Municipality size and epidemiological characteristics among confirmed mpox cases in Spain

In 2022, a multistate mpox outbreak represented a new global health challenge and highlighted sexual contact as the main route of transmission. Spain reported the highest number of cases in Europe but showed an irregular distribution of cases across its territory. This study aims to describe the characteristics of mpox cases among individuals living in large cities versus smaller municipalities, and to examine whether municipality size is associated with mpox incidence and with epidemiological and clinical characteristics among confirmed cases. This is a cross‑sectional study of mpox cases in men aged ≥ 16 years confirmed between June 2022 and January 2023 in seven Spanish regions. Epidemiological and clinical variables were analysed in large cities (population ≥ 200 000) and smaller municipalities. Descriptive analyses were performed. Odds ratios (aOR) with 95% confidence intervals (CI95%) were obtained through logistic regression models to describe characteristics of mpox cases among individuals. To assess differences in cumulative incidence according to municipality size, cumulative incidence ratios (aCIR CI95%) were obtained through Poisson regression models with robust variance. Among the 1,162 reported mpox cases, 776 (66.8%) were from large urban areas. Among mpox cases, living in large cities was significantly associated with being born in low-income countries (aOR = 2.1, 1.2–3.5), having a previous sexually transmitted infection (STI) (aOR = 1.6, 1.1–2.3), participating in chemsex (aOR = 1.7, 1.0–2.7), having sex in private leisure venues (aOR = 1.5, 1.1–2.2), using pre-exposure prophylaxis (PrEP) (aOR = 1.7, 1.1–2.5), and regularly using condoms during casual sex (aOR = 1.9, 1.3–2.9). Clinical complications were less frequent in large cities (aOR = 0.4, 0.2–0.7). Living in a large city was associated with a higher cumulative incidence of mpox (aCIR = 2.7; 1.9–3.7) compared with living in smaller municipalities. Living in a large city was associated with a higher cumulative incidence of mpox. It was also associated with characteristics linked to chemsex practices, sexual encounters in private leisure venues and previous STI diagnosis. These findings support considering municipality size and urban social dynamics when planning public health responses to mpox.