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

Background The sex distribution of newly diagnosed HIV patients shows substantial geographical heterogeneity worldwide. While more than 60% of new patients within sub-Saharan Africa are women and girls, men constitute the majority of notified patients elsewhere. In China, national surveillance data (2010–2022) reveal that males account for 78.84% of newly diagnosed HIV patients among adults aged ≥ 15 years, with a national male-to-female ratio of 3.64:1. Nevertheless, the predominance of male HIV patients is far greater among coastal cities in China with large migrant populations, such as Xiamen. Prior research has relied solely on isolated temporal or spatial modeling, with no mixed-methods evidence explaining the correlates of male-skewed HIV patient distributions. In this study, long-term temporal sex-ratio trends and static spatial clustering patterns in Xiamen’s HIV epidemic were quantified, and key correlates were extracted to guide localized preventive interventions. Methods We extracted verified Xiamen-specific HIV/AIDS surveillance records from 2003 to 2025 from the China National Disease Prevention and Control Information System. Quantitative analyses included descriptive epidemiological analysis, descriptive decomposition analysis comparing the ratio of male-to-female patients when men who have sex with men (MSM) patients were and were not excluded, exploratory Pearson correlation and univariate linear regression analyses (sensitivity analyses provided in the Supplementary Materials), chi-square tests, and spatial clustering analysis with global Moran’s I and LISA-based local Moran’s I statistics (local indicators of spatial association, LISA). Semistructured one-on-one interviews with 32 stakeholders provided qualitative evidence on reporting bias and screening inequities. All individual identifiers were permanently deidentified before analysis. Results We documented 4,326 HIV/AIDS cases (90.45% male, 9.55% female), yielding an overall sex ratio of 9.47:1, which peaked at 18.19:1 in 2017. After 2007, MSM became an important transmission route, accounting for 52.38% of all cumulative cases. Temporal decomposition compared male-to-female ratios with and without MSM patients: starting from an initial gap of only 2.00 in 2007, the gap between these two metrics widened to a peak of 11.63 in 2017 and fluctuated thereafter. After excluding MSM patients, the pooled 2007–2025 male-to-female patient ratio decreased substantially from 9.55:1 to 3.99:1. Significant spatial high–high hotspots of MSM were detected in central Siming and Huli Districts. Qualitative data confirmed that concealment of same-sex sexual behavior among MSM contributed to transmission misclassification, in addition to substantial increases in the number of MSM who were screened during the study period. Conclusions The cross-city inflow of migrant MSM represents an important observed correlate of extreme male-skewed HIV patient ratios in Xiamen, with secondary factors exaggerating the imbalance, including residual historical injection drug transmission effects, systematic undercounting of MSM cases driven by the concealment of same-sex sexual histories, and insufficient screening for high-risk female groups. These findings provide empirical evidence for other coastal cities in China with large migrant populations.