Monkeypox Virus Shows Potential for Asymptomatic Transmission

Researcher holding blood test tube infected with monkey pox virus (MPXV). Doctor with a blood sample in a tube diagnosed with Monkeypox (MPXV) disease
Researchers evaluated anorectal specimens obtained from patients with asymptomatic monkeypox infection.

Anorectal specimens obtained from asymptomatic men who have sex with men (MSM) were found to test positive for monkeypox infection, suggesting the potential for asymptomic transmission of the infection, according to findings of a letter published in the Annals of Internal Medicine.

Anorectal specimens obtained from MSM (N=706) for routine screening for bacterial sexually transmitted infections (STIs) at the Hôpital Bichat-Claude Bernard in France were retrospectively evaluated for evidence of monkeypox infection between June and July 2022. All patients were either HIV-positive or receiving HIV pre-exposure prophylaxis.

A total of 383 patients were found to have symptoms suggestive of monkeypox infection, of whom 40% had anal lesions. Of these patients, subsequent polymerase chain reaction (PCR) testing confirmed monkeypox in 271 (71%). Among asymptomatic patients (n=323), 9.9% tested positive for Chlamydia trachomatis, 7.4% were positive for Neisseria gonorrhoeae, and 2.5% were positive for C trachomatis and N gonorrhoeae coinfection.

Of 213 patients who showed no evidence of either monkeypox or a STI, the median age was 38 (IQR, 29-48) years, and 52% had HIV infection for a median of 9 (IQR, 4-18) years and were receiving antiretroviral therapy.

Among the 213 patients with no evidence of a STI or symptoms suggestive of monkeypox infection, anorectal specimens were obtained from 200 for PCR testing. Results were positive for monkeypox infection in 13 (6.5%) of these patients. Of these patients, 8 had HIV infection.

The 13 asymptomatic patients with PCR-confirmed infection were advised to avoid sexual contact for 21 days, however, 2 of them subsequently developed symptoms suggestive of infection.

Of 187 patients who initially tested negative for monkeypox infection, 3 developed symptoms more than 3 weeks later and tested positive for the infection.

It is unknown whether these findings indicate “viral shedding that can lead to transmission,” study authors noted. “If so, the practice of ring postexposure vaccination around symptomatic persons with probable or confirmed [monkeypox] infection may not be sufficient to contain spread,” they concluded.

Disclosure: Multiple authors declared affiliations with industry. Please refer to the original article for a full list of disclosures.


Ferré VM, Bachelard A, Zaidi M, et al. Detection of monkeypox virus in anorectal swabs from asymptomatic men who have sex with men in a sexually transmitted infection screening program in paris, France. Ann Intern Med. Published online August 16, 2022. doi:10.7326/M22-2183