Extreme Male Skew in Xiamen’s Notified HIV Cases Linked to MSM Transmission and Migrant Inflow

Xiamen, a coastal city in southeastern China with a large migrant population, has recorded one of the most male-skewed HIV/AIDS epidemics documented in national surveillance data. A new analysis of verified city-level records from 2003 to 2025, drawn from the China National Disease Prevention and Control Information System, identified 4,326 notified HIV/AIDS cases, of which 90.45 percent were male and 9.55 percent female. That yields an overall male-to-female patient ratio of 9.47 to 1, a figure that climbed to a peak of 18.19 to 1 in 2017. For comparison, national surveillance data from 2010 to 2022 show that males accounted for 78.84 percent of newly diagnosed HIV patients aged 15 years or older across China, with a national male-to-female ratio of 3.64 to 1.

The study, published as an open-access research article in BMC Public Health, went beyond the isolated temporal or spatial modeling used in most previous work by combining quantitative surveillance analysis with semistructured one-on-one interviews involving 32 stakeholders. All individual identifiers were permanently deidentified before analysis. The mixed-methods design was intended to explain why the sex distribution of notified patients in Xiamen diverges so sharply from both the national picture and the global pattern, in which women and girls constitute more than 60 percent of new patients in sub-Saharan Africa while men predominate almost everywhere else.

A central quantitative finding concerns the role of men who have sex with men (MSM). After 2007, MSM emerged as an important transmission route in Xiamen, ultimately accounting for 52.38 percent of all cumulative cases in the dataset. To characterize the contribution of this route, the researchers performed a descriptive decomposition analysis, comparing the male-to-female patient ratio with and without MSM patients included. In 2007, the gap between these two metrics was only 2.00. It widened to a peak of 11.63 in 2017 and fluctuated in the years that followed, tracking the growing weight of MSM transmission in the city’s notified epidemic.

The effect of removing MSM cases from the calculation is substantial. When MSM patients were excluded, the pooled male-to-female ratio for 2007 to 2025 fell from 9.55 to 1 to 3.99 to 1, implying that roughly two-thirds of the observed male excess in notified patients over that period is statistically associated with the MSM transmission category. The residual imbalance, while much smaller, still exceeds the national ratio, suggesting that additional mechanisms contribute to the skew.

Spatial analysis added a geographic dimension to the picture. Using global Moran’s I statistics and local indicators of spatial association (LISA) based on local Moran’s I, the team detected statistically significant high–high clustering hotspots of MSM-associated cases in Xiamen’s central Siming and Huli Districts. This concentration in the city’s urban core is consistent with the study’s identification of cross-city inflow of migrant MSM as an important observed correlate of the extreme male-skewed patient ratios, a pattern the authors note is relevant to other coastal Chinese cities with large migrant populations.

The qualitative interviews shed light on why notified numbers may understate the true distribution of infections. Stakeholders reported that concealment of same-sex sexual behavior among MSM contributed to transmission misclassification, meaning some cases acquired through male-to-male sexual contact were recorded under other categories. This systematic undercounting of MSM cases exaggerates the apparent male skew in the notified data, because it shifts infections that would reinforce the MSM-associated imbalance into categories shared with female partners.

The interviews and analyses also pointed to screening inequities as a secondary factor. Insufficient screening for high-risk female groups means that infections among women are more likely to go undetected, deflating the female numerator in the sex ratio. The authors additionally cite residual historical effects of injection drug transmission as a contributing element to the imbalance. Together, these secondary factors compound, rather than create, the dominant MSM-associated pattern.

Methodologically, the study combined descriptive epidemiological analysis, the decomposition analysis, exploratory Pearson correlation and univariate linear regression analyses with sensitivity analyses provided in the supplementary materials, chi-square tests, and the spatial clustering statistics described above. The authors are careful to frame their findings as observed correlates rather than proven causal effects: the decomposition quantifies how much of the sex ratio is associated with MSM classification, and the interviews explain plausible reporting mechanisms, but the design does not establish causal pathways between migration, concealment, and individual infection risk.

The study’s conclusions carry practical weight for public health planning. By quantifying how much of Xiamen’s extreme sex imbalance is associated with a single transmission category, and by locating the clustering of MSM-associated cases in two central districts, the research offers an empirical basis for localized preventive interventions. The authors argue that the findings provide transferable evidence for other coastal cities in China with large migrant populations, where similar combinations of MSM transmission concentration, reporting concealment, and uneven screening coverage may be producing comparable distortions in notified HIV/AIDS statistics.

As with any surveillance-based analysis, the figures reflect notified patients rather than total infections, and the interview sample of 32 stakeholders, while sufficient to surface recurring themes about reporting bias and screening access, cannot be generalized statistically. The article was published under open access on 22 October 2026, with the version shared early for faster access and subject to further editorial edits before the final Version of Record replaces it. Even in this preliminary form, the scale of the discrepancy it documents, a citywide sex ratio roughly five times the national figure at its 2017 peak, marks Xiamen as an instructive case study in how transmission structure and detection patterns jointly shape the visible face of an HIV epidemic.

Subject of Research: Sex imbalance and spatial clustering of notified HIV/AIDS cases in Xiamen, China

Article Title: Severe sex imbalance among notified HIV/AIDS patients in Xiamen, China (2003–2025): temporal trends, spatial clustering and qualitative interviews of agglomeration correlates of men who have sex with men

Article References: Ma, G., Zhang, W., Ke, R., Deng, H., & Xue, J. (2026). Severe sex imbalance among notified HIV/AIDS patients in Xiamen, China (2003–2025): temporal trends, spatial clustering and qualitative interviews of agglomeration correlates of men who have sex with men. BMC Public Health. https://doi.org/10.1186/s12889-026-30051-2

Image Credits: AI Generated

DOI: 10.1186/s12889-026-30051-2

Keywords: HIV/AIDS, Xiamen, men who have sex with men, sex ratio, spatial clustering, surveillance data, migrant populations, BMC Public Health, epidemiology, transmission misclassification, screening inequity, China