Table 1.

Comparison of the accuracy and performance characteristics of assays for acute diagnosis of scrub-typhus infection

Format	Assay	Acute sensitivity	Specificity	Cost/sample	Time	Ease	Setting	Comments
Isolation	In vitro isolation (cell culture)9	+	+++++	+++++	7–60 days	+	BSL3 reference laboratory	•Isolation of BSL3 agent •Requires infrastructure •Biocontainment issues •Retrospective diagnosis
Isolation	Mouse inoculation10	+	+++++	+++++	5–30 days	+	BSL3 reference laboratory	•Technically demanding •Isolation of BSL3 agent •Requires animal facilities •Biocontainment issues •Retrospective diagnosis
Serology	IFA19	++	+++	++++	2 hours	++	Reference laboratory/hospital	•Serology gold standard •Requires propagation and purification of BSL3 agents as antigen for assay •Requires fluorescence microscope •Standardization problems •Requires paired samples (retrospective diagnosis)
Serology	IIP3	++	+++	+++	2 hours	++++	Reference laboratory/Hospital	•Serology gold standard •Requires propagation and purification of BSL3 agents as antigen for assay •Requires light microscope only •Standardization problems •Requires paired samples (retrospective diagnosis)
Serology	Weil–Felix OX-K20	+	++	+	6–18 hours	++++	Primary hospital	•Poor sensitivity for acute disease •Requires paired samples (retrospective diagnosis)
Serology	Rapid point-of-care tests (e.g., Integrated Diagnostics Dip-S-Ticks)20	++	+++	+++	< 30 minutes	+++++	Primary hospital	•Does not require specialized equipment •Rapid and simple
Genetic	Real-time PCR (16S, 56 kDa, 47 kDa, groEL)13,15	+++	+++++	+++	3 hours	+++	Reference laboratory/hospital	•Expensive equipment •Requires infrastructure •Sensitivity dependent on sample type and timing •Possible contamination issues
Genetic	Loop amplification (groEL)13	+++	+++++	++	2 hours	++++	Primary hospital	•Simple •Inexpensive •Possible contamination issues

BSL3 = biosafety level 3; + = low/poor; +++++ = high/excellent on a five-point qualitative scale.