An in-depth comparison: first wave of mpox in Rio de Janeiro, Brazil and Lisbon, Portugal

The 2022 mpox outbreak spread rapidly beyond endemic regions, affecting multiple countries with broadly similar transmission patterns but different public health responses and surveillance systems. We compared laboratory-confirmed mpox infections reported during the first epidemic wave in Rio de Janeiro, Brazil, and Lisbon, Portugal, with particular attention to demographic characteristics, clinical presentation, transmission patterns, hospitalization, and the role of HIV status.

We conducted a retrospective analysis of routinely collected, deidentified surveillance data from national notification systems in Brazil and Portugal. Adults with laboratory-confirmed mpox reported between May and December 2022 were included. Variables were harmonized across datasets, and missing data were retained without imputation. Descriptive analyses were performed by city and HIV status. Group comparisons used Pearson's chi-square test, Fisher's exact test, Mann-Whitney U test, and two proportion Z tests, as appropriate. Data completeness was also explored.

A total of 1,614 individuals were included: 960 from Rio de Janeiro and 654 from Lisbon. Mean age was similar in both cities (34.5 vs 34.9 years), but Lisbon had a higher proportion of males (99.4% vs 93.0%). The epidemic curves showed a similar rise-and-decline pattern, with an earlier peak in Lisbon (June 2022) and a later peak in Rio de Janeiro (August 2022). Skin or mucosal lesions were the most frequently reported manifestation in both settings, affecting more than 85% of individuals. Fever was reported more often in Rio de Janeiro, whereas adenopathy and asthenia were more commonly recorded in Lisbon. Within each city, symptom profiles were not significantly different between people living with HIV and those not living with HIV. Hospitalization rates were low overall in both cities (5.7% in Rio de Janeiro and 5.4% in Lisbon), although people living with HIV in Rio de Janeiro had higher odds of hospitalization than those without HIV. Data completeness was generally better in Rio de Janeiro than in Lisbon.

Rio de Janeiro and Lisbon experienced similarly shaped first wave mpox epidemics, despite differences in timing, surveillance completeness, and health system context. HIV status did not appear to meaningfully modify acute clinical presentation, while hospitalization risk may have been influenced by differences in immune status and care pathways. These findings highlight the importance of harmonized, high-quality surveillance to support more accurate cross-country comparisons and better targeted public health responses.