Higher prevalence of skin lesions in the genital and anal area and lower tiredness and fever were seen among new monkeypox patients than among those infected during previous outbreaks of the virus, according to a study published in The Lancet Infectious Diseases.
To date, more than 5,000 monkeypox cases have been reported from 51 countries worldwide not endemic to the disease, according to the US Centers for Disease Control and Prevention.
The number of infections in Europe represents about 90 per cent of the global total, with the UK reporting 1,235 cases - the highest in the continent.
Researchers from the Chelsea & Westminster Hospital NHS Foundation Trust looked at 54 patients who attended four sexual health clinics in London and were diagnosed with monkeypox during a 12-day period in May 2022.
Of the 54 patients, all except two of the patients were not aware of having been in contact with a known case and none reported travel to sub-Saharan Africa, but many had recently visited other European countries.
All patients identified as men who have sex with men, and 47 of 52 reported at least one new sexual partner during the three weeks prior to symptoms, and 49 of 52 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 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 whilst 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 gonorrhea 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 Dr. Ruth Byrne, from the Trust.
She added that "it is possible that at various stages of the infection monkeypox may mimic common STIs, such as herpes and syphilis, in its presentation.
It's important that sexual health clinicians and patients are aware of the symptoms of monkeypox as misdiagnosis of the infection may prevent the opportunity for appropriate intervention and prevention of onward transmission".
The study also 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 this cohort reported feeling weak and tired and/or having a fever than in studies on cases in previous outbreaks.
In addition, 18 per cent (10/54) of patients in this cohort did not report any early symptoms before the onset of skin lesions.
"Given the suggested route of infection via contact during sexual activity and the number of clinical findings differing from previous descriptions, we suggest that case definitions currently detailing symptoms such as acute illness with fever should be reviewed to best adapt to the current findings, as at least one in six of this cohort would have not met the current 'probable case' definition," said Dr. Nicolo Girometti, from the Trust.
The researchers 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.
However, the team cautioned that their findings might not be representative of the overall outbreak. They said that it is important to remain alert to the possibility of spread to other groups whilst still balancing targeted health promotion to groups disproportionately affected by the current outbreak.