Epidemiological and Characterization of First Dengue Epidemic in Chad from August 2023 to January 2024: A Retrospective Study

Background: Dengue cases have risen dramatically in all six World Health Organization (WHO) regions, with the number of new cases virtually doubling each year. The first dengue outbreak in Chad occurred in the provinces of Ouaddaï, Wadi Fira, Sila, and Ndjamena from August 3, 2023 to January 7, 2024, following the displacement of refugees due to the Sudan conflicts into neighboring Chad. This study looked at the epidemiological data from Chad's dengue outbreak, including clinical features, laboratory and environmental studies, and confirmed dengue cases. It also looked into epidemic response and control strategy, as well as challenges faced during the outbreak response. Methods: We conducted a cross-sectional study using a retrospective review of records on suspected, probable, and confirmed dengue cases. A descriptive analysis was conducted on sociodemographic data, trends in dengue cases, clinical features, and case fatality. A logistic regression model was also developed to identify factors associated with confirmed dengue cases. Odd ratios and their (95% CI) were measured, and P-values ≤ 0.05 were considered statistically significant. We also measured the diagnostic tests to see how the reverse transcription polymerase chain reaction (RT-PCR)/Rapid testing performed in comparison to the case definition combined with the Dengue rapid test (RDT). Results: A total of 2,404 suspected dengue cases were registered, of which 63 were confirmed cases including 1 death, a case fatality rate of 1,59 %. Among all confirmed cases, 34/63 (54.0%) were men, 29/63(46.0%) were females, and 84.1% ranged in age from 15 to 54 years. The most common symptoms were fever (100%), headache (100%), myalgia (75%), and arthritis (75%). There was also a case of 0.01% of acute dengue fever and shock. Multivariable logistic analysis revealed that health centers were less likely to detect dengue cases than institutions cases (AOR: 0.04, 95%CI: 0.00-0.77, p-value = 0.033) compared to the community. When comparing the case definition combined with dengue RDT to RT-PCR a sensitivity of 100% (95%CI: 94.2%-100%), specificity of 93.2% (95%CI: 92.2%-94.2%), and PPV of 28.5% (95%CI: 23.0%-34.8%) were found. The circulating serotype for all the confirmed cases was DENV-1, genotype III. Conclusions: This study highlights the multifaceted challenges of dengue epidemiology in the context of Chad’s ongoing humanitarian crisis. The findings demonstrate that displacement and overcrowding in regions bordering conflict zones may have facilitated vector exposure and transmission. The low sensitivity of current diagnostic approaches further complicates timely detection and management. Strengthening dengue surveillance, enhancing diagnostic capacity, and implementing proactive vector control strategies during inter-epidemic periods are essential to prevent future outbreaks. These efforts must be integrated into broader public health preparedness and emergency response systems, particularly in vulnerable, crisis-affected settings.