A new droplet digital PCR assay: improving detection of paucibacillary smear-negative pulmonary tuberculosis.

Objectives: Smear-negative pulmonary TB (PTB) is difficult to diagnose. Current diagnosis and treatment monitoring methods have inherent limitations. Droplet digital PCR (ddPCR) is a new technique with high sensitivity. This study presents a novel ddPCR for rapid and sensitive identification of Mycobacterium tuberculosis (MTB).

Methods: MTB DNA was detected in respiratory specimens from suspected PTB cases using ddPCR assay, which was directed at two different locations within IS6110. We, for the first time, evaluated the clinical diagnostic ability of this ddPCR for paucibacillary smear-negative PTB.

Results: A total of 605 PTB suspects were recruited, including 263 patients with confirmed PTB (84.03% from smear-negative PTB) and 342 without PTB. The sensitivity and specificity of IS6110 ddPCR were 61.22% (95% confidence interval (CI) 55.00-67.10%) and 95.03% (95% CI 92.20-97.10%) for total PTB and 57.92% (95% CI 51.10-64.50%) and 94.57% (95% CI 91.20-96.90%) for smear-negative PTB. ddPCR assay outperformed Xpert MTB/RIF (53.08% vs 28.46%, P = 0.020) in smear-negative PTB detection. Furthermore, effective anti-TB treatment was linked to significantly lower IS6110 copies detected by ddPCR.

Conclusion: Herein, we developed and validated a highly sensitive and robust ddPCR assay for MTB quantification in respiratory specimens, which improves diagnosis and therapeutic effect evaluation of smear-negative PTB.