The case pertains to a young adult male who sought care in the Denver area and is reportedly isolating and improving at home.
The first possible case of monkeypox was found in a person who had recently traveled to Canada.
The Centers for Disease Control and Prevention (CDC) tracker shows two cases nationwide, including two in Colorado, and California. Florida and Utah.
Washington, Massachusetts, New York, and Virginia all have a case, according to agency data.
The World Health Organization (WHO) said on Friday that nearly 200 cases of monkeypox have been reported around the world, with cases in more than 20 countries that do not usually cause outbreaks of the virus.
Traditionally, the monkeypox virus is transmitted by touching or biting infected wild animals in western and central Africa.
However, the former World Health Organization (WHO) emergency department leader told The Associated Press earlier this week that cases in Europe appear to be spreading through sexual activity in Spain and Belgium.
Although it is not a sexually transmitted infection, it can be transmitted in both personal and sexual contact, with a notable fraction of recorded cases among gay and bisexual men.
To treat monkeypox, few smallpox vaccines and therapeutics are available – no vaccine has been specifically developed against monkeypox – and the WHO proposed creating a stockpile to equitably share what was available.
The CDC said last week that the Strategic National Stockpile has doses of a vaccine to prevent the monkeypox virus and that production will “step up” rapidly in the coming weeks.
Symptoms of the virus — which are from the family of viruses similar to smallpox — include fever, chills, rash, and pain before sores develop.
Most patients recover within several weeks without the need for hospitalization.