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The D.C. Department of Health says it has confirmed three cases of the Zika virus in the District, WTOP reports.

The first known local victim contracted the mosquito-borne virus in 2015 while traveling to South America, Marcus Williams of D.C.’s health department told WTOP. The other two contracted it this year on trips to South America and Central America. One of these victims was a pregnant woman.

While the virus hasn’t caused any deaths, investigators are researching the link between Zika and babies who’ve been born with microcephaly—a defect in which the baby’s head is smaller than expected. Therefore, officials are especially concerned about pregnant women, going as far as to say they should cancel all travels to countries where the disease has spread.

While the most common way to contract the virus is from the bite of an infected mosquito, there have been a few reports of Zika being spread through blood transfusion and sexual contact (all of these reports are under investigation).

Only 20 percent of people who have the virus get symptoms. The most common of them are fever, rash, joint pain, or red eyes. The World Health Organization estimates that it will infect up to 4 million people by the end of the year in this hemisphere.

Earlier this week, the D.C. Department of Health issued a Zika fact sheet for residents.