not initially informed the public of the three cases, Williams said the health department did not want to “alarm” residents.

“It’s February, it’s not mosquito season … and this isn’t a communicable disease,” Williams said. “We definitely did not want to alarm the public that there has been any immediate threat. But we definitely wanted to inform the public.”

Asked if from now on the District would post updates on confirmed cases of the virus, Williams said it would, but he did not indicate how or with what frequency.

Williams did say that any pregnant woman who has traveled internationally and has symptoms of illness can have blood drawn by their health-care provider and have the sample sent to the CDC for testing for free.