JMIR Publications

ABSTRACT

Background:

Monkeypox (mpox) is a zoonotic disease caused by the mpox virus, which was previously observed primarily in west-central Africa. Since May 2022, mpox outbreaks have emerged in several non-endemic countries around the world and have continued to spread, mainly through close contact (including sexual contact) in the population of men who have sex with men (MSM). Since June 2, 2023, when the first indigenous case of mpox in mainland China was reported in Beijing, the mpox epidemic in China has lasted for more than a year, and is still showing delayed transmission, with the total number of reported cases in 2023 ranking tenth in the world. With the gradual increase of the total number of indigenous cases, cases among females have been found to be infected via sexual contact, and there is a risk of further spread of the epidemic to the general population. MSM are a high-risk group for mpox infection and are central to prevention and control efforts aimed at halting the spread of the virus.

Objective:

The aim of this study is to ascertain the prevalence of mpox infection among MSM in Chengdu and to provide a scientific basis for predicting the mpox epidemiological situation and formulating prevention and control strategies.

Methods:

A capture-recapture method was applied to estimate the size of mpox cases in MSM populations residing or active in Chengdu City since May 1, 2023. The first capture and tagging were conducted at offline activity sites of the MSM population, and the second capture was carried out through peer network snowball sampling. Capture was accompanied by a questionnaire survey covering mpox diagnosis history, suspected mpox symptoms, risk exposure in the 21 days prior to symptom onset, and HIV and sexually transmitted infection (STI) status.

Results:

The first capture tagged 1501 individuals, of whom 31 were mpox cases, and the second capture recruited a total of 1538 individuals, of whom 18 were mpox cases. A total of 21 people had been tagged in the second capture, of whom 1 was a mpox case. The capture-recapture method estimated the number of mpox cases among MSM in a provincial capital city to be 303 (95% CI: 48~ 618 ), and the size of the MSM population in Chengdu city to be 105,070 (95% CI: 62,751 ~ 147,391), and the prevalence rate of mpox infection to be 2.88 per 1,000 (95% CI: 0.33 ~ 9.85 per 1,000).

Conclusions:

The capture-recapture method can estimate the size of the MSM population and the number of mpox cases, providing essential data for mpox prevention and control. Mpox infection among the MSM population in Chengdu is of notable proportion, and behavioral intervention targeting this population are necessary to control the transmission of mpox.