Fig. 2.

The parasite positivity rate (PPR) as a parasite clearance metric. The PPR at day 3 is defined by the proportion of a population with detectable parasitemia 3 days following treatment initiation. Therefore, for each individual, it reflects a binary outcome according to whether the X-intercept of the parasite clearance curve (also defined as the parasite clearance time) occurs before or after day 3 (dashed line). Whether this occurs or not will depend on the Y intercept (P: the parasite density at treatment commencement) and the gradient of the parasite clearance curve (k: the rate at which parasites are cleared). k will be determined by intrinsic parasite sensitivity (and therefore decrease when drug resistance develops) but may also be affected by pharmacological (e.g. pharmacokinetic variability) and host factors (acquired malaria-specific immunity will augment parasite killing and therefore increase the gradient)