Drug-resistant TB patient classification and definition of terms

Clinical description

WHO recently developed standardised definitions, classification, registration and reporting systems to facilitate uniform communication of concepts related to drug-resistant TB. In general, strains of TB can either be susceptible or resistant to anti-TB drugs:

• Susceptible TB refers to a tuberculosis strain that is not resistant to any anti-TB drugs.
• Drug-resistant TB is confirmed through laboratory tests that show the infecting

isolates of MTB grow in vitro in the presence of one or more anti-TB drugs. (can also be confirmed by molecular test as Xpert MTB/RIF and FL/SL LPA)

Patterns of drug resistance A diagnosis of drug resistance is primarily a laboratory-based diagnosis. There are two broad methods in use in Malawi;

• Phenotypic: growing of MTB in a culture media which is inoculated with one or more

anti TB drugs. Solid culture method (using Lowenstein-Jensen medium) and liquid culture (using Mycobacteria Growth Indicator Tube (MGIT)).

• Genotypic: LPA and Xpert MTB/RIF. Xpert MTB/RIF only detects rifampicin resistance.

Classif ication based on drug resistance pattern

• Patients with TB can either be bacteriologically confirmed or clinically diagnosed.

Bacteriological confirmation can either be through molecular methods, culture or smear microscopy.

• Clinically diagnosed patients subsequently found to be bacteriologically positive

74 National Tuberculosis Control Programme should be reclassified as bacteriologically confirmed.

• Bacteriologically confirmed patients are further classified based on resistance to the

main drugs, based on laboratory diagnosis by genotypic and/or phenotypic Drug Susceptibility tests as follow:

 Mono-resistant TB: Resistance to one first-line anti-TB drug  Poly-resistant TB: Resistant to more than one first-line anti-TB drug other than rifampicin and isoniazid  Multi-drug resistant TB (MDR-TB): Resistance to rifampicin and isoniazid with or without resistance to other medicines  Extensively drug-resistant TB (XDR-TB): MDR resistance pattern + resistance to any fluoroquinolone + resistance to at least one of the three second-line injectable (Capreomycin, Kanamycin, Amikacin)

 Rifampicin Resistant TB (RR–TB): Resistance to Rifampicin using genotypic or phenotypic methods regardless of whether there is documented resistance to other first- or second-line anti TB agents. (It includes any resistance to rifampicin, in a form of mono, poly, Multi or Extensive Drug resistance).

 Any patient who falls into one of the above listed types of drug-resistance is considered a drug-resistant TB patient.

10.3.4 Classif ication of drug-resistant TB based on laboratory conf irmation Registration group based on history of anti-TB treatment All RR-/MDR-TB patients must be registered as per the history of anti-TB treatment. Patients should be classified in two ways:

Classification as per history of anti-TB treatment is used mainly to assign the appropriate treatment regimen. Registration groups are:

• New: A patient who has received no or less than one month of anti-tuberculosis

treatment.

• Previously treated with first-line drugs: a patient who has received first-line anti-TB

treatment for four weeks or more.

• Previously treated with second-line drugs: a patient who has received second-line

anti-TB treatment for four weeks or more.

Classification is determined by history of treatment at the time of collection of the sample that was used to confirm DR-TB. Previous history refers to outcome of the latest TB treatment of the patient.

Registration groups are:

New: A patient who has received no or less than one month of anti-tuberculosis treatment.

National Tuberculosis Control Programme 75 Relapse: A patient who was previously treated for TB and whose most recent treatment outcome was “cured” or “treatment completed”, and who is subsequently diagnosed with a recurrent episode of TB (either a true relapse or a new episode of TB caused by reinfection), either bacteriologically confirmed or clinically diagnosed Treatment after being lost to follow-up: A patient who had previously been treated for TB and was declared lost to follow-up at the end of the most recent course of treatment After failure of first treatment with first-line drugs: A patient who has received first-line drug treatment for TB and in whom treatment has failed.

After failure of retreatment regimen with first-line drugs: A previously treated TB patient who has received a retreatment regimen with first-line drugs and in whom the retreatment has failed.

Transfer-in: A patient who has been transferred from another MDR-TB registration site to continue MDR-TB treatment.

Other previously treated: refers to any DR-TB patient who does not fit into any of the above categories.