TABLE 2.

Comparison of laboratory characteristics between (partially) semi-immune and nonimmune travelers with imported malaria based on studies stratified by immunity status

Reference	Country	Study design	Population(s)	Outcome(s)a	Findings
Behrens-Riha et al. (118)	Germany	Matched case-control study	(i) Semi-immune malaria patients and controls (n = 71); (ii) nonimmune malaria patients and controls (n = 349)	Peripheral blood MLCR	Both median (IQR) NLCR and MLCR were higher in nonimmune malaria cases than in controls (2.88 [1.66 to 5.19] versus 1.7 [1.2 to 2.4], P < 0.001, and 0.32 [0.17 to 0.52] versus 0.16 [0.1 to 0.25], P < 0.001); for semi-immune patients there was weak evidence for such differences; median (IQR) MLCR was 0.2 (0.1 to 0.35) in cases and 0.1 (0.07 to 0.21) in controls (P = 0.19), while median (IQR) NLCR was 1.86 (1.31 to 3.19) in cases and 1.69 (0.77 to 2.83) in controls (P = 0.53)
				NLCR	Nonimmune patients with an MLCR of ≥0.27 had 5.92-fold higher adjusted odds (95% CI, 3.66 to 9.59) to be a malaria case than a control; this equaled a sensitivity and specificity of an MLCR of ≥0.27 to detect malaria of 59% and 80%, respectively, in nonimmune patients; for semi-immune patients there was insufficient evidence for a similar effect (OR, 3.9 [95% CI, 0.5 to 27.43]; P = 0.20); however, the MLCR cutoff was set at ≥0.15; concordantly, nonimmune patients with an NLCR of ≥0.25 had an adjusted OR of 5.24 (95% CI, 3.25 to 8.45) to be malaria positive than malaria negative, while for semi-immune patients with an NLCR of ≥0.15 there again was no sufficient evidence for a similar effect (P = 0.98); however, the sensitivity and specificity of an NLCR of ≥0.25 to detect severe malaria in semi-immune patients were 63.6% and 80%, respectively
Chiwakata et al. (126)	Germany	Prospective	(i) Nonimmune patients with uncomplicated malaria (n = 20); (ii) semi-immune patients with uncomplicated malaria (n = 16); (iii) patients with severe malaria (n = 30)	Procalcitonin	Nonimmune patients with uncomplicated malaria had a geometric mean concentration of 1.1 ng/ml, semi-immune patients with uncomplicated malaria of 2.4 ng/ml, and those with severe malaria of 10.7 ng/ml (P < 0.001)

^aMLCR, monocyte-to-lymphocyte count ratio; NLCR, neutrophil-to-lymphocyte count ratio.