The thin-layer agar method for direct phenotypic detection of multi- and extensively drug-resistant tuberculosis.

BACKGROUND: Molecular techniques rapidly detect resistance to rifampicin (RMP) and isoniazid (INH), but do not eliminate the need for culture-based drug susceptibility testing (DST) against other drugs. The thin-layer agar (TLA) test, a non-commercial direct DST method, has demonstrated good performance for INH and RMP; however, evidence is still limited, and its applicability for DST of ofloxacin (OFX) and kanamycin (KM) is unknown. DESIGN: We compared 279 TLA DST results with those of MGIT for INH and RMP, and 280 results for OFX and KM with those of the 7H11 agar proportion method, obtained from 320 smear-positive samples from 165 Georgian TB patients. Discrepancies were solved by comparison with a composite reference standard. The prevalence of multidrug-resistant tuberculosis (TB) was 30 of 164 patients (18.3%), 2 (6.7%) of whom had extensively drug-resistant TB. RESULTS: TLA showed 94.7%, 98.2%, 100% and 78.9% sensitivity, respectively, for INH, RMP, OFX and KM, with 100% specificity. Average time to results was 7 days in TLA, 23 in MGIT and 49 for 7H11 agar. CONCLUSIONS: In low-resource settings, TLA can be applied for the rapid detection of resistance to INH, RMP and fluoroquinolones. Further studies are necessary to improve sensitivity to KM and further assess its performance for OFX and other drugs and its applicability in field conditions.

The potential of a multiplex high-throughput molecular assay for early detection of first and second line tuberculosis drug resistance mutations to improve infection control and reduce costs: a decision analytical modeling study.

BACKGROUND: Molecular resistance detection (MRD) of resistance to second-line anti-tuberculous drugs provides faster results than phenotypic tests, may shorten treatment and allow earlier separation among patients with and without second-line drug resistance. METHODS: In a decision-analytical model we simulated a cohort of patients diagnosed with TB in a setting where drug resistant TB is highly prevalent and requires initial hospitalization, to explore the potential benefits of a high-throughput MRD-assay for reducing potential nosocomial transmission of highly resistant strains, and total costs for diagnosis of drug resistance, treatment and hospitalization. In the base case scenario first-line drug resistance was diagnosed with WHO-endorsed molecular tests, and second-line drug resistance with culture and phenotypic methods. Three alternative scenarios were explored, each deploying high-throughput MRD allowing either detection of second-line mutations in cultured isolates, directly on sputum, or MRD with optimized markers. RESULTS: Compared to a base case scenario, deployment of high-throughput MRD reduced total costs by 17-21 %. The period during which nosocomial transmission may take place increased by 15 % compared to the base case if MRD had currently reported suboptimal sensitivity and required cultured isolates; increased by 7 % if direct sputum analysis were possible including in patients with smear-negative TB, and reduced by 24 % if the assay had improved markers, but was still performed on cultured isolates. Improved clinical sensitivity of the assay (additional markers) by more than 35 % would be needed to avoid compromising infection control. CONCLUSIONS: Further development of rapid second-line resistance testing should prioritize investment in optimizing markers above investments in a platform for direct analysis of sputum.

Prevalence and risk factors for multidrug-resistant tuberculosis in the Republic of Georgia: a population-based study.

SETTING: Multidrug-resistant tuberculosis (MDR-TB, defined as resistance to at least isoniazid and rifampicin) has emerged as a serious global public health problem, especially in the former Soviet republics. The extent of the problem in Georgia has been incompletely defined. OBJECTIVE: To determine the prevalence and risk factors for MDR-TB in Georgia. DESIGN: A population-based study was carried out between July 2005 and May 2006. RESULTS: Of 1314 patients with acid-fast bacilli smear- and culture-positive pulmonary tuberculosis (TB), 799 (60.8%) were newly diagnosed patients and 515 (39.2%) had been treated previously. Overall, 733 (56%) patients had resistance to at least one anti-tuberculosis drug and 195 (15%) had MDR-TB. Patients who had been treated previously for TB were significantly more likely to have MDR-TB than newly diagnosed patients (141/515 [27.4%] vs. 54/794 [6.8%], OR 5.27, 95%CI 3.75-7.41). In multivariate analysis, previous TB treatment (aOR 5.47, 95%CI 3.87-7.74) and female sex (aOR1.58, 95%CI 1.02-2.32) were independent risk factors for the presence of MDR-TB. CONCLUSIONS: Drug-resistant TB, including MDR-TB, has emerged as a major public health problem in Georgia. Further TB control efforts need to be implemented to prevent the development of new cases of MDR-TB and to treat existing patients with MDR-TB.