Health officials in Utah are investigating two suspected cases of Monkeypox, the fourth US state to report infections.
Two adults who live in the same house in Salt Lake County and had recently returned from overseas are showing mild symptoms for the disease, officials said.
Salt Lake Health said the infected pair were isolating and there was not thought to be any risk of exposure to others.
Five confirmed or suspected cases have now been reported in the US in the past week.
In Massachusetts, the CDC said it was monitoring more than 200 contacts of a Boston patient, with the majority being healthcare workers, the Boston Herald reported.
On Sunday, Florida health officials said they had identified a “presumptive” case of Monkeypox in a patient in Broward County. The case was also linked to international travel.
Last week a Massachusetts man became the first confirmed case in America. Samples from a patient in New York City who was experiencing symptoms consistent with Monkeypox are also being examined by the Centers for Disease Control and Prevention.
World Health Organisation (WHO) official David Heymann said on Monday the leading theory on how the current outbreak is being spread was sexual contact among gay and bisexual men who attended two recent raves in Spain and Belgium.
Monkeypox is relatively common in Africa, where it is endemic in animals, but has not previously triggered outbreaks beyond the continent.
“We know monkeypox can spread when there is close contact with the lesions of someone who is infected, and it looks like sexual contact has now amplified that transmission,” Dr Heymann said.
President Joe Biden delivered a more reassuring message to reporters in Tokyo on Monday, a day after he had said “everybody should be concerned” about the disease.
He said the smallpox vaccine was effective against Monkeypox, and the US has sufficient doses on hand to deal with an outbreak.
“I just don’t think it rises to the level of the kind of concern that existed with COVID-19,” he said during a news conference.
The WHO have detected 190 confirmed or possible cases across 16 countries including Britain, Spain, Israel, France, Switzerland, and Australia.
On Monday, Denmark announced its first case, Portugal revised its total upwards to 37 and Italy reported one further infection. which spreads from primates to humans.
US health officials say the risk remains low in the United States. They have recommended anyone travelling to countries in Europe and West Africa where Monkeypox was active should consider getting immunised.
Associated Press contributed to this report
