Real-time sentinel syndromic surveillance for infectious disease detection: lessons from the 4S network in Senegal, 2015–2023

Background Sub-Saharan Africa faces persistent challenges in the timely detection of infectious disease outbreaks due to inadequate early warning and response systems. To address this gap, Senegal's Ministry of Health partnered with the Institut Pasteur de Dakar to establish the Senegalese Syndromic Sentinel Surveillance Network (4S Network) in 2012 a comprehensive surveillance system designed to identify epidemic-prone syndromes and enable rapid public health interventions. Methods We analysed data from the Senegalese 4S real-time sentinel syndromic surveillance network collected between 2015 (15 sites) and 2023 (27 sites). The network monitored four key febrile syndromes, including malaria, dengue-like syndromes, diarrheal syndrome, and influenza-like illness (ILI), via standardized WHO case definitions. Laboratory confirmation was achieved through molecular and serological testing of biological samples. Sentinel general practitioners submitted daily reports via a digital platform that facilitated real-time reporting and automated alert generation. We evaluated system performance through completeness, timeliness, temporal patterns, geographical distribution, and alert validation rates. Results During the nine-year surveillance period, the network documented 1,816,340 outpatient consultations, with febrile syndromes accounting for 11.7% of all visits and demonstrating notable annual fluctuations. Distinct regional patterns of infectious disease events were observed: ILI predominated in western regions, dengue-like syndromes were clustered in north-central areas, and malaria cases were concentrated in southeastern zones. The system demonstrated robust performance metrics, achieving 94.5% data completeness and 80.0% reporting timeliness. Of the 202 alerts generated, 51.0% received laboratory confirmation. Dengue virus circulation was documented in 2017, 2018, 2021, 2022, and 2023. Despite these successes, 37.1% of febrile cases remained etiologically unclassified. The system's early multidisciplinary investigation capabilities enabled swift outbreak containment and transmission control. Conclusion The 4S network validates the effectiveness and practical implementation of digital, real-time syndromic surveillance in Senegal. It successfully facilitated early outbreak detection and supported prompt public health responses. Although the system has significant potential for resource-constrained environments, addressing current operational limitations remains crucial for maximizing public health impacts. These findings provide strong evidence supporting the regional expansion of similar surveillance frameworks to enhance health security and epidemic preparedness throughout West Africa.