The UK Health Security Agency (UKHSA) has detected 11 additional cases of monkeypox in England.
The latest cases bring the total number of monkeypox cases confirmed in England since 6 May to 20.
The infection can be passed on through close contact or contact with clothing or linens used by a person who has monkeypox.
However, the virus does not usually spread easily between people and the risk to the UK population remains low.
Anyone with unusual rashes or lesions on any part of their body, especially their genitalia, should contact NHS 111 or call a sexual health service if they have concerns.
A notable proportion of early cases detected have been in gay and bisexual men and so UKHSA is urging this community in particular to be alert.
People should notify clinics ahead of their visit and can be assured their call or discussion will be treated sensitively and confidentially.
Monkeypox is usually a mild self-limiting illness, spread by very close contact with someone with monkeypox and most people recover within a few weeks.
Dr Susan Hopkins, Chief Medical Adviser, UKHSA, said:
“We anticipated that further cases would be detected through our active case finding with NHS services and heightened vigilance among healthcare professionals.
“We expect this increase to continue in the coming days and for more cases to be identified in the wider community. Alongside this we are receiving reports of further cases being identified in other countries globally.
“We continue to rapidly investigate the source of these infections and raise awareness among healthcare professionals. We are contacting any identified close contacts of the cases to provide health information and advice.
“Because the virus spreads through close contact, we are urging everyone to be aware of any unusual rashes or lesions and to contact NHS 111 or a sexual health service if they have any concerns.
“Please contact clinics ahead of your visit and avoid close contact with others until you have been seen by a clinician.
“A notable proportion of recent cases in the UK and Europe have been found in gay and bisexual men so we are particularly encouraging them to be alert to the symptoms and seek help if concerned.
“Clinicians should be alert to any individual presenting with unusual rashes without a clear alternative diagnosis and should contact specialist services for advice.”
Initial symptoms of monkeypox include fever, headache, muscle aches, backache, swollen lymph nodes, chills and exhaustion.
A rash can develop, often beginning on the face, then spreading to other parts of the body including the genitals.
The rash changes and goes through different stages – it can look like chickenpox or syphilis, before finally forming a scab which later falls off.