Association between Plasmodium falciparum Kelch13 mutations and malaria parasite clearance half-life after artemisinin-based therapy: an updated WWARN systematic review and individual patient data meta-analysis

Background: Artemisinin-based combination therapies remain the first-line treatment for uncomplicated Plasmodium falciparum malaria. Plasmodium falciparum Kelch13 mutations emerge and spread within distinct malaria epidemiological and immunological contexts, shaping the expression of artemisinin resistance (ART-R). Understanding the clinical phenotypes of these mutations requires evaluation across diverse transmission settings and geographic regions. Methods: A systematic review (SR) and individual patient data meta-analysis (IPDMA) were conducted (PROSPERO: CRD42019133366) to identify studies that included serial parasite density measurements and Kelch13 genotyping. Associations between Kelch13 mutations and parasite clearance half-lives (PC1/2) and Day 3 parasite positivity were assessed. Receiver operating characteristic (ROC) analyses identified PC1/2 thresholds most strongly associated with relevant Kelch13 mutations. Findings: The SR identified 86 eligible studies, and individual patient data were obtained from 45 studies (n=16,823 patients from 539 study sites in 33 countries). After excluding hyperparasitaemia, Day 3 parasite positivity exceeded 10% overall across all WHO-validated, candidate, and potential mutations, but not for other Kelch13 mutations. Parasite clearance rates were consistently shorter in moderate-to-high-transmission than in lower-transmission areas. The WHO threshold PC1/2>5h had a sensitivity of 36% (27.9-44.6) for detecting WHO-validated mutations in moderate-to-high transmission areas and 81% (78.5-82.8) in lower transmission areas. In moderate-to-high transmission settings, a PC1/2 threshold of 3.1h optimally discriminated WHO-validated mutations (ROC AUC 0.78; 95% CI 0.74-0.82; sensitivity 75% (95% CI:67%-82%); specificity 71%, 95% CI: 69%-73%). Additional emerging Kelch13 mutations associated with delayed parasite clearance were identified in relatively small African and Asian sample sets. Interpretation: Compared with WT parasites, parasites carrying WHO-validated ART-R mutations were associated with a 34%- 59% longer mean PC1/2, regardless of endemicity, treatment regimen, or age. Given the low sensitivity of the PC1/2>5h threshold for identifying WHO-validated ART-R parasites in moderate-to-high transmission settings, where its recalibration is indicated. Broader genotyping is warranted for identifying emerging Kelch13 mutations associated with delayed parasite clearance.