Public health surveillance systems are crucial for monitoring disease prevalence and health outcomes in South Africa. However, their effectiveness can be challenging to assess due to potential confounding factors. We employed a DiD regression analysis, accounting for temporal trends and geographical variations. The study utilised anonymized electronic health records from two provinces as our primary data source. Our findings indicate that the surveillance system in Province A showed a significant reduction of 15% in hospital admissions for respiratory infections compared to Province B over a five-year period. The DiD model provided robust evidence on the impact of public health interventions. Our study supports the use of this methodological approach for future evaluations. Future research should consider expanding the analysis to include more provinces and longer time periods to strengthen the findings' generalizability. public health surveillance, difference-in-differences, clinical outcomes, South Africa Treatment effect was estimated with $\text{logit}(p_i)=\beta_0+\beta^\top X_i$, and uncertainty reported using confidence-interval based inference.