Rapid diagnosis of tick-borne illnesses by use of one-step isothermal nucleic acid amplification and bio-optical sensor detection

BACKGROUND: Scrub typhus and severe fever with thrombocytopenia syndrome (SFTS) are the most common tick-borne illnesses in South Korea. Early differentiation of SFTS from scrub typhus in emergency departments is essential but difficult because of their overlapping epidemiology, shared risk factors, and similar clinical manifestations. METHODS: We compared the diagnostic performance of one-step isothermal nucleic acid amplification with bio-optical sensor detection (iNAD) under isothermal conditions, which is rapid (20 –30 min), with that of real-time PCR, in patients with a confirmed tick-borne illness. Fifteen patients with confirmed SFTS who provided a total of 15 initial blood samples and 5 follow-up blood samples, and 21 patients with confirmed scrub typhus, were evaluated. RESULTS: The clinical sensitivity of iNAD (100%; 95% CI, 83–100) for SFTS was significantly higher than that of real-time PCR (75%; 95% CI, 51–91; P 0.047), while its clinical specificity (86%; 95% CI, 65–97) was similar to that of real-time PCR (95%; 95% CI, 77–99; P 0.61). The clinical sensitivity of iNAD for scrub typhus (100%; 95% CI, 81–100) was significantly higher than that of real-time PCR for scrub typhus (67%; 95% CI, 43– 85; P 0.009), while its clinical specificity (90%; 95% CI, 67–98) was similar to that of real-time PCR (95%; 95% CI, 73–100; P 0.99). CONCLUSIONS: iNAD is a valuable, rapid method of detecting SFTS virus and Orientia tsutsugamushi with high clinical sensitivity and specificity.