Background: Meta-analyses on impact of isoniazid-resistant tuberculosis informed the World Health Organization recommendation of a levofloxacin-strengthened rifampicin-based regimen. We estimated the effect of initial rifampicin resistance (Rr) and/or isoniazid resistance (Hr) on treatment failure or relapse. We also determined the frequency of missed initial and acquired Rr to estimate the impact of true Hr. Methods: Retrospective analysis of 7291 treatment episodes with known initial isoniazid and rifampicin status obtained from individual patient databases maintained by the Damien Foundation Bangladesh over 20 years. Drug susceptibility test results were confirmed by the programme's designated supra-national tuberculosis laboratory. To detect missed Rr among isolates routinely classified as Hr, rpoB gene sequencing was done randomly and on a sample selected for suspected missed Rr. Results: Initial Hr caused a large recurrence excess after the 8-month regimen for new cases (rifampicin for two months), but had little impact on rifampicin-throughout regimens: (6 months, new cases; 3.8%; OR 0.8, 95%CI:0.3,2.8; 8 months, retreatment cases: 7.3%, OR 1.8; 95%CI:1.3,2.6). Rr was missed in 7.6% of randomly selected "Hr" strains. Acquired Rr was frequent among recurrences on rifampicin-throughout regimens, particularly after the retreatment regimen (31.9%). It was higher in mono-Hr (29.3%; aOR 3.5, 95%CI:1.5,8.5) and poly-Hr (53.3%; aOR 10.2, 95%CI 4.4,23.7) than in susceptible tuberculosis, but virtually absent after the 8-month new case regimen. Comparing Bangladesh (low Rr prevalence) with a high Rr prevalence setting,true Hr corrected for missed Rr caused only 2–3 treatment failures per 1000 TB cases (of whom 27% were retreatments) in both. Conclusions: Our analysis reveals a non-negligible extent of misclassifying as isoniazid resistance of what is actually missed multidrug-resistant tuberculosis. Recommending for such cases a "strengthened" regimen containing a fluoroquinolone provokes a direct route to extensive resistance while offering little benefit against the minor role of true Hr tuberculosis in rifampicin-throughout first-line regimen.
Tuberculosis (TB) became curable with the introduction of isoniazid (INH; H).[[
Because of poor results, in the early eighties standardized regimens with RMP were piloted in low-income countries by the late Dr. Styblo of the International Union against Tuberculosis and Lung Disease. In the East African settings this first "short-course" 8-month regimen (2SHRZ/6HT; PZA, Z: pyrazinamide was used (with the HIV epidemic modified to 2EHRZ/6HE; EMB, E: ethambutol)[[
A 1986 review of clinical trials showed that RMP-throughout regimens were nearly as efficacious in patients with initial resistance to INH and/or SM compared to patients with susceptible TB (3.5% versus 0.5% treatment failure).[[
We studied the outcome of treatment of bacteriologically positive pulmonary TB cases with various standard regimens in function of initial INH and/or RMP resistance, using data from the Damien Foundation Bangladesh (DF) project. In this project continuous drug resistance surveillance of failure and relapse cases has been a priority from the start, supplemented by periodic random population surveys.[[
This retrospective cohort study is based on TB patients treated in DF supported clinics in Bangladesh between 1994 and 2015.
Since 1993 the DF Bangladesh project implements the TB treatment and care as partner in the National TB Programme (NTP). The first standardized treatment regimen for new patients was 2(
In 2008 auramine-based LED fluorescence microscopy was phased in as replacement for brightfield Ziehl-Neelsen microscopy for acid-fast bacilli (AFB). By 2015 it was used in 75% of the over 100 field laboratories. Quality assessment of all microscopy laboratories continuously documented high-quality performance.[[
From 2012 onward an Xpert
Between 1995 and 2015, Rr and Hr prevalence remained stable in new patients, around 1% and 5% respectively. With the change to the 6-month Category 1 regimen, Rr rose from 8% to 50% while Hr fell from 33% to 8% among retreatment patients.[[
We used routine patient, reference laboratory, and specific study databases to link information on pre-existing drug resistance to treatment outcome. Individual first-line patient databases containing most information from routine treatment cards were maintained systematically until the end of 2013. Each patient treatment episode was given a unique identifier. The database was periodically updated for bacteriologically positive recurrence subsequent to successful treatment completion. If a recurrence was declared within two years after cure or completion it was defined as relapse. Culture and/or DST results were retrieved from the DF Bangladesh reference laboratory database on continuous drug resistance surveillance among presumed drug-resistant cases (retreatments, late converters, new cases contacts of Rr TB, but almost no new cases), as described.[[
Databases were conceived and handled in EpiData Entry 3.1 (EpiData Association, Odense, Denmark). Single data entry of the close to 300,000 records was combined with regular checks and corrections by layers of supervisors. Database cleaning, in particular checking registered outcomes against recorded smear results and consistent recurrence definitions was done for all DRS and study databases prior to analysis, while the reference laboratory database was cleaned annually.
The information recorded in the treatment as well as reference laboratory databases included a unique patient-treatment-episode identifier, as well as a unique lifetime patient-identifier, the latter issued only to patients presumed or confirmed to have drug resistance. The various identifiers allowed correctly linking laboratory and patient information. Twenty-three linked records were excluded because the link was clearly erroneous when comparing patient initials, age, and sex from the two parent databases.
DST results from different samples tested for the same treatment episode and indication were condensed into a single record in which any positive culture or a resistant DST result overrode other values.
DST results obtained 60 or more days after treatment initiation were excluded, since drug resistance might already have been amplified from baseline by that time. Linked records with a resistance profile obtained more than 90 days before treatment start were also excluded, as possibly belonging to a previous treatment episode.
A resistant RMP result from any of the reference laboratories and by any technique overrode all other results for the same condensed record. Missed RMP resistance shown by rpoB sequencing had been added to the database for suspected strains selected for previous studies, and if present, this result was used for analysis. Comparing exclusively phenotypic DST-based profiles with those including an eventually present overriding molecular Rr result, corrected missed Rr amounted to 4% of all Rr. Over the last 20 years, the Antwerp SRL has been among those with the highest sensitivity for RMP resistance detection in the WHO annual rounds of DST EQA for the SRL global network (unpublished data from annual reports received by our SRL).
Initial Hr included mono-resistance (mono-Hr) and poly-resistance (poly-Hr; defined here as resistance to isoniazid plus EMB (HE) and/or SM (HES or HS), while susceptible to RMP). Initial Hr was assessed in the entire study population.
Rr in baseline samples was defined as missed Rr if routine phenotypic DST showed Rs-TB but Sanger rpoB sequencing done a posteriori at the SRL showed Rr [[
Rr in recurrence samples was defined as acquired Rr if the baseline sample for the same episode showed Rs-TB. Acquired Rr was assessed in all patients with initial Rs-TB for whom a DST results for a recurrence sample were available.
Successful outcomes were cure or treatment completion without bacteriological proof of relapse during the first two years after treatment. Death, lost to follow-up, treatment failure or relapse were defined as programmatically adverse outcomes. Bacteriologically adverse outcomes were AFB smear microscopy-based treatment failure or relapse. NTP and WHO guidelines and definitions were strictly followed. The smear microscopy cut-off for diagnosis as well as declaration of failure or relapse was at least 1 acid-fast bacillus (AFB) in at least 1 smear.
Univariable and multivariable logistic regression was used to identify factors, such as initial resistance profile and treatment regimen, that might be associated with treatment outcomes, programmatic or bacteriological, missed Rr, and acquired Rr. We show (adjusted) odds ratios (OR) and 95% confidence intervals (CI).
The DF Bangladesh environment is a low MDR-TB setting. To evaluate our calculations for a corrected Hr frequency, we used a data set from Georgia with a high MDR prevalence, applying our methodology to it to have an external comparison using our approach to settings with a different epidemiology. We selected Georgia's published data set because the required data were readily available, [[
The study protocol was approved by the Institutional Review Board of the ITM, Antwerp, Belgium; since it concerned anonymous routinely collected data, the requirement for informed consent was waived.
Fig 1 shows the study population. The subpopulations in which missed (N = 382) or acquired (N = 242) Rr were studied, were part of the main effectiveness population of 7291 cases. Patients who were chosen for DST had been selected randomly among successively registered cases or systematically among incident retreatment cases, with high risk of drug-resistant TB. New, previously untreated cases were not systematically tested and not included in this database, with the exception of symptomatic MDR-TB contacts (N = 47).
Graph: Fig 1 Flowchart showing the analysed populations.INH: isoniazid; RMP: rifampicin; EMB: ethambutol; SM: streptomycin; DST: drug susceptibility testing; TB: tuberculosis.
Table 1 shows programmatical and bacteriological effectiveness for 7291 treatment episodes, stratified by treatment regimens and by initial resistance profile. Patients with Hs/Rs-TB treated with 2(
Graph
Table 1 Treatment outcomes of 7291 patients on first-line TB treatment regimens in Bangladesh, by initial resistance to rifampicin and isoniazid.
Total Failure Relapse Died LTFU Relapse-free success Programmatical effectiveness Bacteriological effectiveness N N % N % N % N % N % % 2(3)EHRZ/6HT Total 1471 52 3.5 30 2 68 4.6 85 5.8 1236 84.0 93.8 Susceptible to INH and RMP 1349 31 2.3 17 1.3 62 46 77 5.7 1162 86.1 96.0 RMP resistance 20 6 30.0 3 15 1 5.0 2 10.0 8 40.0 47.1 INH mono-resistance 66 7 10.6 3 4.5 5 7.6 4 6.1 47 71.2 82.5 INH poly-resistance 35 7 20.0 7 20.0 0 0.0 2 5.7 19 54.3 57.6 INH resistance, unknown whether mono- or poly-resistance 1 1 100.0 0 0.0 0 0.0 0 0.0 0 0.0 0.0 2(3)EHRZ/4H3R3 Total 358 10 2.8 10 2.8 14 3.9 24 6.7 300 83.8 93.8 Susceptible to INH and RMP 331 5 1.5 9 2.7 13 3.9 24 7.3 280 84.6 95.2 RMP resistance 6 3 50.0 1 16.7 1 16.7 0 0.0 1 16.7 20.0 INH mono-resistance 6 0 0.0 0 0.0 0 0.0 0 0.0 6 100.0 100.0 INH poly-resistance 2 2 100.0 0 0.0 0 0.0 0 0.0 0 0.0 0.0 INH resistance, unknown whether mono- or poly-resistance 13 0 0.0 0 0.0 0 0.0 0 0.0 13 100.0 100.0 2(3)EHRZ/4HR Total 1018 43 4.2 11 1.1 31 3 28 2.8 905 88.9 94.4 Susceptible to INH and RMP 928 34 3.7 8 0.9 26 2.8 27 2.9 833 89.8 95.2 RMP resistance 23 8 34.8 2 8.7 3 13.0 0 0.0 10 43.5 50.0 INH mono-resistance 9 1 11.1 1 11.1 1 11.1 1 11.1 5 55.6 71.4 INH poly-resistance 8 0 0.0 0 0.0 0 0.0 0 0.0 8 100.0 100.0 INH resistance, unknown whether mono- or poly-resistance 50 0 0.0 0 0.0 1 2.0 0 0.0 49 98.0 100.0 2EHRhZ/4HRh Total 391 11 2.8 4 1.0 5 1.3 10 2.6 361 92.3 96.0 Susceptible to INH and RMP 370 11 3 4 1.1 5 1.4 10 2.7 340 91.9 95.8 RMP resistance 1 0 0.0 0 0.0 0 0.0 0 0.0 1 100.0 100.0 INH resistance, unknown whether mono- or poly-resistance 20 0 0.0 0 0.0 0 0.0 0 0.0 20 100.0 100.0 2SEHRZ/1(2)EHRZ/5EHR Total 4053 288 7.1 138 3.4 246 6.1 361 8.9 3020 74.5 87.6 Susceptible to INH and RMP 2759 47 1.7 57 2.1 153 5.5 232 8.4 2270 82.3 95.6 RMP resistance 571 204 35.7 70 12.3 65 11.4 63 11.0 169 29.6 38.1 INH mono-resistance 387 13 3.4 8 2.1 12 3.1 35 9.0 319 82.4 93.8 INH poly-resistance 332 23 6.9 3 0.9 16 4.8 30 9.0 260 78.3 90.9 INH resistance, unknown for whether mono- or poly-resistance 4 1 25.0 0 0.0 0 0 1 25.0 2 50.0 66.7
1 INH or H: isoniazid; RMP or R: rifampicin; E: ethambutol; S: streptomycin; T: thioacetazone; Z: pyrazinamide; h superscript: high-dose; LTFU: lost to follow-up
- 2 Preceding numbers in regimens are months of treatment; subscript numbers indicate intermittent number of doses of preceding drug per week
- 3
† Regardless of resistance to INH - 4
‡ INH poly-resistance: includes HS-resistant TB, HE-resistant TB, and HES-resistant TB (H = isoniazid; S = streptomycin; E = ethambutol). The vast majority is HS-resistant TB - 5
§ Programmatical effectiveness: cure or completion against the same plus failure and relapse, death or LTFU - 6
# Bacteriological effectiveness: cure or completion against the same plus failure and relapse
Among patients with Hs/Rs-TB, treatment with Category 2 more likely resulted in a programmatically adverse outcome (vs. 6-month RMP-throughout regimen; OR 1.8; 95%CI 1.5–2.1; Table 2). However, treatment regimen was not associated with having a bacteriologically adverse outcome (failure or relapse).
Graph
Table 2 Effect of treatment regimen on outcome, by initial resistance profile, in 7291 patients.
Programmatically adverse outcome Bacteriologically adverse outcome Total n % OR [95%CI] Total n % OR [95%CI] Initially susceptible to RMP and INH 6-month RMP-throughout regimen 1629 176 10.8 1 1524 71 4.7 1 2(3)EHRZ/6HT 1349 187 13.9 1.3* [1.1,1.7] 1210 48 4.0 0.8 [0.6,1.2] 2SEHRZ/1(2)EHRZ/5EHR 2759 489 17.7 1.8 [1.5,2.1] 2374 104 4.4 0.9 [0.7,1.3] Initially resistant to RMP 6-month RMP-throughout regimen 30 18 60.0 1 26 14 53.8 1 2(3)EHRZ/6HT 20 12 60.0 1 [0.3,3.2] 17 9 52.9 1 [0.3,3.3] 2SEHRZ/1(2)EHRZ/5EHRE 571 402 70.4 1.6 [0.7,3.4] 443 274 61.9 1.4 [0.6,3.1] RMP susceptible, INH resistant 6-month RMP-throughout regimen 108 7 6.5 1 105 4 3.8 1 2(3)EHRZ/6HT 102 36 35.3 7.9 [3.3,18.7] 91 25 27.5 9.6 [3.2,28.7] 2SEHRZ/1(2)EHRZ/5EHR 723 142 19.6 3.5 [1.6,7.8] 629 48 7.6 2.1 [0.7,5.9]
- 7 INH or H: isoniazid; RMP or R: rifampicin; E: ethambutol; S: streptomycin; T: thioacetazone; Z: pyrazinamide; OR: odds ratio
- 8 Preceding numbers in regimens are months of treatment; subscript numbers indicate intermittent number of doses of preceding drug per week
- 9 Level of significance:
- 10 ** p<0.01;
- 11 *** p<0.001
- 12
† programmatically adverse: failure, relapse, death or LTFU - 13
‡ bacteriologically adverse: failure or relapse - 14
§ either 2(3 )EHRZ/4H3 R3 , 2(3 )EHRZ/4HR, or 2EHRh Z/4HRh
Among patients with Rr-TB bacteriological adverse outcomes were frequent, ranging between 52.9% and 61.9%, and there were no significant differences between regimens.
Among patients with Hr/Rs-TB, 27.5% experienced either failure or relapse when treated with 2(
Among patients treated with the 6-month RMP-throughout regimen, initial Hr had no statistically significant effect on outcome if the strain was susceptible to RMP (Table 3). This was not the case for other regimens. Among patients treated with 2(
Graph
Table 3 Effect of initial resistance on outcomes, by treatment regimen, in 7291 patients.
Programmatically adverse outcome Bacteriologically adverse outcome Total n % OR [95%CI] Total n % OR [95%CI] 6-month RMP-throughout regimen Susceptible to INH and RMP 1629 176 10.8 1 1524 71 4.7 1 RMP resistant 30 18 60.0 12.4 [5.9,26.1] 26 14 53.8 23.9 [10.7,53.5] RMP susceptible, INH resistant 108 7 6.5 0.6 [0.3,1.3] 105 4 3.8 0.8 [0.3,2.3] 2(3)EHRZ/6HT Susceptible to INH and RMP 1349 187 13.9 1 1210 48 4.0 1 RMP resistant 20 12 60.0 9.3 [3.8,23.1] 17 9 52.9 27.2 [10.1,73.7] RMP susceptible, INH resistant 102 36 35.3 3.4 [2.2,5.2] 91 25 27.5 9.2 [5.3,15.8] 2SEHRZ/1(2)EHRZ/5EHR Susceptible to INH and RMP 2759 489 17.7 1 2374 104 4.4 1 RMP resistant 571 402 70.4 11.0 [9.0,13.5] 443 274 61.9 35.4 [26.9,46.6] RMP susceptible, INH resistant 723 142 19.6 1.1 [0.9,1.4] 629 48 7.6 1.8 [1.3,2.6]
- 15 INH or H: isoniazid; RMP or R: rifampicin; E: ethambutol; S: streptomycin; T: thioacetazone; Z: pyrazinamide; OR: odds ratio
- 16 Preceding numbers in regimens are months of treatment; subscript numbers indicate intermittent number of doses of preceding drug per week
- 17 Level of significance:
- 18 ** p<0.01;
- 19 *** p<0.001
- 20
† programmatically adverse: either failure, relapse, death or LTFU - 21
‡ bacteriologically adverse: either failure or relapse - 22
§ either 2(3 )EHRZ/4H3 R3 , 2(3 )EHRZ/4HR, or 2EHRh Z/4HRh
In 13.6% (52/382) of patients with Hr/Rs TB on phenotypic DST, genotypic DST showed Rr a posteriori (Table 4). Initial Rr was missed in 4.5% (1/22) of new patients tested. Initial Rr was missed more frequently after a bacteriologically unsuccessful Category 2 than after unsuccessful 6-month RMP treatment (36.1% vs 7.4%; aOR 6.8; 95%CI 3.3–13.8). Initial Rr was also missed more frequently with poly-Hr than mono-Hr (15.9% vs. 10.9%), without reaching statistical significance.
Graph
Table 4 Missed initial rifampicin resistance, among 382 patients with initial rifampicin-susceptible/isoniazid-resistant TB on phenotypic DST.
Total Initial Rs confirmed Initial Rr missed N N % N % OR [95%CI] aOR [95%CI] All 382 330 86.4 52 13.6 NA NA INH resistance profile 382 INH mono-resistance 174 155 89.1 19 10.9 1 1 INH poly-resistance 208 175 84.1 33 15.9 1.5 [0.8,2.8] 1.5 [0.8,2.8] Criteria for referral for sequencing Random selection 210 194 92.4 16 7.6 1 1 Presumptive Rr-TB 172 136 79.1 36 20.9 3.2 [1.7,6.0] 3.2 [1.6,6.2] Treatment history First TB episode 22 21 95.5 1 4.5 0.6 [0.1,4.7] 1.1 [0.1,9.5] Failure or relapse of a first treatment 231 214 92.6 17 7.4 1 [1.0,1.0] 1 Failure or relapse of a retreatment 72 46 63.9 26 36.1 7.1 [3.6,14.2] 6.8 [3.3,13.8] Other 57 49 86 8 14 2.1 [0.8,5.0] 2.3 [0.9,5.7]
- 23 INH: Isoniazid; Rr-TB: rifampicin-resistant TB; Rs: rifampicin susceptible; N: number; NA: not applicable; OR: odds ratio; aOR: adjusted odds ratio
- 24
† Multiple samples per episode possible - 25
‡ Other: includes unknown antecedents, non-conform regimens and all lost to follow-up - 26
$ , highly unusual resistance profiles, Rs failures of RMP-throughout regimens, new cases contacts of Rr TB - 27 Level of significance:
- 28 *** p<0.001
Of 242 Rs-TB patients with a bacteriologically unsuccessful first-line treatment 23.1% acquired Rr (Table 5). Acquired Rr was found far more frequently after bacteriologically unsuccessful treatment with a 6-month RMP regimen (28.6%; aOR 29.6; 95%CI 3.6–241.5) or Category 2 (31.9%; aOR 26.8; 95%CI:4.9–146.1) than after unsuccessful treatment with 2(
Graph
Table 5 Predictors of acquired rifampicin resistance in 242 treatment failure and relapse patients with initially rifampicin-susceptible TB.
Total with failure or relapse Acquired Rr N % OR † [95%CI] aOR [95%CI] Total 242 56 23.1 NA NA Regimen during which Rr was acquired 2(3)EHRZ/6HT 68 1 1.5 1 1 6-month RMP-throughout regimen 14 4 28.6 19.3 [2.7,136.8] 29.6 [3.6,241.5] 2SEHRZ/1(2)EHRZ/5EHR 160 51 31.9 21.2 [4.1,110.4] 26.8 [4.9,146.1] Resistance pattern before Rr was acquired Susceptible to INH and RMP 155 19 12.3 1 1 INH mono-resistance 41 12 29.3 3.0 [1.3,6.7] 3.5 [1.5,8.5] INH poly-resistance 45 24 53.3 8.0 [3.8,16.9] 10.2 [4.4,23.7]
- 29 INH or H: isoniazid; RMP or R: rifampicin; E: ethambutol; S: streptomycin; T: thioacetazone; Z: pyrazinamide; N: number; OR: odds ratio, aOR: adjusted odds ratio; Rr: rifampicin resistance
- 30 Preceding numbers in regimens are months of treatment; subscript numbers indicate intermittent number of doses of preceding drug per week
- 31
† To account for the effect of rare events Firth logistic regression method was used - 32
‡ either 2(3 )EHRZ/4H3 R3 , 2(3 )EHRZ/4HR, or 2EHRh Z/4HRh - 33
§ results not shown for one patient with INH resistance, unknown for EMB and SM - 34 Level of significance:
- 35 ** p<0.01;
- 36 *** p<0.001
Mono-Hr vs. Hs/Rs-TB (aOR 3.5; 95%CI 1.5–8.5) and particularly poly-Hr (aOR 10.2; 95%CI: 4.4–23.7) were associated with acquired Rr after recurrence. All four with acquired Rr after 6M-RMP were MDR contacts, 3 out of the 5 with poly-Hr (for a total of 11 Hr contacts on this regimen): one Hs/Rs-TB patient acquired mono-Rr and relapsed and three with initially poly-Hr/Rs TB (1 HS, 2 EHSZ resistant) on deep sequencing acquired Rr after treatment failure.
We used the published data from Georgia as an external dataset to determine comparatively the impact of missed RMP resistance in a high-MDR setting.
Table 6 shows the effect of missed Rr among smear-positive pulmonary TB patients with Hr-TB treated with a first-line regimen in Georgia (higher Rr prevalence) and Bangladesh (lower Rr prevalence). Assuming 8% of missed Rr among "Hr" in both settings, of which half had already been corrected for the Bangladesh outcome analyses, we estimate that 72.2% (6.5/9.0) of treatment failures were due to missed initial Rr in Georgia, against 51.3% (2/3.9) in Bangladesh. In both settings, true Hr/Rs-TB would cause 2–3 failures per 1000 TB patients, new Category 1 and retreatment Category 2 combined at a 730/270 ratio (as in the Georgia publication).
Graph
Table 6 Effect of missed rifampicin resistance on treatment outcomes in patients with isoniazid resistance treated with a first-line regimen, in a setting with high (21%, Georgia) and low (13%, Bangladesh) rifampicin resistance prevalence (combined, new and retreatment cases together at the same proportions).
Initial RMP/INH resistance pattern Bangladesh Georgia No per 1000 cases Hs/Rs-TB 802.0 690.0 Failure in Hs/Rs-TB (2.2%) 18.0 15.0 Rr-TB 130.0 210 Failure in Rr-TB (if treated with a RMP-throughout regimen; 36%) 47.0 75.6 Hr/Rs-TB 62.3 82.0 Failure in Hr/Rs-TB (3.4%) 1.9 2.5 Hr-TB with missed Rr 5.7 18.0 Failure in Hr-TB with missed Rr (36%) 2.0 6.5
37 Hr: Isoniazid-resistant; Hs: isoniazid-susceptible Rr: rifampicin-resistant; Rs: rifampicin-susceptible
In our setting, the 6-month RMP Category 1 regimen was equally successful for susceptible and Hr/Rs-TB patients. In contrast, this was not the case with the predecessor Category 1 8-month 2(
Our findings show better outcomes than those reported by a 2017 meta-analysis, which had shown 21% and 11% bacteriologically adverse outcomes after a 6-month RMP-based Category 1 and Category 2 regimen for Hr/Rs-TB respectively.[[
Rr caused by mutations with lower level resistance and/or fitness loss frequently escapes phenotypic DST, particularly with rapid methods such as the MGIT system.[[
The proportion of missed Rr among those with treatment failure is higher when the prevalence of MDR-TB is higher, because of the similar frequency of easily missed low-level resistance types (as a group) among all rpoB mutations.[[
Missed Rr can have major implications. Based on the 2018 meta-analysis,[[
A safer and more feasible alternative than testing for Hr and using the WHO recommended levofloxacin-strengthened regimen in those with Hr-TB might be the use of the 6-month EHRZ regimen giving INH throughout (6EHRZ, rather than 6E(H)RZ)[[
Acquired Rr is thought to be relatively rare after unsuccessful treatment with the standard 6-month RMP-throughout regimen. However, among recurrent cases after Category 1 and Category 2 treatment acquired Rr was far higher than after the 8-month 2(
Strikingly, all four patients documented with acquired Rr after the 6-month RMP-based regimen were contacts of MDR cases. Two had initial EHSZ resistance, de facto leading to RMP monotherapy. But it is also not unreasonable to assume that these contacts testing Rs were infected by a strain with an increased proportion of naturally resistant mutants, escaping detection despite using advanced molecular techniques. A very low proportion of resistant mutants (between 1/100 and the naturally occurring rpoB mutation rate of 1/10
Our study has some limitations, particularly the passive follow-up of relapse without systematic follow-up assessment of cured patients, though exceptional efforts were made to capture and register incident relapses as a periodical update of the original records in the individual treatment database. The large majority of studies included in the 2017 meta-analysis equally suffered from this limitation, the effect being likely larger in the observational studies with generally larger participant numbers than in the few included clinical trials. Our dataset actually contains patients enrolled in a clinical trial who had a 12-month post-cure follow-up with complete clinical and bacteriologic assessment.[[
Another limitation is our inability to distinguish between true relapse and reinfection or true acquired Rr and superinfection with an Rr-TB strain because we could not confirm strain identity by fingerprinting to exclude reinfection. We therefore pragmatically chose to not declare relapse if the recurrent episode was diagnosed more than 2 years after the treatment completion of the previous episode.
We used microscopy-based definitions for failure and relapse. After the introduction of fluorescence microscopy the demonstration of rare AFB in sputum smears increased.[[
Contact patients of Rr-TB patients were virtually the only previously untreated cases with DST between the surveys and studies included in the analyses of the 6-month RMP-based regimens. The very small number of Hr/Rs among them may not have biased the 6-month RMP regimen outcome analysis. Since they were exclusively responsible for acquired Rr after this regimen, our reported frequency of acquired resistance for the 6-month RMP-based regimen is likely overestimated.
Finally, social, behavioural and other individual data were not recorded in the clinics or on the treatment cards and could thus also not be captured in the databases. In this Muslim country, alcohol consumption is very rare outside tribal minorities, while cigarette smoking is very frequent among males. HIV is virtually absent among TB patients, as shown by ad hoc surveys in the capital but also among the Damien Foundation patients (about 1/1000). Apart from smoking, most likely there has been minimal interference with our findings by these non-quantified factors.
Strengths of our study include the harmonized outcome definitions across cohorts with multiple treatment regimens, and more rigorous phenotypic and genotypic DST that allows robust classification of Hr/Rs versus Hr/Rr.
Our findings contrast with those from the 2017 meta-analysis. [[
Our study confirms that Rr, missed initially or acquired during an RMP-throughout regimen, is by far the most important predictor of first-line recurrence. It accounted for more than half of bacteriologically adverse outcomes among all Rr-TB patients treated with any first-line regimen. To detect both missed initial Rr and acquired Rr we recommend repeating RMP DST after 1 or 2 months treatment in groups at risk, such as previously treated patients, MDR-TB contacts, and those with poly-Hr. Only molecular techniques should be relied upon for ruling out Rr as a condition to prescribe regimens for Hr-TB, even if Rr can still be missed, particularly because of Rr heteroresistance,[[
The 8-month regimen with RMP only in the intensive phase was inadequate for Hr/Rs-TB. Replacing it with RMP-throughout regimens has overcome this inadequacy. However, with the widespread use of RMP-throughout regimens RMP resistance has evolved into a new global problem that couldn't be overcome until highly effective fluoroquinolone-based regimens had been developed.[[
We thank the study participants and staff of Damien Foundation Bangladesh.
By Armand Van Deun; Tom Decroo; Aung Kya Jai Maug; Mohamed Anwar Hossain; Murid Gumusboga; Wim Mulders; Nimer Ortuño-Gutiérrez; Lutgarde Lynen; Bouke C. de Jong and Hans L. Rieder
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