Antibiotic Prophylaxis Stewardship by Dental Hygienists and Infective Endocarditis Risk in South African High-Risk Patients: A Regression-Discontinuity Analysis of Prescribing Thresholds

South African dental hygienists prescribe antibiotic prophylaxis for infective endocarditis (IE) under a threshold rule that ties eligibility to cardiac lesion severity, yet the behavioural consequences of that threshold for stewardship have not been quantified. The design uses the DHS Program indicator 'Children with symptoms of ARI who received antibiotics' (CH_ARIS_C_ABI) as a calibration series for background antibiotic consumption, drawing on 164 country-survey observations from 33 African countries between 2002 and 2025 (mean 39.064, SD 15.715). The proposed analysis would estimate a local average treatment effect at the threshold, with dental hygienists as the unit of prescribing and IE hospitalisations as the downstream outcome. The threshold creates a stewardship gradient: hygienists just above the cutoff face a binary decision that encourages over-prescription, while those just below face a binary decision that encourages under-prescription, and the net effect on IE risk is ambiguous without local estimation. The contribution is a methodological framework for evaluating threshold-based prophylaxis policy in resource-constrained dental settings, together with a calibration strategy that uses existing DHS antibiotic data to bound background consumption. The framework is intended for prospective application where linked prescribing and IE surveillance data become available.