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

Table 4 Performance of ELISA using calculated cutoff values from known negative controls at 99% confidence interval^a

	Scrub typhus positive determined by definition in Table 2
Parameters	Number or percentage of positives
ELISA results	IgG	IgM
True positive (TP)	81	70
True negative (TN)	141	150
False positive (FP)	21	12
False negative (FN)	5	16
Sensitivity	94.2	81.4
Specificity	87.0	92.6
Positive predict value (PPV)	79.4	85.4
Negative predict value (NPV)	96.6	90.4
Accuracy	89.5	88.7
Likelihood ratio positive (LR+)	7.27	11.0
Likelihood ratio negative (LR-)	0.07	0.20

^aTable shows number of samples for true positive, true negative, false positive and false negative. 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 values are greater than or equal to 0.816 for IgG or 0.320 for IgM

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