Bacteriological status refers to the detection of M. tuberculosis by smear, culture or molecular methods. The bacteriological status can be further sub-classified on the basis of drug sensitive and drug resistant cases.
7.4.1 Detection of M. tuberculosis
Every TB case should be classified into one of two categories:
– Confirmed TB case: a case with a positive bacteriological result (microscopy, culture or molecular method).
– Non-confirmed TB case: a case where investigations are negative (microscopy, culture or molecular method) and for whom a clinician prescribes anti-TB treatment.
Confirmed TB cases are further sub-classified as:
(1) smear positive/negative/not done
(2) culture positive/negative/not done
(3) molecular test positive/negative/not done
7.4.2 Strain sensitivity/resistance
When possible, culture and DST should be done to determine if the strain presents resistance to some drugs:
– Susceptible TB: the strain is not resistant to any first-line anti-TB drugs.
– Drug-resistant TB:
• Monodrug-resistant TB: resistance to one first-line anti-TB drug only;
• Polydrug-resistant TB (PDR-TB): resistance to more than one first-line anti-TB drug, other than isoniazid and rifampicin;
• Multidrug-resistant TB (MDR-TB): resistance to at least isoniazid and rifampicin;
• Extensively drug-resistant TB (XDR-TB): MDR-TB resistant to at least one fluoroquinolone and at least one second-line injectable drug (Km, Amk, Cm).
Patients with DR-TB should be classified in the following manner:
– Confirmed isoniazid resistance and rifampicin susceptible: resistance to isoniazid but not rifampicin. Resistance to first and second-line anti-TB drugs may be present.
– Confirmed rifampicin resistant TB (RR-TB): resistance to rifampicin confirmed by phenotypic drug susceptibility test or line probe assay or Xpert MTB/RIF (isoniazid susceptible or unknown).
– Confirmed MDR-TB: resistance to isoniazid and rifampicin, with or without resistance to first and second-line anti-TB drugs.
– Confirmed XDR-TB: resistance to isoniazid and rifampicin, and to at least one fluoroquinolone, and one second-line injectable drug (Km, Amk, Cm).
– Unconfirmed DR-TB: patients treated as DR-TB but without DST results (e.g. children who are contacts of a known case, patients with clinical failure and for whom no DST was available for some reason).