Fig. 2

Association between clinical dihydroartemisinin-piperaquine outcome and in vitro and ex vivo piperaquine survival assay (PSA) survival rates. In vitro and ex vivo PSAs were done with 0–3 h post-invasion rings from culture-adapted parasites isolated in 2012–2013 or parasites directly collected from patients with malaria in Rattanakiri, Siem Reap, Stung Treng, and Mondulkiri in 2014, respectively. Results from the in vitro and ex vivo PSAs are expressed as the proportion of viable parasites in the exposed or non-exposed cultures (Fig. 1). Isolates (collected on day 0) are dichotomized according to the clinical outcome of infection in patients enrolled and treated with a 3-day course of dihydroartemisinin-piperaquine (non-recrudescence or recrudescence of P. falciparum infections within 42 days, after PCR-correction). The median of the proportion of viable parasites was significantly higher in isolates from subsequently recrudescent than non-recrudescent patients (in vitro PSAs 51.9 % vs. 34.4 %, respectively, P = 0.04; ex vivo PSA: 39.2 % vs. 0.17 %, respectively, P <1 × 10^–11). Each circle represents a P. falciparum isolate. Red and green colors refer to K13 mutant alleles (C580Y or Y493H) and K13 wild-type alleles, respectively. The black diamonds, the horizontal lines and I bars represent the medians and interquartile ranges. The dotted grey line represents the 10 % survival rate cut-off that distinguishes piperaquine-resistant (≥10 %) from piperaquine-sensitive (<10 %) parasites in PSAs