Symptoms of monkeypox patients in the UK differ from those observed in previous outbreaks elsewhere in the world, according to a study published in The Lancet Infectious Diseases journal on Saturday.

The researchers looked at 54 patients who attended sexual health clinics in London, UK and were diagnosed with monkeypox during a 12 day period in May this year.

The finding suggests that patients in this group had a higher prevalence of skin lesions in the genital and anal area and lower prevalence of tiredness and fever than in cases from previously studied outbreaks of monkeypox.

Based on these findings, the researchers suggest current case definitions for 'probable cases' of monkeypox should be reviewed to help identify cases.

They also predict that the high prevalence of genital skin lesions in patients and the high rate of co-occurring sexually transmitted infections means that sexual health clinics are likely to see additional monkeypox cases in the future.

The researchers call for additional resources to support services in managing this condition.

"Currently, the UK and several other countries are seeing a rapid increase in monkeypox cases among individuals attending sexual health clinics, with no apparent links to countries where the disease is endemic," said Nicolo Girometti, from the Chelsea & Westminster Hospital NHS Foundation Trust.

"Monkeypox is a novel diagnosis within the sexual health setting and our study, the first to publish on cases from this UK outbreak, will support future case finding and clinical care, Girometti said.

The researchers collected data from monkeypox patients at four sexual health centres in London, UK.

Confirmed cases were defined as individuals with laboratory-confirmed infection using a RT-PCR test.

They recorded data about the patient's travel history, sexual history, and clinical symptoms.

Individuals diagnosed with monkeypox were advised on isolation measures and regularly assessed subsequently via telephone welfare checks.

The 54 patients observed in this study represent 60 per cent of the cases reported in the UK during the 12 day study period during May this year.

All except two of the patients in the cohort were not aware of having been in contact with a known case and none reported travel to sub-Saharan Africa, however many had recently visited other European countries.

All patients identified as men who have sex with men and there was a median age of 41, the researchers said.

As many as 90 per cent of the patients who responded to the questions on sexual activity reported at least one new sexual partner during the three weeks prior to symptoms, and almost all reported inconsistent condom use in this same time period.

Over half of the patients had more than five sexual partners in the 12 weeks prior to their monkeypox diagnosis, the researchers said.

The patients were all symptomatic and presented with skin lesions; 94 per cent of patients had at least one skin lesion on the genital or perianal skin.

Mostly the patients had a mild illness and recovered while isolating at home, but five individuals required hospital admission due to pain or infection of the skin lesions.

All improved and were discharged with a median of seven days of hospital admission.

"The commonly observed symptom of skin lesions in the anal and penile areas, and the fact that a quarter of the patients tested positive for gonorrhoea or chlamydia at the same time as the monkeypox infection, suggests that transmission of the monkeypox virus in this cohort is occurring from close skin-to-skin, for example in the context of sexual activity," said Ruth Byrne, from the Chelsea & Westminster Hospital NHS Foundation Trust.

The researchers observed important differences in the clinical features of this cohort compared to previous cases reported from earlier outbreaks in other countries.

A lower proportion of patients in the group reported feeling weak and tired or having a fever than in studies on cases in previous outbreaks, the researchers said.

Also, 18 per cent of patients in the group did not report any early symptoms before the onset of skin lesions, they added.