Impact of the COVID-19 Pandemic on Human Brucellosis in Saudi Arabia: A Population-based Interrupted Time-series Study, 2014–2024

Human brucellosis remains an endemic zoonotic disease in Saudi Arabia (SA), characterized by marked regional heterogeneity and seasonal variation. The COVID-19 pandemic led to significant declines in reported infectious diseases, raising questions about whether these reductions reflect true decreases in transmission or disruptions in surveillance. The pandemic serves as a natural experiment to evaluate the resilience of infectious disease surveillance systems under stress. This study examines the impact of COVID-19 on human brucellosis incidence and assesses surveillance resilience in SA. A retrospective interrupted time-series analysis was performed using national surveillance data from the Saudi Ministry of Health from 2014 to 2024. The study was divided into three phases: Baseline (2014–2019), Disruption (2020–2021), and Recovery (2022–2024). Monthly case counts were analyzed using a negative binomial regression model to estimate changes in incidence levels and pandemic trends, accounting for overdispersion and seasonal variation. During the Baseline phase, reported human brucellosis incidence showed a significant upward trend (IRR = 1.008 per month, p = 0.001). In the Disruption phase, there was a sharp decline of about 55% in reported cases (IRR = 0.452, p < 0.001), with no significant change in slope ( p = 0.139), leaving incidence 22.6% below expected levels (IRR = 0.774, p < 0.001). In the Recovery phase, incidence gradually increased (IRR = 1.013 per month, p = 0.059) but remained 25.6% below expected levels (IRR = 0.744, p < 0.001), indicating incomplete recovery. Regional differences in recovery patterns were notable, with some areas showing significant increases while others remained stable. A consistent seasonal pattern was observed across all phases ( p < 0.05). Reported human brucellosis declined markedly during the COVID-19 disruption and remained below the counterfactual projection during recovery. These patterns are compatible with pandemic-related changes in case detection, healthcare access, reporting, exposure, or a combination of these mechanisms; the aggregated surveillance data cannot distinguish their relative contributions. Regional differences indicate heterogeneous post-pandemic reporting trajectories. The findings support strengthening surveillance resilience and integrated One Health coordination, including collaboration with national public health authorities such as the National Centre for Disease Prevention and Control (Weqaya).