SPICE-GRADE: Simultaneous Processing of Indirect Causal Evidence in Complex Pathways Using GRADE -An Exploratory Case Study

Background and Objectives Genetic mutations often result in antimicrobial resistance. Early identification of emerging resistance due to genetic mutations often relies on multiple coexisting pathways of indirect evidence. The GRADE approach, widely used to rate certainty in treatment comparisons, offers little guidance to address such situations. Motivated by the possibility of emerging resistance to malaria, we provide an example of how GRADE guidance might be adapted to address multiple pathways of indirect evidence, an approach we term SPICE-GRADE. We developed and here illustrate a structured approach for integrating direct and indirect causal evidence within GRADE, using antimalarial drug resistance mediated by Plasmodium falciparum Kelch13 (K13) mutations as a case study. Methods Confronted by the problem of applying GRADE to the question of emerging antimicrobial resistance to malaria, we simultaneously considered low-certainty direct evidence and two pathways of indirect evidence addressing a possible causal relation between K13 mutations and malaria recrudescence. Links between K13 mutations and ring-stage survival and between K13 mutations and delayed parasite clearance constitute the two indirect pathways. We addressed each link was independent, and for the two indirect links the extent of indirectness informed the final judgment. Results All 3 links relied on observational studies and therefore started as low-certainty evidence. For both, the direct link between K13 mutations and recrudescence, and the indirect link between K13 mutations and ring-stage survival, we rated the certainty up 2 levels for a very strong association, and then down 2 levels due to imprecision from small sample size in the direct link, and due to very serious indirectness in the indirect link. The third link, between K13 mutations and delayed parasite clearance, was rated up 1 level for a strong association and down one for serious indirectness. Although each link remained at low certainty, the consistent direction of effect and coherence across all links strengthened the overall causal inference. Situating the entire body of evidence on a continuum allowed us to rate the overall certainty toward the higher end of low certainty, providing a more robust conclusion than relying on direct evidence alone. Conclusion In this case study, we illustrate SPICE-GRADE as a structured way of mapping and assessing multiple causal links within the GRADE framework. Establishing SPICE-GRADE as a robust methodology for GRADE assessment will require formal methodological development with application across multiple contexts.