Mpox-HIV co-infection in a low-incidence setting: epidemiological insights from Qinghai, China.

Objective: Using the first reported case of mpox and HIV co-infection in Qinghai Province, China, as a case study, this paper examines the epidemiological characteristics and transmission dynamics of mpox-HIV co-infection in low-incidence settings, as well as systemic gaps in surveillance, diagnosis, and response. It aims to generate broadly applicable insights for mpox prevention and control in similar low-incidence regions worldwide. Methods: A retrospective epidemiological investigation was conducted involving Case A, a patient with mpox-HIV co-infection reported by a hospital in Qinghai Province on 24 June 2025, and the patient's close contacts. Case and close-contact definitions were applied in accordance with World Health Organization (WHO) criteria, the Results: Case A was a male patient living with HIV who reported sex with men. He first developed perineal pruritus on 19 June. The following day, his temperature rose to 39.4 °C, and his symptoms did not improve after medication. He sought medical attention at a hospital on 23 June and was discharged on 7 July after full recovery; the total duration of illness was 18 days. During the 21 days before symptom onset, the patient had no history of international or out-of-city travel, no history of smallpox vaccination, and no history of contact with wild animals. He had, however, recently experienced high-risk exposure within the men who have sex with men (MSM) community. On 24 June, the admitting hospital collected a nasopharyngeal swab specimen for mpox virus (MPXV) nucleic acid testing, which confirmed a diagnosis of mpox. On 27 June, genetic sequencing was performed on a venous blood specimen from the patient, and the virus was identified as MPXV clade IIb. The sequence was further assigned to the C.1.1 sublineage, full designation B.1.3.1.1, within MPXV clade IIb, formerly known as the West African clade. A total of three close contacts were identified, all of whom tested negative for MPXV nucleic acid. One close contact tested positive for MPXV IgG antibodies, suggesting previous exposure to MPXV. Taken together, the epidemiological history, serological findings, and timing of symptom onset suggest that high-risk sexual contact was the most likely route of exposure for Case A. The onset of symptoms was consistent with the typical mpox incubation period of 7-14 days after the reported high-risk sexual exposure. Phylogenetic analysis showed that the sequence most closely related to that from Case A was EPI_ISL_19893388, submitted by Taiwan, China. Previously reported cases in Qinghai Province were predominantly imported. However, Case A had no clear history of international travel or travel outside the province and therefore did not meet the typical epidemiological profile of an imported case. The transmission pattern was therefore more consistent with local transmission within specific social or sexual networks. This finding suggests that silent transmission may already be occurring in low-incidence regions. Discussion: Through a retrospective analysis of the first reported case of mpox-HIV co-infection in Qinghai Province, this study identified three key findings. First, the findings provide evidence of previously unrecognized exposure and possible silent transmission in a low-incidence region. These results may inform the early identification of hidden community transmission and the strengthening of early warning systems. The mpox virus sequence most closely related to that from Case A had been submitted from Taiwan, China. None of the three identified close contacts presented with typical clinical symptoms, such as fever or rash; however, one tested positive for MPXV IgG antibodies. Because all close contacts had high-risk exposure to Case A, this finding suggests the possibility of prior, unrecognized exposure within the local high-risk population network associated with the case. However, serological evidence alone cannot establish the exact source, timing, or direction of transmission. Second, this study shows that mpox surveillance in low-incidence areas relies primarily on passive reporting by healthcare institutions and lacks active screening mechanisms for high-risk populations. The effectiveness of passive reporting depends directly on individuals' willingness to seek medical care and their ability to recognize symptoms. Case A sought medical attention and was diagnosed only after the onset of a typical rash; earlier symptoms, such as fever and fatigue, did not receive sufficient attention, and the patient did not seek timely care. This suggests that individuals with mild, atypical, or asymptomatic infections may be missed by surveillance systems if they do not proactively seek medical attention. These findings provide evidence to support the optimization of active surveillance models in low-incidence areas and the transition from passive surveillance to more proactive prevention and control strategies. Third, this study highlights an important serological gap in mpox epidemiology and emphasizes the value of serological testing in identifying previous exposure and reconstructing possible transmission chains. Some infected individuals may not present with a typical rash or may have only mild symptoms. Moreover, after viral nucleic acid becomes undetectable, IgM and IgG antibodies may persist for an extended period. Serological markers can therefore help identify previous exposure, asymptomatic infection, and silent transmission, thereby addressing surveillance blind spots associated with reliance on case reports and nucleic acid testing alone. In summary, mpox prevention and control in low-incidence areas should priorities the risk of silent transmission. This requires strengthening proactive screening among high-risk groups, reducing over-reliance on healthcare-seeking behavior, and establishing dynamic serological surveillance systems to improve the early identification and control of silent transmission.