Factors affecting rosetting formation in P vivax and P falciparum. (A) Comparison of rosetting rate between P vivax and P falciparum isolates from the Thailand-Myanmar border. The median percentage of P vivax IRBCs is significantly higher than P falciparum; P (2-tailed) < .001. (B) Rosetting rate of P vivax and P. falciparum isolates found in different human ABO blood groups. No significant association was found between ABO phenotype of the malaria and occurrence of P vivax (P = .28) or P falciparum (P = .20). (C) Plot of rosetting rate of P vivax and P falciparum isolates against the original parasitemia of malaria patients presenting for treatment. No significant correlation was observed between patient parasitemia and rosetting for P vivax (Spearman r = −0.10; 95% CI [−0.39 to 0.20]; P = .50) or P falciparum (Spearman r = −0.06; 95% CI [−0.38 to 0.27]; P = .71). (D) Rosetting rate of P vivax and P falciparum isolates against peripheral reticulocyte counts in malaria patients. No significant correlation was observed between rosetting and patient reticulocyte counts for either P vivax (Spearman r = 0.33; 95% CI [−0.04 to 0.62]; P [2-tailed] = .07) or P falciparum (Spearman r = −0.13; 95% CI [−0.49 to 0.28]; P = .52).