Rapid diagnosis of tuberculosis and resistance profile is central to its control. Failure to quickly recognize and treat affected patients leads to increased mortality, secondary resistance (including extensively drug-resistant tuberculosis), and ongoing transmission.
A fully automated molecular test for TB case detection and drug resistance (rifampicin resistance) has been recently developed by the name of Xpert MTB/RIF which integrates sample processing and PCR in a disposable plastic cartridge containing all reagents required for bacterial lysis, nucleic acid extraction, amplification, and amplicon detection.
Processing involves three simple steps:
- Sputum liquefaction and inactivation with sample reagent (15 minutes)
- Transfer of material (from step 1) into test cartridge
- Insertion of cartridge into machine (Xpert MTB/RIF)
Subsequent processing is automated, and the results are provided in 1 hour and 45 minutes (total time from sputum processing to result: 2 hours). The results are provided in a printable version e.g. MTB detected; RIF resistance not detected.
Sensitivity: 99.8% in smear & culture positive and 90.2% in smear negative & culture positive (overall 97.6%)
Specificity: 99.2% overall
Rifampin resistance detection:
Point-of-treatment use, results available in the clinic and decision regarding therapy could be taken
No requirement of a biological safety cabinet
Minimum training required for test performer (2-3 days v/s 2 weeks for microscopy)
Simple to perform, minimum hands-on-time of 15 minutes
Unambiguous result readout
Cost of the equipment
Needs a reliable electricity supply and temperature maintenance
Requirement of annual calibration
Boehme CCN, P; Hillemann, D; Nicol, M.P; Shenai, S; Krapp, F. Rapid Molecular Detection of Tuberculosis and Rifampin Resistance. New Engl J Med. 2010.