Monkeypox patients in Britain have noticeably different symptoms from those seen in previous outbreaks, raising concerns cases are being missed, researchers in London said on Friday.

Britain researchers analyzed 54 monkeypox patients in London, all men who had sex with men and all but two were unaware they had been in contact with someone who had the disease.

Only 57 percent of patients suffered fevers, much lower than the 85 to 100 percent of cases in outbreaks before this year.

All patients had skin lesions, of which 94 percent were in the genital and anal areas. Previous outbreaks saw far more lesions on limbs, faces and necks.

These patients also had mostly mild cases lasting fewer than three days, with just five being hospitalized.

A quarter of the patients were HIV-positive and a quarter had a sexually transmitted disease at the same time they had monkeypox.

The authors said case definition of monkeypox symptoms in UK, which was described as an acute illness with a fever, should be reviewed to avoid cases being overlooked, particularly as monkeypox can "mimic" other common sexually transmitted infections.

"At least one in six of this cohort would have not met the current 'probable case' definition," said Nicolo Girometti, lead author of the study, from Chelsea & Westminster Hospital NHS Foundation Trust.

The study was published in The Lancet Infectious Diseases journal.

The total number of confirmed cases of monkeypox in the UK reached 1,076 as of June 26, according to figures updated by its Health and Security Agency on July 1.

(With input from agencies)