There were “no signs of a decline" in the monkeypox epidemic and the virus “continues to be transmitted primarily in interconnected sexual networks of gay, bisexual, or men who have sex with men," the health agency in a review of the outbreak published last week said.
The Health Security Agency said 97% of cases fell in that category and that there was no evidence of sustained transmission beyond that.
Earlier the scientists had warned that anyone who is in close physical contact with someone who has monkeypox or their clothing or bedsheets is at risk of infection, regardless of their sexual orientation.
The scientists estimate the outbreak is doubling in size about every two weeks and said it's likely cases are being undercounted.
They said that in nearly 80% of cases, there is no information about whether or not the person had contact with a confirmed case, meaning the virus is spreading undetected.
Scientists said the monkeypox virus has been spreading through close or sexual contact. There has been no evidence of airborne transmission, they added.
Scientists also noted that people with unusual symptoms, including only a single lesion, have been detected in the outbreak and say there have also been reports elsewhere of people with no symptoms carrying monkeypox.
The health agency said the number of cases and countries identifying monkeypox “continues to increase steeply," saying that infections beyond Africa have also been primarily seen in gay and bisexual men. It said there had been three cases of monkeypox in children, who are more likely to suffer serious disease.
Last month, the World Health Organization declined to declare monkeypox a global health emergency, but said it would revisit its decision soon.
The global health body said its evaluation of the outbreak could change if there are cases among sex workers, if the virus continues to spread rapidly or if more severe disease is seen.
About 10% of infected people in the UK have been hospitalized, but there have been no deaths reported.
People with monkeypox often experience symptoms like fever, body aches and a rash; most recover within weeks without needing medical care.
