Epidemiological trends and pertussis-related mortality in Jigawa State, Northwest Nigeria: evidence from five years of case-based surveillance

Abstract

To describe five-year epidemiological trends of pertussis in Jigawa State, northwest Nigeria, using case-based surveillance data. A retrospective descriptive cross-sectional analysis was conducted on 768 pertussis cases reported through the Integrated Disease Surveillance and Response (IDSR) system between 2019 and 2023. The primary outcome variable was patient survival status (alive or died). Data were analyzed using SPSS version 22, with statistical significance set at 5%. A total of 768 pertussis cases met the inclusion criteria, with ages ranging from 8 to 180 months (median: 60 months; IQR: 36–84). Cases were reported between epidemiological weeks 2 and 39 (median: week 13; IQR: 2–39), with 51.6% occurring during weeks 1–13. Cases were reported from 14 of 27 LGAs, with Auyo LGA accounting for the largest proportion (18.7%). The overall case-fatality rate was 7.3%, with the highest mortality among children aged 5–9 years (8.5%), and followed by under-five children (7.1%). All pertussis-related mortalities 16.9% were recorded in 2023 outbreak. Attack rates increased over time, particularly 2022. In 2019, rates were 5.0 per 100,000 among both under-five and 5–9-year-old children, compared with 0.6 per 100,000 among adolescents. In 2020, rates declined to 2.0 per 100,000 in both child groups. In 2021, children aged 5–9 years had the highest rate (2.1 per 100,000). Rates increased markedly in 2022 to 7.4 per 100,000 among under-five children and 6.3 per 100,000 among those aged 5–9 years, while adolescents recorded 0.3 per 100,000. In 2023, rates further increased to 10.2, 8.8, and 5.1 per 100,000 among under-five children, 5–9-year-olds, and adolescents, respectively. Mortality was significantly higher in the Northeast Senatorial Zone (14.4%; p < 0.001), during the 2023 outbreak (16.9%; p < 0.001), and among vaccinated individuals (15.4%; p < 0.001). In adjusted analysis, outbreak timing, vaccination status, and hospital admission independently predicted mortality. Compared with outbreaks occurring during weeks ≥ 26, those during weeks 1–13 and 14–25 had 95% and 90% lower odds of mortality, respectively (aOR = 0.05; 95% CI: 0.02–0.10 and aOR = 0.10; 95% CI: 0.03–0.20). Unvaccinated cases had 80% lower odds of mortality than vaccinated cases (aOR = 0.20; 95% CI: 0.10–0.30), whereas admitted cases had approximately 10-fold higher odds of mortality (aOR = 10.2; 95% CI: 5.7–18.2). Pertussis is re-emerging in Jigawa State with substantial morbidity and mortality. High mortality among hospitalized and delay in presenting cases highlights the need to strengthen surveillance, ensure earlier case detection, improve clinical management, and enhance routine immunization coverage. Sero-prevalence studies are needed to assess immunity gaps, particularly among older age groups contributing to ongoing transmission. Not applicable