cobas^® MTB-RIF/INH

Rapid resistance testing for proper therapy

Tuberculosis is a bacterial infection caused by species of the Mycobacterium tuberculosis (TB, MTB) complex. A drug resistant strain is defined as resistance to at least one primary drug used to treat tuberculosis. A multidrug resistant TB (MDR-TB) is defined as resistance to at least isoniazid and rifampicin, the two most effective anti-TB drugs, and an extensively drug resistant TB (XDR-TB) is defined as a MDR-TB strain with additional resistance to any fluoroquinolone and at least one injectable second-line TB drug (e.g., amikacin, kanamycin, or capreomycin). In 2017, it was estimated that >5% of incident new TB cases in the world had MDR/RR-TB. The frequency of MDR-TB varies according to region and is higher among previously treated patients.

cobas^® MTB-RIF/INH for use on the cobas^® 5800/6800/8800 Systems is an automated, qualitative real-time PCR test designed as a reflex test together with cobas^® MTB to detect Rifampicin-resistance associated mutations of the rpoB gene and Isoniazid-resistance associated mutations in the katG and inhA genes, of M. tuberculosis. The test is intended for use on either acid-fast bacilli (AFB) smear-positive or smear-negative, raw sputum, and digested and decontaminated (N-acetyl-L-cysteine/ NaOH treated) sputum and bronchial alveolar lavage (BAL) samples, that tested positive for M. tuberculosis complex by cobas^® MTB. Detection of wild-type MTB complex DNA serves as Internal Control to monitor the entire sample preparation and PCR amplification process. In addition, the test utilises a low titer positive and a negative control.

Molecular Diagnostic algorithm

Enabling a complete diagnosis is critical to ensure proper therapy is initiated. When patient presents with symptoms of tuberculosis, the cobas^® MTB test is performed. If positive, patient should be evaluated for drug resistance using cobas^® MTB-RIF/INH test. If negative, the cobas^® MAI test can be used to detect a nontuberculosis infection.

Intended use

cobas^® MTB-RIF/INH for use on the cobas^® 5800/6800/8800 Systems is an automated, qualitative in vitro diagnostic test, that utilises real-time polymerase chain reaction (PCR), for the direct detection of rifampicin-resistance associated mutations of the rpoB gene, and isoniazid-resistance associated mutations in the katG and inhA genes, of Mycobacterium tuberculosis, from human respiratory specimens. The test is intended for use on either acid-fast bacilli (AFB) smear-positive or smear-negative, raw sputum, and digested and decontaminated (N-acetyl-L-cysteine/ NaOH treated) sputum and bronchoalveolar lavage (BAL) samples, that tested positive for Mycobacterium tuberculosis complex (MTBC) by cobas^® MTB. This test is intended for use in conjunction with culture and drug susceptibility testing, and as a reflex test together with cobas^® MTB, as an aid in the diagnosis of infection with a multidrug resistant M. tuberculosis (MDR-TB).

Ordering information

Material Number	Product Name	Tests Per Unit
09040617190	cobas^® MTB-RIF/INH	192 T per cassette
09051953190	cobas^® MTB-RIF/INH Positive Control Kit	16 controls x 1mL each
09040625190	cobas^® 6800/8800 Buffer Negative Control Kit	16 controls x 1mL each
08185476001	cobas^® Microbial Inactivation Solution	16 bottles x 30mL each

Registration status

CE-IVD

Package inserts

Access package inserts through Roche DiaLog.

References

Global tuberculosis report 2018. Geneva: World Health Organization; 2018. Licence: CC BY-NC-SA 3.0 IGO.

Specifications and analytical performance

Sample volume

Sputum ≥ 0.4mL, Sediment ≥ 0.2mL
Specimen types

Raw Sputum, Sputum Sediment, Bronchoalveolar lavage (BAL)
Patient collection

Providing sufficient patient sample was collected, the cobas^® MTB-RIF/INH test can be run in conjunction with cobas^® MTB and cobas^® MAI tests without the duplication of the pre-analytic processing
Sample processing

Manual liquefaction and inactivation followed by sonication and automated amplification and detection on the cobas^® 5800/6800/8800 Systems
PCR target regions

Eighteen Rifampicin-resistance associated mutations (rpoB gene) and seven Isoniazid resistance associated mutations (katG gene and inhA gene promotor region) are detected by multiple primers and mutation specific probes.
Controls

Internal Control ensures sample validity. Test specific Positive Control and buffer Negative Control ensures run validity.
Inclusivity

rpoB gene mutations associated with rifampicin resistance:

L511P, Q513K, Q513L, Q513P, D516V, D516Y, S522L, S522Q, H526D, H526L, H526N, H526R, H526Y, S531L, S531W, L533P

katG gene mutations and inhA gene promoter region mutations associated with isoniazid resistance:

katG gene: S315I, S315N, S315T, S315T2

inhA gene promoter region: T-8A, T-8C, C-15T

The inclusivity for two more rpoB gene mutations associated with rifampicin resistance – S522W and D516G – was verified by testing plasmids
Analytical specificity

A panel of 145 bacteria, fungi and viruses, including those commonly found in respiratory tract did not interfere with the test by generating false positive results
Analytical sensitivity (Limit of detection)

RIF-resistant M. tuberculosis
    94.0 CFU/mL (sputum/BAL sediment)
    182 CFU/mL (raw sputum)
INH-resistant M. tuberculosis
    12.6 CFU/mL (sputum/BAL sediment)
    27.5 CFU/mL (raw sputum)
Endogenous interference

Not affected by the presence of elevated levels of gastric juice, haemoglobin, human whole blood, human DNA, mucin, pus and saliva
Exogenous interference

Not affected by the presence of 48 drugs and over-the-counter substances

Clinical performance

Heteroresistance

The ability to detect mutant MTB in a mixed infection with wild-type MTB was confirmed by testing different mutant to wild-type ratios. Low concentration levels of MDR MTB culture isolate (~3 x LoD) in a background of up to 60% wild-type MTB are detected by cobas^® MTB-RIF/INH in sputum and sediment samples.

cobas^® 5800, cobas^® 6800 and cobas^® 8800 Systems

The fully automated cobas^® 5800 and cobas^® 6800/8800 Systems offer fast time to results and flexible throughputs with long walk-away times, providing laboratories with improved efficiency and the flexibility to adapt to changing testing demands.

Ready-to-use reagents are stored at appropriate temperatures on the system with their expiration monitored. This enables the complete mycobacteria menu comprising cobas^® MTB, cobas^® MAI, and cobas^® MTB-RIF/INH to be seamlessly run with available menu (HIV, hepatitis, HPV and STI’s) for quality results that help speed proper treatment and reduce the spread of infection.

cobas® MTB-RIF/INH