High Brucellosis Prevalence and Risk Among School-Age Children in Kenyan Pastoral Health Facilities: A Facility-Based Surveillance Study

BackgroundBrucellosis remains endemic in pastoral sub-Saharan Africa, yet systematic surveillance data on human prevalence and risk factors in these communities are limited. We estimated brucellosis prevalence and identified associated risk factors among febrile patients in two Kenyan pastoralist health facilities. Methodology/Principal FindingsProspective facility-based surveillance was conducted between February 2023 and July 2024 at Laisamis Sub-County Referral Hospital (Marsabit County) and Mailwa Health Center (Kajiado County). Consecutive enrollment included patients [&ge;]1 year of age, with acute febrile illness and brucellosis-compatible symptoms. Venous blood samples underwent Rose Bengal Test (RBT) serology, real-time PCR for Brucella DNA, and indirect ELISA. Cases were defined using hierarchical laboratory criteria: RBT [&ge;]1:8, PCR positivity among low-titer RBT samples, or combined low-titer RBT and ELISA positivity. Modified Poisson regression with robust variance estimation identified factors independently associated with brucellosis. Among 441 enrolled participants, 67 (15.2%; 95% CI: 12.1%-18.8%) met brucellosis case criteria. Site-specific prevalence differed substantially: prevalence at Laisamis was 19.3% (95% CI: 15.4%-24.0%) compared to 3.5% at Mailwa (95% CI: 1.4%-8.6%; p<0.001). School-age children (5-14 years) experienced the highest age-specific prevalence at 31.0%, representing 38.8% of all cases despite comprising only 19.0% of the study population. In multivariable analysis, three factors remained independently associated with brucellosis: school-age group (5-14 years) compared to adults aged 15-49 years (adjusted prevalence ratio [aPR]: 2.42; 95% CI: 1.54-3.81; p<0.001), prolonged fever >7 days (aPR: 1.82; 95% CI: 1.19-2.77; p=0.005), and muscle pain (aPR: 2.44; 95% CI: 1.10-5.42; p=0.028). Sensitivity analysis restricting case classification to RBT [&ge;]1:8 or PCR positivity (excluding low-titer RBT with ELISA+ cases) yielded associations of similar direction and magnitude. Conclusions/SignificanceBrucellosis prevalence in Kenyan pastoral health facilities is high, with school-age children emerging as a previously underrecognized high-risk group. Geographic variation in burden appears to align with ecological differences in livestock management and mobility. These findings suggest the need for age-targeted prevention strategies and diagnostic screening for prolonged fever in children. Coordinated action between clinical and veterinary sectors, aligned with Kenyas national brucellosis control strategy, is needed to translate epidemiologic evidence into effective control efforts in pastoral communities. Author SummaryBrucellosis is a bacterial infection spread from livestock to people, common in communities that depend on animals for their livelihood. In Kenyas pastoral regions, families live in close contact with cattle, goats, sheep, and camels, regularly consuming fresh milk and assisting with animal births-activities that can transmit the disease. We tested 441 patients with fever at two health facilities in contrasting pastoral areas of Kenya and found that about 1 in 6 had brucellosis. The burden was not evenly distributed: one site had five times more cases than the other, likely reflecting differences in how livestock are managed and how much animals move and mix. Most unexpectedly, school-age children (5-14 years) had the highest rates of infection-nearly one in three tested positive-and accounted for almost 40% of all cases. These findings challenge the common assumption that brucellosis primarily affects adults through occupational exposure, and points to household milk-handling practices and childrens involvement in animal care as important but overlooked transmission routes. Patients with fever lasting more than a week were also at higher risk, suggesting that prolonged fever in children should prompt clinicians in pastoral areas to consider brucellosis. These findings highlight the need for prevention strategies that specifically address childrens exposures and for coordination between human health and veterinary services to reduce transmission at its source.