Mapping priority areas for measles surveillance: stratifying reintroduction and transmission risk in Rio de Janeiro, Brazil.

Objective: To stratify areas at risk of measles transmission in the state of Rio de Janeiro, using the risk assessment tool developed by the World Health Organization and Centers for Disease Control and Prevention, with adaptations to the regional context.

Methods: This ecological study used municipalities of Rio de Janeiro state as the units of analysis. The overall risk of measles transmission was evaluated based on the scores of indicators grouped into four categories: vaccination, threat assessment, quality of health care services, and living conditions. After summing and normalizing the scores for each category, weights were assigned to obtain the risk index. The 20%, 60%, and 90% centiles were used to establish cut-off points, classifying municipalities as low risk, medium risk, high risk, and very high risk. To evaluate the performance of the measles transmission risk index, a spatial overlay was performed with the cases reported in the epidemic period 2018-2020.

Results: A progressive increase in incidence rates of measles cases was observed across municipalities, corresponding to escalating transmission risk in different strata. About 97% of measles cases occurred in municipalities classified as high or very high risk, primarily located in the state's metropolitan region.

Conclusion: Given the potential risk of measles transmission during the post-elimination period, our findings reinforce the importance of developing and implementing tools to identify priority areas for surveillance. The spatial overlay indicated the method's effectiveness in identifying vulnerabilities associated with transmission other than low vaccine coverage, such as precarious living conditions and poor quality of health care services.