Monkeypox Detected in Asymptomatic Men

Monkeypox virus was detected on the anal swabs of asymptomatic men who have sex with men (MSM) at a sexual health clinic in Paris, according to a retrospective study.

Among 213 MSM who had anal swabs collected for Chlamydia trachomatis and Neisseria gonorrhoeae, 200 underwent monkeypox-specific PCR testing and 6.5% were positive for the virus, reported Charlotte Charpentier, PharmD, PhD, of Hôpital Bichat-Claude Bernard in Paris, and colleagues.

“Whether this indicates viral shedding that can lead to transmission is unknown. If so, the practice of ring postexposure vaccination around symptomatic persons with probable or confirmed monkeypox virus infection may not be sufficient to contain spread,” they wrote in the Annals of Internal Medicine.

All 13 affected men were advised to limit sexual activity for 21 days and to notify recent sexual partners. While none of the men initially reported symptoms, two subsequently presented with symptoms at the health clinic — one with anal rash and the other with pharyngitis and fever but no anal symptoms.

Of the remaining 187 men who initially tested negative, three presented to the clinic with symptoms over 3 weeks later and tested positive.

These findings are in line with a recent study that reported that two asymptomatic patients were found to be infected with the monkeypox virus.

“Although it is not yet clear whether the positive PCR result represents the presence of infectious virus, it will not be surprising if it is present because the possibility of asymptomatic infections is not a new finding,” wrote Stuart N. Isaacs, MD, of the Perelman School of Medicine at the University of Pennsylvania in Philadelphia, in an accompanying editorial.

“However, it raises the question of whether asymptomatic or subclinical infections are contributing to the current worldwide outbreak,” he added.

France has issued an advisory for all MSM with multiple partners to be vaccinated.

Historically, it has been thought that the risk of transmission of monkeypox and variola virus is highest with the presence of a rash, Isaacs noted. In fact, “the presence of virus in throat cultures in asymptomatic people was believed to be of little or no epidemiologic importance given that the successful eradication of smallpox was due in part to the ability to always identify a source patient. However, the current worldwide monkeypox epidemic and the mode of human-to-human transmission may provide evidence that asymptomatic or preclinical spread can occur.”

For this study, Charpentier and colleagues included 213 MSM who visited the Paris clinic from June 5 to July 11 for routine sexually transmitted infection testing. Median age was 38, and 52% were living with HIV and receiving antiretroviral therapy, with a median of 9 years since diagnosis.

Of the 13 men who tested positive for monkeypox, eight were living with HIV. All had undetectable HIV-1 viral load, and all had a CD4 T-cell count above 0.500 × 10⁹ cells/L, except one who had a count of 0.123 × 10⁹ cells/L.