An ELISA assay using a combination of recombinant proteins from multiple strains of Orientia tsutsugamushi offers an accurate diagnosis for scrub typhus

Table 5 Performance of ELISA using cutoff values generated by ROC curves^a

	Scrub typhus positive determined by definitions in Table 2
Parameters	Number or percentage of positives
ELISA results	IgG	IgM
Area under curve (ARC)	95.3	91.7
J (Sensitivity + Specificity – 1)	0.85	0.76
True positive (TP)	78	70
True negative (TN)	153	154
False positive (FP)	9	8
False negative (FN)	8	16
Sensitivity	90.7	81.4
Specificity	94.4	94.4
Positive predict value (PPV)	89.7	88.6
Negative predict value (NPV)	95.0	90.5
Accuracy	93.1	89.9
Likelihood ratio positive (LR+)	16.3	14.7
Likelihood ratio negative (LR-)	0.10	0.20

^aTable shows number of samples for true positive, true negative, false positive and false negative. AUR, sensitivity, specificity, PPV, and, NPV are shown as percentage. The likelihood ratio was determined by using the following formulas: LR+ = sensitivity/ (1 – specificity), LR- = (1-sensitivity)/specificity. Samples are considered ELISA positive if the OD exceeds or equals to 1.305 for IgG and 0.3595 for IgM

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