Drug-resistant tuberculosis clinical trials: proposed core research definitions in adults

Drug-resistant tuberculosis (DR-TB) is a growing public health problem, and for the first time in decades, new drugs for the treatment of this disease have been developed. These new drugs have prompted strengthened efforts in DR-TB clinical trials research, and there are now multiple ongoing and planned DR-TB clinical trials. To facilitate comparability and maximise policy impact, a common set of core research definitions is needed, and this paper presents a core set of efficacy and safety definitions as well as other important considerations in DR-TB clinical trials work. To elaborate these definitions, a search of clinical trials registries, published manuscripts and conference proceedings was undertaken to identify groups conducting trials of new regimens for the treatment of DR-TB. Individuals from these groups developed the core set of definitions presented here. Further work is needed to validate and assess the utility of these definitions but they represent an important first step to ensure there is comparability in clinical trials on multidrug-resistant TB.

Phenotypic and genotypic diversity in a multinational sample of drug-resistant Mycobacterium tuberculosis isolates

OBJECTIVE

To develop and evaluate rapid, molecular-based drug susceptibility testing (DST) for extensively drug-resistant tuberculosis (XDR-TB), we assembled a phenotypically and genotypically diverse collection of Mycobacterium tuberculosis isolates from patients evaluated for drug resistance in four high-burden countries.

METHODS

M. tuberculosis isolates from India (n = 111), Moldova (n = 90), the Philippines (n = 96), and South Africa (n = 103) were selected from existing regional and national repositories to maximize phenotypic diversity for resistance to isoniazid, rifampin (RMP), moxifloxacin, ofloxacin, amikacin, kanamycin, and capreomycin. MGIT™ 960 was performed on viable isolates in one laboratory using standardized procedures and drug concentrations. Genetic diversity within drug resistance phenotypes was assessed.

RESULTS

Nineteen distinct phenotypes were observed among 400 isolates with complete DST results. Diversity was greatest in the Philippines (14 phenotypes), and least in South Africa (9 phenotypes). Nearly all phenotypes included multiple genotypes. All sites provided isolates resistant to injectables but susceptible to fluoroquinolones. Many patients were taking drugs to which their disease was resistant.

DISCUSSION

Diverse phenotypes for XDR-TB-defining drugs, including resistance to fluoroquinolones and/or injectable drugs in RMP-susceptible isolates, indicate that RMP susceptibility does not ensure effectiveness of a standard four-drug regimen. Rapid, low-cost DST assays for first- and second-line drugs are thus needed.

Second-line drug susceptibility breakpoints for Mycobacterium tuberculosis using the MODS assay

OBJECTIVE

To establish breakpoint concentrations for the fluoroquinolones (moxifloxacin [MFX] and ofloxacin [OFX]) and injectable second-line drugs (amikacin [AMK], kanamycin [KM] and capreomycin [CPM]) using the microscopic observation drug susceptibility (MODS) assay.

SETTING

A multinational study conducted between February 2011 and August 2012 in Peru, India, Moldova and South Africa.

DESIGN

In the first phase, breakpoints for the fluoroquinolones and injectable second-line drugs (n = 58) were determined. In the second phase, MODS second-line drug susceptibility testing (DST) as an indirect test was compared to MGIT™ DST (n = 89). In the third (n = 30) and fourth (n = 156) phases, we determined the reproducibility and concordance of MODS second-line DST directly from sputum.

RESULTS

Breakpoints for MFX (0.5 μg/ml), OFX (1 μg/ml), AMK (2 μg/ml), KM (5 μg/ml) and CPM (2.5 μg/ml) were determined. In all phases, MODS results were highly concordant with MGIT DST. The few discrepancies suggest that the MODS breakpoint concentrations for some drugs may be too low.

CONCLUSION

MODS second-line DST yielded comparable results to MGIT second-line DST, and is thus a promising alternative. Further studies are needed to confirm the accuracy of the drug breakpoints and the reliability of MODS second-line DST as a direct test.

Relapse more common than reinfection in recurrent tuberculosis 1-2 years post treatment in urban Uganda

OBJECTIVE

To determine the proportion of recurrent tuberculosis (TB) due to relapse with the patient's initial strain or reinfection with a new strain of Mycobacterium tuberculosis 1-2 years after anti-tuberculosis treatment in Uganda, a sub-Saharan TB-endemic country.

DESIGN

Records of patients with culture-confirmed TB who completed treatment at an urban Ugandan clinic were reviewed. Restriction fragment length polymorphism (RFLP) patterns were used to determine relapse or reinfection. Associations between human immunodeficiency virus (HIV) positivity and type of TB recurrence were determined.

RESULTS

Of 1701 patients cured of their initial TB episode with a median follow-up of 1.24 years, 171 (10%) had TB recurrence (8.4 per 100 person-years). Rate and risk factors for recurrence were similar to other studies from sub-Saharan Africa. Insertion sequence (IS) 6110-based RFLP of paired isolates from 98 recurrences identified 80 relapses and 18 reinfections. Relapses among HIV-positive and -negative patients were respectively 79% and 85% of recurrences.

CONCLUSIONS

Relapse was more common and presented earlier than reinfection in both HIV-positive and -negative TB patients 1-2 years after completing treatment. These findings impact both the choice of retreatment drug regimen, as relapsing patients are at higher risk for acquired drug resistance, and clinical trials of new TB regimens with relapse as clinical endpoint.

Comparison of two concentrations of NALC-NaOH for decontamination of sputum for mycobacterial culture

This study compared the effect of using two different concentrations of sodium hydroxide (NaOH) in the N-acetyl-L-cysteine-sodium hydroxide (NALC-NaOH) method for sputum decontamination on smear and culture positivity and the proportion of contaminated cultures: 14% of cultures were contaminated using the standard final 1% NaOH concentration during processing compared to 11% contaminated cultures using a final 1.25% NaOH concentration (P < 0.008). The proportion of cultures positive for mycobacteria decreased from 21% to 11% for sputum processed with 1% and 1.25% final NaOH concentrations, respectively (P < 0.001). Our findings suggest that a small reduction in culture contamination did not justify the considerable loss of positive cultures.

Beijing family Mycobacterium tuberculosis strains differ in their intracellular growth in THP-1 macrophages

SETTING

Previous studies have shown that isolates from cases in IS6110 restriction fragment length polymorphism (RFLP) clusters that have persisted over several years and are widely distributed grow significantly faster in macrophages than isolates from cases with unique RFLP patterns. As members of the Beijing family of Mycobacterium tuberculosis are widely distributed and have been responsible for several large outbreaks, it has been suggested that this genotype may have a selective advantage over other strains.

OBJECTIVE

To determine whether rapid growth in macrophages is a common characteristic of Beijing family strains.

DESIGN

T-helper precursor-1 human macrophages were infected with various Beijing family strains, and intracellular growth and tumor necrosis factor alpha (TNF-alpha) secretion were assessed. Strains differed in their genotype, with IS6110 copy number ranging from 9 to 22.

RESULTS

Strains demonstrated a range of growth phenotypes over the 7-day infection period. Three grew significantly more slowly than the other strains, whereas the fastest growth was observed consistently with isolates of strain 210.

CONCLUSION

Rapid growth in macrophages is not a common characteristic of all Beijing strains. Few Beijing strains are as virulent as strain 210. The growth advantage is consistent with strain 210 having persisted many years in different locations and having caused many outbreaks.

Mycobacterium africanum subtype II is associated with two distinct genotypes and is a major cause of human tuberculosis in Kampala, Uganda

The population structure of 234 Mycobacterium tuberculosis complex strains obtained during 1995 and 1997 from tuberculosis patients living in Kampala, Uganda (East Africa), was analyzed by routine laboratory procedures, spoligotyping, and IS6110 restriction fragment length polymorphism (RFLP) typing. According to biochemical test results, 157 isolates (67%) were classified as M. africanum subtype II (resistant to thiophen-2-carboxylic acid hydrazide), 76 isolates (32%) were classified as M. tuberculosis, and 1 isolate was classified as classical M. bovis. Spoligotyping did not lead to clear differentiation of M. tuberculosis and M. africanum, but all M. africanum subtype II isolates lacked spacers 33 to 36, differentiating them from M. africanum subtype I. Moreover, spoligotyping was not sufficient for differentiation of isolates on the strain level, since 193 (82%) were grouped into clusters. In contrast, in the IS6110-based dendrogram, M. africanum strains were clustered into two closely related strain families (Uganda I and II) and clearly separated from the M. tuberculosis isolates. A further characteristic of both M. africanum subtype II families was the absence of spoligotype spacer 40. All strains of family I also lacked spacer 43. The clustering rate obtained by the combination of spoligotyping and RFLP IS6110 analysis was similar for M. africanum and M. tuberculosis, as 46% and 49% of the respective isolates were grouped into clusters. The results presented demonstrate that M. africanum subtype II isolates from Kampala, Uganda, belong to two closely related genotypes, which may represent unique phylogenetic branches within the M. tuberculosis complex. We conclude that M. africanum subtype II is the main cause of human tuberculosis in Kampala, Uganda.

Safety and bactericidal activity of rifalazil in patients with pulmonary tuberculosis

Rifalazil, also known as KRM-1648 or benzoxazinorifamycin, is a new semisynthetic rifamycin with a long half-life of approximately 60 h. Rifalazil has potent bactericidal activity against Mycobacterium tuberculosis in vitro and in animal models of tuberculosis (TB). Prior studies in healthy volunteers showed that once-weekly doses of 25 to 50 mg of rifalazil were well tolerated. In this randomized, open-label, active-controlled phase II clinical trial, 65 subjects with sputum smear-positive pulmonary TB received one of the following regimens for the first 2 weeks of therapy: 16 subjects received isoniazid (INH) (5 mg/kg of body weight) daily; 16 received INH (5 mg/kg) and rifampin (10 mg/kg) daily; 17 received INH (5 mg/kg) daily plus 10 mg of rifalazil once weekly; and 16 received INH (5 mg/kg) daily and 25 mg of rifalazil once weekly. All subjects were then put on 6 months of standard TB therapy. Pretreatment and day 15 sputum CFU of M. tuberculosis were measured to assess the bactericidal activity of each regimen. The number of drug-related adverse experiences was low and not significantly different among treatment arms. A transient decrease in absolute neutrophil count to less than 2,000 cells/mm(3) was detected in 10 to 20% of patients in the rifalazil- and rifampin-containing treatment arms without clinical consequences. Decreases in CFU counts were comparable among the four treatment arms; however, the CFU results were statistically inconclusive due to the variability in the control arms. Acquired drug resistance did not occur in any patient. Studies focused on determining a maximum tolerated dose will help elucidate the full anti-TB effect of rifalazil.

Inhibition of isoniazid-induced expression of Mycobacterium tuberculosis antigen 85 in sputum: potential surrogate marker in tuberculosis chemotherapy trials

Mycobacterium tuberculosis antigen 85 is induced in vitro by isoniazid (INH); its sustained induction in sputum during tuberculosis (TB) therapy predicts relapse. In this trial, rifampin or rifalazil inhibited the induction of sputum antigen 85 by INH in a dose-dependent fashion. This approach may facilitate the evaluation of new TB drugs.

Predicting the outcome of therapy for pulmonary tuberculosis

Patients vary considerably in their response to treatment of pulmonary tuberculosis. Although several studies have indicated that adverse outcomes are more likely in those patients with delayed sputum sterilization, few tools are available to identify those patients prospectively. In this study, multivariate models were developed to predict the response to therapy in a prospectively recruited cohort of 42 HIV-uninfected subjects with drug-sensitive tuberculosis. The cohort included 2 subjects whose initial response was followed by drug-sensitive relapse. The total duration of culture positivity was best predicted by a model that included sputum M. tuberculosis antigen 85 concentration on Day 14 of therapy, days-to-positive in BACTEC on Day 30, and the baseline radiographic extent of disease (R = 0.63). A model in which quantitative AFB microscopy replaced BACTEC also performed adequately (R = 0.58). Both models predicted delayed clearance of bacilli in both relapses (> 85th percentile of all subjects) using information collected during the first month of therapy. Stratification of patients according to anticipated response to therapy may allow TB treatment to be individualized, potentially offering superior outcomes and greater efficiency in resource utilization, and aiding in the conduct of clinical trials.

Drug tolerance in Mycobacterium tuberculosis

Although Mycobacterium tuberculosis is eradicated rapidly during therapy in some patients with pulmonary tuberculosis, it can persist for many months in others. This study examined the relationship between mycobacterial drug tolerance (delayed killing in vitro), persistence, and relapse. It was performed with 39 fully drug-susceptible isolates from a prospective trial of standard short-course antituberculous therapy with sputum smear-positive, human immunodeficiency virus-uninfected subjects with pulmonary tuberculosis in Brazil and Uganda. The rate of killing in vitro was determined by monitoring the growth index (GI) in BACTEC 12B medium after addition of drug to established cultures and was measured as the number of days required for 99% sterilization. Drugs differed significantly in bactericidal activity, in the following order from greatest to least, rifampin > isoniazid-ethambutol > ethambutol (P < 0.001). Isolates from subjects who had relapses (n = 2) or in whom persistence was prolonged (n = 1) were significantly more tolerant of isoniazid-ethambutol and rifampin than isolates from other subjects (P < 0.01). More generally, the duration of persistence during therapy was predicted by strain tolerance to isoniazid and rifampin (P = 0.012 and 0.026, respectively). Tolerance to isoniazid-ethambutol and tolerance to rifampin were highly correlated (P < 0.001). Tolerant isolates did not differ from others with respect to the MIC of isoniazid; the rate of killing of a tolerant isolate by isoniazid-ethambutol was not increased at higher drug concentrations. These observations suggest that tolerance may not be due to drug-specific mechanisms. Tolerance was of the phenotypic type, although increased tolerance appeared to emerge after prolonged drug exposure in vivo. This study suggests that drug tolerance may be an important determinant of the outcome of therapy for tuberculosis.

Induction of the antigen 85 complex of Mycobacterium tuberculosis in sputum: a determinant of outcome in pulmonary tuberculosis treatment

Sputum quantitative culture, acid-fast smear, days-to-positive by BACTEC, and Mycobacterium tuberculosis antigen 85 complex were monitored during therapy in 42 patients with pulmonary tuberculosis (TB). By BACTEC, 4 patients were persistently positive on days 90-180, and treatment ultimately failed in 2 of these. Antigen 85 expression increased in subjects in whom disease persisted (persisters) from days 0 to 14 when the difference between persisters and nonpersisters was statistically significant (P = .002). Only antigen 85 complex values at day 14 suggested TB persistence at or after day 90. All subjects with day 14 antigen 85 complex values < 60 pg/mL responded rapidly to treatment and were cured. Of those with values > 60 pg/mL, in 33% TB persisted at or after day 90 and treatment failed in 17%. Biologic factors expressed early in therapy, not related to compliance or resistance, may exert a substantial influence on outcome. The antigen 85 complex is critical in cell wall biosynthesis and is induced by isoniazid in vitro. Its induction may represent an adaptive transition to a persistent state during therapy.

Differences in the prevalence of IS6110 insertion sites in Mycobacterium tuberculosis strains: low and high copy number of IS6110

SETTING

Mycobacterium tuberculosis (M. tuberculosis) isolates from various parts of the USA which have few copies of the insertion sequence IS6110.

OBJECTIVES

To characterize the sites of insertion of IS6110 among M. tuberculosis isolates that have one to six copies of the insertion sequence.

DESIGN

The mixed-linker polymerase chain reaction (ML-PCR) procedure was used to amplify the terminal repeats on the ends of IS6110 and adjacent flanking sequences. From the ML-PCR products, sequences flanking 14 copies of IS6110 in strains containing less than seven copies of the insertion were determined. Sequence information from the flanking deoxyribonucleic acid was used to construct flanking primers that can be used to indicate the presence of IS6110 at a particular site when paired with outbound IS6110 primers in a PCR. Over 200 strains of diverse origin were screened for the insertion of IS6110 at several distinct sites using this procedure.

RESULTS

The direct repeat (DR) locus has been described as a highly preferred site for insertion of IS6110 in strains of M. tuberculosis. Another highly preferred site of insertion of IS6100, DK1, is herein described. Insertions at DK1 are highly prevalent in M. tuberculosis strains harboring two to six copies of IS6110. The prevalence of insertions at this site decreases in strains with more than six copies of IS6110, even though the sequence itself is present in strains lacking a copy of IS6110 at this site.

CONCLUSION

In addition to the DR locus there are other conserved sites of insertion among M. tuberculosis strains. The data further suggest a separate lineage for the high copy and the low copy strains, and a possible sequential insertion of IS6110 in strains of M. tuberculosis with less than seven copies.

Detection of Mycobacterium tuberculosis in clinical specimens from children using a polymerase chain reaction

OBJECTIVE

We evaluated the usefulness of the polymerase chain reaction (PCR) using the insertion sequence IS6110 as the target for DNA to detect Mycobacterium tuberculosis in clinical specimens from children.

STUDY DESIGN

This was a prospective, controlled, blinded study comparing PCR on clinical specimens, mycobacterial culture, and clinical diagnosis.

PATIENTS

Sixty-five hospitalized children were evaluated, 35 with tuberculosis disease and 30 controls. Cases were defined by culture and/or specific clinical criteria. Controls included patients with tuberculosis infection but no detectable disease as well as patients free of tuberculosis infection and disease.

RESULTS

Polymerase chain reaction had a sensitivity of 40% and a specificity of 80% compared with clinical diagnosis. Mycobacterial culture had a sensitivity of 37%. The combination of culture and PCR identified 19 of 35 children (54%) with clinically diagnosed tuberculosis. There were six children with false-positive PCR results: One had tuberculosis infection without disease, two had Mycobacterium avium lymphadenitis, and three had diagnoses unrelated to tuberculosis.

CONCLUSIONS

The sensitivity of PCR is comparable to that of culture for detecting M tuberculosis in children, and may strengthen and hasten the clinical diagnosis in culture-negative patients. However, because of the limitations in specificity, the results of PCR alone are insufficient to diagnose tuberculosis in children. Although ongoing refinements in PCR techniques should improve the specificity of this test, epidemiologic and clinical information continue to be the most important consideration in the diagnosis of tuberculosis in culture-negative children.

Characterization of rifampin-resistance in pathogenic mycobacteria

The emergence of rifampin-resistant strains of pathogenic mycobacteria has threatened the usefulness of this drug in treating mycobacterial diseases. Critical to the treatment of individuals infected with resistant strains is the rapid identification of these strains directly from clinical specimens. It has been shown that resistance to rifampin in Mycobacterium tuberculosis and Mycobacterium leprae apparently involves mutations in the rpoB gene encoding the beta-subunit of the RNA polymerases of these species. DNA sequences were obtained from a 305-bp fragment of the rpoB gene from 110 rifampin-resistant and 10 rifampin-susceptible strains of M. tuberculosis from diverse geographical regions throughout the world. In 102 of 110 rifampin-resistant strains 16 mutations affecting 13 amino acids were observed. No mutations were observed in rifampin-susceptible strains. No association was found between particular mutations in the rpoB gene and drug susceptibility patterns of multidrug-resistant M. tuberculosis strains. Drug-resistant M. tuberculosis strains from the same outbreak and exhibiting the same IS6110 DNA fingerprint and drug susceptibility pattern contained the same mutation in the rpoB gene. However, mutations are not correlated with IS6110 profiling outside of epidemics. The evolution of rifampin resistance as a consequence of mutations in the rpoB gene was documented in a patient who developed rifampin resistance during the course of treatment. Rifampin-resistant strains of M. leprae, Mycobacterium avium, and Mycobacterium africanum contained mutations in the rpoB gene similar to that documented for M. tuberculosis. This information served as the basis for developing a rapid DNA diagnostic assay (PCR-heteroduplex formation) for the detection of rifampin susceptibility of M. tuberculosis.

Pediatric blood culture evaluation of the BACTEC PEDS Plus and the DuPont Isolator 1.5 systems

A new nonradiometric BACTEC medium has been developed for culturing pediatric blood samples. The BACTEC PEDS Plus medium (BACTEC PED) consists of 20 ml of an enriched broth with resins. In contrast to the other aerobic BACTEC media, there is a lower concentration of sodium polyanetholesulfonate in the medium and more CO2 in the headspace of the vial. This study was conducted in two different pediatric settings to compare the performance of the BACTEC PED medium with the Du Pont Isolator 1.5 system (ISO 1.5) in terms of overall organism recovery and time to detection. Equal volumes of up to 1.5 ml were tested in both systems. A total of 4063 culture sets were analyzed, yielding 301 (7.4%) clinically significant isolates. Of these, 86 (29%) were recovered only from the BACTEC PED and 12 (4%) only from the ISO 1.5 (p less than 0.001). BACTEC PED recovered significantly more staphylococci and Enterobacteriaceae than ISO 1.5 (p less than 0.001 and p less than 0.005, respectively). Detection times of isolates recovered in both systems were comparable. For those patients on antibiotic therapy at the time of culture, 21 (37%) were positive only in the BACTEC PED, whereas two (4%) were positive only in the ISO 1.5. The nontherapy group had 61 (27%) organisms that were detected in BACTEC PED only and 9 (4%) in ISO 1.5 only. These results indicate that BACTEC PED is a significant advance in blood culture systems that will provide a sensitive method for detecting pediatric bacteremias.

Evaluation of the Phadebact CSF test for detection of the four most common causes of bacterial meningitis

A five-center collaborative study was undertaken to determine the suitability of the Phadebact CSF test kit and the Phadebact group B Streptococcus reagent for routine use by clinical laboratories to detect antigens of common organisms causing bacterial meningitis. The kits employ staphylococcal protein A coagglutination to detect the antigens of Haemophilus influenzae types a, b, c, d, e, and f, Neisseria meningitidis groups A, B, C, Y, and W135, Streptococcus pneumoniae (83 serotypes), and group B Streptococcus. A total of 2,817 individual tests were performed on 577 cerebrospinal fluid specimens. The percent positive specimens detected by coagglutination was as follows: overall, 84%; H. influenzae, 97%; group B Streptococcus, 75%; S. pneumoniae, 71%; and N. meningitidis, 58%. Eighty-five of the specimens were also tested by counterimmunoelectrophoresis. Coagglutination was more sensitive than counterimmunoelectrophoresis because it detected 74% of the positive specimens, whereas counterimmunoelectrophoresis detected only 65%. No false-positive results were obtained with coagglutination. The Phadebact CSF test kit is recommended for routine use in screening cerebrospinal fluid samples for antigens of the common organisms causing bacterial meningitis along with the Gram stain and culture for delayed confirmation of the rapid results.