Despite the spread of Zika across the Americas, United States residents were getting sick only from traveling abroad to countries that have the virus — until now.

A person in Dallas, Texas, caught Zika by having sex with someone who had the virus, most likely acquired on a recent rip to Venezuela, according to Texas health officials. The person who has not traveled outside the United States experienced flu-like symptoms that prompted a visit to the doctor. Blood samples sent to the Centers for Disease Control and Prevention (CDC) confirmed the diagnosis in both people.

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According to a tweet from Tom Frieden, MD, director of the CDC, “This is the first U.S. case of Zika virus infection in a non-traveler in the continental U.S. during current outbreak.”

The revelation promoted the CDC to issue new advice about using condoms, according to CNN. “Sexual partners can protect themselves by using condoms to prevent spreading sexually transmitted infections,” CNN quotes the CDC as saying.

CNN reports: “Earlier Tuesday, CDC Director Tom Frieden told CNN's Chief Medical Correspondent Sanjay Gupta: ‘There have been isolated cases of spread through blood transfusion or sexual contact and that's not very surprising. The virus is in the blood for about a week. How long it would remain in the semen is something that needs to be studied and we're working on that now.’”

The Red Cross also has a new message, this one for blood donors: It asks that people who recently traveled to Zika-ridden areas to wait at least 28 days before giving blood.

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Though it’s possible to catch Zika from sex with an infected partner, the vast majority of cases of Zika are caused by bites from infected mosquitos, officials note. The best protection remains avoiding mosquito bites.

sick with mosquito cdc(Photo: Centers for Disease Control and Prevention/CDC)

Symptoms of Zika virus include rash, fever, joint pain and conjunctivitis, according to the CDC. The illness is usually mild and symptoms typically resolve within a few days to a week.

The Zika virus is currently being actively transmitted in these areas.

Is the United States in for a Zika epidemic?

In a recent blog about Zika virus and what the U.S. government is doing about it, Frieden addressed the question of whether the virus would spread widely in the United States:

“Science doesn’t have a crystal ball, but the CDC has great laboratories and the world’s best disease detectives. For a disease such as Zika to spread widely, two things are necessary. The first is the specific mosquito species that spreads the virus. The second is the conditions in communities; places that are crowded and don’t have air conditioning enable viruses such as Zika to spread.

So we do expect, unfortunately, that Puerto Rico and the U.S. Virgin Islands could have many infections with the Zika virus, and we will certainly see U.S. travelers returning with Zika infections, just as we saw travelers returning with dengue and chikungunya infections. We could see isolated cases and small clusters of infections in other parts of the country where the mosquito is present. But from the information we know now, widespread transmission in the contiguous United States appears to be unlikely.”

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Marianne has been producing content that informs and inspires for more than 20 years, with a deep focus on bringing readers accurate, actionable advice and helping them live healthier, safer lives. Before launching SafeBee, she was executive editor of Sharecare, the health website and social network. Previously, she developed more than two dozen illustrated consumer health books for Reader’s Digest. Her writing has appeared in numerous outlets including Arthritis Today and WebMD. Her favorite safety tip: Know the purpose of every medication you take and under what circumstances you can stop taking it.