Doncaster and Bassetlaw Teaching Hospitals NHS Trust says a patient who visited Doncaster Royal Infirmary at the start of August has tested positive for the virus.
All contacts of the person concerned have been reviewed and a small number of people, who are considered low risk, are being contacted. They are also being offered vaccination.
Dr Ken Agwuh, the trust's director of infection, prevention and control (IPC), said: "We can confirm that an individual who attended Doncaster Royal Infirmary (DRI) in early August has subsequently tested positive for monkeypox.
"Following confirmation of this diagnosis, we have reviewed all contacts with the individual, using the relevant guidance and with the support of national and regional experts. As a precautionary measure, we are now contacting a small number of people, all of whom are considered low risk, to offer them support and vaccination if appropriate.
"All contacts occurred in a very specific area of the hospital and please be assured that there is not considered to be any risk to anyone else who has recently been treated at, or visited DRI, and unless you have been contacted by us directly by phone call you do not need to do anything."
It comes after it was announced that the UK will receive around 100,000 doses of smallpox vaccine to treat monkeypox, following reports the country is poised to run out.
What is monkeypox?
Monkeypox is a rare infection. It is mainly spread by wild animals in parts of west or central Africa, which is what makes the recent cases elsewhere in the world unusual.
In Europe, North America and elsewhere, monkeypox is spreading among people with no links to animals or recent travel to Africa.
There have been 67 recorded cases of monkeypox across the Yorkshire and Humber region since the start of May. Over 3,000 cases have been recorded in England.
What are the symptoms?
It usually takes between five and 21 days for the first symptoms of the infection to appear.
The first symptoms of monkeypox include:
a high temperature
A rash, which often begins on the face before spreading, usually appears one to five days after the first symptoms.
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