SUPRA-NATIONAL REFERENCE LABORATORY

NETWORK

Possible research projectsA. Van Deun

1. RELEVANCE OF BORDERLINE R-RESISTANCE

• Background: SRL rounds– too many discordant strains in Rounds

– all with documented Rr-conferring mutation

– WT fraction not visible by sequencing, so hetero-resistance or mixture cannot explain the discordance?

• Background: clinical experience– poor results Cat. 2 retreatment after 6-months R Cat. 1

– far more failures within same (non-MDR) resistance-group than with weaker Cat 1

low-level Rr missed in retreatment cases??

Number/total % Number/total %

Susceptible 76 / 4124 2 35 / 447 8

H(+)r, non-MDR 17 / 429 4 21 / 108 19

MDR 39 / 164 24 57 / 140 41

*Espinal M A, Kim S J, Suarez P G et al.

Standard short-course chemotherapy for drug-resistant tuberculosis. JAMA 2000; 283: 2537-45

Failure outcome by initial resistance class; recalculated from Espinal 2000*, transfers excluded

Cat 1, R-throughout Cat 2

STUDY OUTLINE• Testing R at 20 and 40 µg/ml (or corresponding)

– recommended in Canetti 1969 proportion method ref. paper– MIC 30-40 for +/- 10% probably R-resistant at coordinating lab

document frequency R20r/R40s

• Use QA strains from random sampling surveys– request all retreatment strains for QA, including susc.– also collect outcome of treatment information (including relapse)

• All strains for monitoring of resistance in retreatment strains (and DOTS-Plus)– if randomly sampled– i.e. systematic FU of Cat 1 / Cat 2 retreatments in SRL in HBC

ACCURACY OF GENOTYPIC DST FOR R

• Background:– literature: about 95% correlation– discordants: no mutation but phenotypic Rr– however:

• too few phenoypic R-susceptible checked in these studies

• clinical significance of pheno-Rr / geno Rs ??

STUDY OUTLINE

• Combine with first proposal on discordants

• Same group of strains – random and representative samples from retreatment cases

• Do also rpoB sequencing (or hybridisation)– cluster 1 or extended?– document outcome of standard treatment !!

but MDR-TB treatment would interfere

so only projects without DOTS-Plus in place?

RELEVANCE OF E-TESTING

• Background– high error-rates, lower reproducibility, discordance

between systems (LJ versus BACTEC/MGIT)– interpretation problems:

• potency adjustment or not?• microcolonies (at 4 weeks? at 6 weeks?)

– significance??• Er but still synergistic with amoxy-clavulanic in vitro• replacement by cycloserin in MDR-regimens

– not done in standardised regimen in Bangladeshcured : 98/122 (80%) of cured have HRE(S) resistant strain

versus 7/9 (78%) of the failures

STUDY OUTLINE

• Study populations from DRS surveys – meta-analysis, lump surveys together?– only Cat 1 : 2EHRZ/6HE– failure / relapse (F/R) outcome

• initally H(S)r versus initially H(S)Er• stratify for exact critical concentration (E-potency

adjustment!); and method?

– if possible: compare also acquired Rr in F/R strains, same arms (cf. Vietnam experience with 2SHRZ/6HE failures: 40% ADR to R)

KANAMYCIN / ETHIONAMIDE / OFLOXACIN

• Background

– may be more important in panel than E and S

(DOTS-Plus)

– but not well standardised for LJ

– and clinical significance less known

• K resistance level and amikacin activity ?

• O resistance level and moxi, gati activity ?

• ETH / INH cross-resistance clinical relevance?

STUDY PROPOSAL

• Standardise K, O and ethionamide for LJ proportion method / other systems?

• Document MIC values and determine critical concentrations– K, Ethion: outcome of MDR-TB standard

regimen including K, thioamide (and quinolone susceptible)

– O: outcome of MDR-TB standard regimen including moxi or gati (and other second-line susceptible)