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The molecular beacons targeting the rpoB gene cover all the mutations found in more than 99.5% of Mycobacterium tuberculosis rifampicin-resistant strains.

The molecular beacon consists of:

• Loop: 18-30 base pair region of the molecular beacon, which is complementary to the target sequence
• Stem: 5-7 bp complementary sequence on both the ends of the loop
• 5’ Fluorophore: Fluorescent dye covalently linked at the 5' end
• 3’ Quencher: Nonfluorescent dye covalently linked at the 3' end

Probe Check Control (PCC) of Cartridge Based Nucleic Acid Amplification Test (CBNAAT) Technology tests the fluorescence readings of probes at different temperatures, before the start of thermal cycling.

PCC verifies:

• Re-hydration of beads
• Filling of the Polymerase Chain Reaction (PCR) tube
• Integrity of probes
• Stability of a dye or the reagents/ quencher.

The results are automatically compared to the pre-established factory settings in the software.

In the Cartridge Based Nucleic Acid Amplification Test (CBNAAT) machine, Sample Processing Control (SPC) monitors sample processing.

Once the cartridge has been loaded into CBNAAT module, system control checks:

• The instrument and software readiness
• Conditions for sample processing
• The integrity of PCR reagents and PCR efficiency.

Instrument system check control verifies the:

• Optics
• Mechanical components
• Temperature of the module
• Physical integrity of each cartridge
• Favourable PCR reaction conditions.

If any aspect of system check control fails, an ERROR is reported.

The External Quality Assessment (EQA) for Fluorescent Microscopy (FM) follows the same basic principles as for sputum smear microscopy using Ziehl-Neelsen (ZN) staining:

1. On-site Evaluation (OSE)
2. Panel Testing
3. Random Blinded Re-checking

Differences between EQA for FM and sputum smear stained by ZN method:

One of the methods for internal monitoring of the quality of the microscopy process is the use of Quality Control (QC) slides.

QC is a systematic internal monitoring of working practices, technical procedures, equipment and materials, including quality of stains.

Quality Control Positive (QCP) and Quality Control Negative (QCN) slides are used for sputum smear microscopy quality monitoring.

Process for quality control using QCP and QCN is as follows:

The following are a few of the steps for comprehensive infection control measures:

Providing health education and counselling to each Drug-resistant TB (DR-TB) patient is an essential step in the management of DR-TB patients. 

It is important to consider the long duration of treatment and the multitude of factors that may influence the overall treatment continuation and success. 

The treatment duration of any DR-TB regimen is long enough for the patient who needs multiple sessions of counselling, preferably more frequently in the initial phase of treatment. 

The following figure depicts the flow of Drug Resistant-TB (DR-TB) patients from diagnosis of DR-TB to treatment initiation and follow-up till final treatment outcome submission for patients on a longer oral regimen. 

Figure: Flow of M/XDR-TB Patients on a Longer Oral Regimen; Source: Guidelines for PMDT, India, 2021, p108.

It is important to give proper doses of medicines to patients in second-line Multidrug-resistant TB (MDR-TB) regimens according to their weight band.

The tables below provide information on the dosing of medicines used in MDR-TB regimens by weight band for patients under 15 years.

Table 1: Dosing of Group A medicines used in MDR-TB regimens by weight band for patients under 15 years​;
Source: Annexure 15, PMDT Guidelines, India, 2021.