Mapping Geographical Patterns and High Rate Areas for Sexually Transmitted Infections in Portugal: A Retrospective Study Based on the National Epidemiological Surveillance System

Objective Monitoring disease variation using finer scales to identify high-rate communities is a critical aspect for precision public health and for efficient resource allocation. This study aimed to map the spatial patterns of chlamydia, gonorrhea, and syphilis; identify high-rate areas across Portuguese municipalities; and determine the association of these sexually transmitted infections (STIs) with socioeconomic deprivation, urbanicity level, and population density. Methods The STI notifications at municipality level for the period 2015 to 2017 were obtained from Portugal's Epidemiologic Surveillance System (Sistema Nacional de Vigilancia Epidemiologica). Spatial Bayesian models were used to calculate smoothed standardized notification rates, identify high- and low-rate areas and estimate associations (relative risk [RR], 95% credible intervals [95%CrI]). Results There were 4819 cases of chlamydia, gonorrhea, and syphilis reported, accounting for 15.3%, 33.2%, and 51.5% of the notifications, respectively. The STI notification rates were substantially higher in Porto and Lisbon Metropolitan Areas and concentrically disperse around those. Notification rates of the 3 STIs were strongly correlated (r > 0.8). Rates of gonorrhea (Q1-lowest density vs. Q5-highest RR, 2.10; 95% CrI, 1.08-4.25) and syphilis (RR, 3.16; 95% CrI, 2.00-5.13) were associated with population density. Notifications of chlamydia (Q1-least urban vs. Q5-most RR, 9.64; 95% CrI, 1.73-93.59) and syphilis (RR, 1.92; 95% CrI, 1.30-2.88) increased with urbanicity level. We also found that notification rates of gonorrhea were associated with socioeconomic deprivation (Q1-least vs. Q5-most deprived RR, 1.75; 95% CrI, 1.07-2.88). Conclusions Wide spatial inequalities in STI notification rates were observed, which were predominantly concentrated in the 2 metropolitan areas of the country. Our findings can help guide more targeted interventions to reduce STIs incidence.