Ongoing sporadic monkeypox cases: neutralising antibody detection in asymptomatic individuals

In their Correspondence, Silvia Accordini and colleagues¹ described the case of a 35-year-old man who used pre-exposure prophylaxis (PrEP) for HIV who, after a household contact with a person with mpox (formerly known as monkeypox), did not develop any skin lesion, but tested positive for MPXV and subsequently had seroconversion (indirect immunofluorescence) at 30 days follow-up.¹ To support the authors speculation, we present the case of a 35-year-old man who has sex with men who uses PrEP without a previous mpox or smallpox vaccination history, whose polyamorous partner was diagnosed with mpox.

The day after the diagnosis, while completely asymptomatic, our patient underwent a full physical examination that did not detect any sign of infection. The patient was told to seek medical attention at any sign or symptom of infection in the 21 days following the last contact with their partner and to refrain from sexual activity. After 4 days, the patient returned reporting pubic pustules in absence of any other symptom. The presence of MPXV DNA was investigated on pharynx and lesion swabs by RT-PCR test. He also underwent a full sexually transmitted infections screen and HSV-1/2 DNA on lesion sample. All tests came back negative with the exception of HSV-1 DNA on lesion swab and Neisseria gonorrhoeae on anal sample; the patient was thus prescribed with oral valacyclovir and ceftriaxone, and reported full healing of the lesions. The patient did not develop any other symptoms for the whole surveillance period. After 1 month, a serological test was proposed to look for neutralising antibodies against MPXV using the in vitro plaque reduction neutralisation test. A serum sample of the patient was diluted and mixed with MPXV suspension on Vero E6 cell culture. The test was positive for mpox-virus neutralising antibodies with a titre of 1:160.

Reda and colleagues² called for greater attention on infection control, including individuals who are asymptomatic and paucisymptomatic. Nevertheless, Van Dijck and colleagues³ underscored how unrecognised signs or unreported symptoms account for almost all the cases of what were believed to be asymptomatic infections.

Our experience, corroborated by an active surveillance and accurate physical examination, supports the findings by Accordini and colleagues¹ in reinforcing the speculations that, not only individuals with atypical presentations, but also people who are completely asymptomatic might have a role in spreading and sustaining MPXV circulation, justifying the persistent sporadic occurrence of mpox cases nowadays, in a phase of apparent remission of the mpox epidemic.

We declare no competing interests.