Artemisinin-based combination therapies (ACTs) are the main treatment for falciparum malaria in Africa. Artemisinin partial resistance (ART-R), characterized by delayed parasite clearance after treatment, has been confirmed in four sub-Saharan African countries. In Ethiopia, molecular surveys have detected the Pfkelch13 R622I mutation associated with ART-R at multiple sites, but no study has yet combined clinical, molecular, and in vitro evidence to confirm ART-R per WHO criteria. This multisite study conducted across five sentinel sites in Ethiopia (2024-2025) assessed day-3 parasite positivity after artemether-lumefantrine treatment, Pfkelch13 genotyping, and ring-stage survival assay on culture-adapted field isolates, to determine whether ART-R is confirmed in Ethiopian Plasmodium falciparum populations.

This study integrated three WHO-required lines of evidence to confirm artemisinin partial resistance (ART-R) in Ethiopia: (1) clinical evidence through day-3 parasite positivity assessment after artemether-lumefantrine treatment in therapeutic efficacy studies; (2) molecular evidence through Pfkelch13 propeller domain genotyping; and (3) phenotypic in vitro evidence through ring-stage survival assay (RSA0-3h) on culture-adapted field isolates. Five sentinel sites were selected across malaria-endemic regions of Ethiopia. Blood samples were collected at enrollment (day 0) and day 3. Isolates were cryopreserved and shipped to France (Strasbourg) for RSA.

Inclusion Criteria:

• Age ≥ 6 months
• Microscopically confirmed uncomplicated Plasmodium falciparum monoinfection
• Axillary temperature ≥ 37.5°C or history of fever in the past 24 hours
• Ability to take oral medication
• Written informed consent from patient or parent/guardian
• Residence in the study area with intention to remain during follow-up

Exclusion Criteria:

• Severe or complicated malaria (WHO criteria)
• Mixed Plasmodium infection
• Pregnancy or breastfeeding
• Known hypersensitivity to artemether-lumefantrine
• Antimalarial treatment in the 4 weeks prior to enrollment
• Severe malnutrition
• Concomitant febrile illness other than malaria requiring systemic treatment

Individual participant data (IPD) underlying the results reported in the published article will be made available upon reasonable request to the corresponding author, following publication. Data will include anonymized clinical outcome data, Pfkelch13 genotyping results, and ring-stage survival assay results.

Beginning 6 months after publication

Researchers who provide a methodologically sound proposal. Requests should be directed to the corresponding author. Data will be shared after signing a data access agreement.