The Centers for Disease Control and Prevention believe five cases of monkeypox have been found in the U.S. — including a case in New York City — according to an announcement Monday. The federal agency is advising health care providers to treat these incidents as true positives as it conducts follow-up testing and is conducting outreach within potentially vulnerable populations.

The update follows an announcement Friday from the city health department and New York State health officials that one of two suspected monkeypox patients had tested positive for “Orthopoxvirus, the family of viruses to which monkeypox belongs.” They said the incident was being treated as a “presumptive positive,” meaning it needed secondary confirmation by the CDC.

“I want to emphasize that we’re in the early days of this response. It’s likely that there are going to be additional cases reported in the United States,” Dr. Jennifer McQuiston, a veterinarian and deputy director of division of High Consequence Pathogens and Pathology at the CDC’s National Center for Emerging and Zoonotic Infectious Diseases, said during a briefing on Monday. “The CDC is poised to help our state health partners learn more about how the cases are occurring and how we can help bring these outbreaks under control.”

When monkeypox spreads from person to person, it is typically through close sustained skin-to-skin contact with someone with an active rash — or through respiratory droplets from someone who has lesions in their mouth. It can also spread from infected animals or contaminated materials. Monkeypox symptoms are flu-like and include fever, headache and muscle soreness. But it is characterized by swollen lymph nodes and rash-like lesions that appear throughout the body

“What we’re talking about here is close contact. It’s not a situation where you’re passing someone in the grocery store, [and] they’re going to be at risk for monkeypox,” McQuiston said.

There is currently one confirmed monkeypox case in Massachusetts. In addition to the presumptive case in New York City, two others are suspected in Utah, as well as one in Florida. The CDC is expecting to receive samples of the four possible cases between Monday and Tuesday for confirmation testing.

During Monday’s briefing, CDC medical epidemiologist Dr. John Brooks said that while anyone can develop monkeypox, many of those affected in the current outbreak identify as gay and bisexual men.

“Awareness of this reality is critical to empowering people to make informed decisions about their personal health and the health of their community,” Dr. Brooks said.

He said though monkeypox is not a sexually transmitted infection in the typical sense, it could spread through intimate contact or shared bedding. He urged anyone with a new or unexplained rash to see their doctor or seek evaluation.

“Some groups may have a greater chance of exposure right now. But by no means [is] the current risk of exposure to monkeypox exclusively to the gay and bisexual community in the U.S.,” Dr. Brooks said.

These developments follow a string of outbreaks in Europe. The World Health Organization on Monday, without citing evidence, blamed the European outbreaks on sex at two large raves in Spain and Belgium, according to the Associated Press. The WHO states that more than 90 cases have been reported worldwide since May 13th, most in Europe. According to Dr. McQuiston, this outbreak is different from ones in the past because most cases don’t have recent travel records to countries in West or Central Africa, where the disease is typically found.

The best way to deal with cases, health experts say, is to isolate if infected and to follow up with anyone who came in close contact with a patient. Health care providers are advised to tell close contacts to watch for symptoms and isolate if they experience any signs..

According to the CDC, people usually recover within 2 to 4 weeks without specific treatment. Antiviral medication can curb infections already in progress, and the CDC says it has more than 100 million doses of smallpox vaccine on hand to contain future outbreaks.

Outside of smallpox, which has been eradicated globally through vaccination, only monkeypox and cowpox are members of the Orthopoxvirus family that are thought to cause human disease. The smallpox vaccine offers cross-protection against monkeypox. Cowpox has never been reported in the U.S. and isn’t thought to spread person-to-person.

This story has been updated with additional information.