Variation in Calculating and Reporting Antimalarial Efficacy against Plasmodium falciparum in Sub-Saharan Africa: A Systematic Review of Published Reports

Abstract

Antimalarials, in particular artemisinin-based combination therapies (ACTs), are critical tools in reducing the global burden of malaria, which is concentrated in sub-Saharan Africa. Performing and reporting antimalarial efficacy studies in a transparent and standardized fashion permit comparison of efficacy outcomes across countries and time periods. This systematic review summarizes study compliance with WHO laboratory and reporting guidance pertaining to antimalarial therapeutic efficacy studies and evaluates how well studies from sub-Saharan Africa adhered to these guidelines. We included all published studies (January 2020 or before) performed in sub-Saharan Africa where ACT efficacy for treatment of uncomplicated Plasmodium falciparum infection was reported. The primary outcome was a composite indicator for study methodology consistent with WHO guidelines for statistical analysis of corrected efficacy, defined as an article presenting a Kaplan-Meier survival analysis of corrected efficacy or reporting a per-protocol analysis where new infections were excluded from the numerator and denominator. Of 581 articles screened, we identified 279 for the review. Molecular correction was used in 83% (232/279) to distinguish new infections from recrudescences in subjects experiencing recurrent parasitemia. Only 45% (99/221) of articles with therapeutic efficacy as a primary outcome and performing molecular correction reported corrected efficacy outcomes calculated in a way consistent with WHO recommendations. These results indicate a widespread lack of compliance with WHO-recommended methods of analysis, which may result in biases in how antimalarial effectiveness is being measured and reported from sub-Saharan Africa.

Figure 1.

Examples of msp1, msp2, and glurp electrophoretic band data from six pairs of day zero (D0) and day of failure (DX) samples. For clonal, single-strain infections, analysis is straightforward (participant 001 and 006). Analysis of multi-strain infections is more complicated and governed according to the 2007 WHO standard guidance. The presence of at least one shared allele (band) at any allelic family between D0 and DX samples at all genotyped loci is sufficient to provide evidence of recrudescence (participants 001–004, star denotes a shared allele). Notably, loss (participant 002), gain (participant 003), or both loss and gain (participant 004) of additional alleles is not evidence of new infection. Participant 005 would be classified as a new infection because there are no shared alleles at the msp2 locus at either allelic family. This figure appears in color at www.ajtmh.org.

Figure 2.

WHO classifications (left) for study participants in a therapeutic efficacy study, including the recommended approaches for calculating uncorrected and PCR-corrected efficacy (A–D). The final equation (E) is not a WHO-recommended approach but a common method observed in this systematic analysis. An example (right) using hypothetical data showing how WHO-endorsed calculation methods may yield an efficacy estimate with policy implications different from estimates obtained from calculations deviating from WHO-endorsed calculation methods (D vs. E; an efficacy threshold of < 90% is identified by the WHO as a trigger to reevaluate whether a drug should continue to be deployed as a first-line antimalarial). Hypothetical data used on the right: 110 subjects recruited, eight lost to follow-up, two withdrawn, one early treatment failure, 35 new infections, seven recrudescences, and 57 adequate clinical and parasitological response. ACPR = adequate clinical and parasitological response.

Figure 3.

Number of therapeutic efficacy reports by country, excluding multicountry studies (A). Frequency of excluding new infections from the final analyses (rather than including them as adequate clinical and parasitological responses [ACPR]) in the per-protocol analysis by country (B).

Figure 4.

Distribution of molecular genotyping methodologies used by studies using molecular correction in sub-Saharan Africa (n = 221), by locus combination (A) and individual frequency for each locus (B). SNP = single-nucleotide polymorphism. This figure appears in color at www.ajtmh.org.