Evaluating LLM Robustness Under Domain-Specific Prompt Perturbations in Public Health Applications

Abstract

Large language models (LLMs) are increasingly applied in public health applications, yet their robustness to non-clinical user inputs remains underexplored. We propose a domain specific robustness benchmark that evaluates LLMs under two perturbation types that commonly arise when non-clinical users interact with health AI systems: misinformation framing (MF), where prompt might be injected by false health claims, and layperson rewriting (LR), where patients describe symptoms in everyday language rather than medical terminology. Our goal is to evaluate the stability of LLMs under these perturbation. Experiments show that MF degrades accuracy by 7.2 pp on average with prediction flip rates of 9-38 percent, even when claims are explicitly labelled as unsupported; LR causes only 1.4 pp degradation. These findings highlight two distinct deployment risks in public health settings: models may produce incorrect outputs when users unintentionally carry misinformation into their queries, and may misinterpret clinically relevant details when patients use informal language. Both risks call for perturbation-aware robustness evaluation beyond clean baseline benchmark