Estimating the prevalence of Monkeypox among men who have sex with men in a major city in Southwest China, since 2023 via capture–recapture methods
摘要
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 nonendemic 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 still shows ongoing transmission, with the total number of reported cases in 2023 ranking tenth in the world. With the gradual increase in 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 constitute a high-risk group for mpox infection and are central to prevention and control efforts aimed at halting the spread of the virus.
ObjectiveThe 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 epidemiological situation of mpox infection and formulating prevention and control strategies.
MethodsA capture‒recapture method was applied to estimate the number of mpox cases in MSM populations residing in or active in Chengdu city beginning on 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.
ResultsThe first capture tagged 1501 individuals, 31 of whom were mpox cases, and the second capture recruited a total of 1538 individuals, 18 of whom were mpox cases. A total of 21 people were 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), the size of the MSM population in Chengdu city to be 105,070 (95% CI: 62,751–147,391) or 115,577 (95% CI:66,794–164,361), and the prevalence rate of mpox infection to be 2.88 per 1,000 (95% CI: 0.33–9.85 per 1,000) or 2.62 per 1,000 (95% CI: 0.29 − 9.25 per 1,000).
ConclusionThe 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 remains present among the MSM population in Chengdu, and behavioral interventions targeting this population are necessary to control the transmission of mpox.
Clinical trial numberNot applicable.