Use Of Drug Susceptibility Testing Research Articles

Surveillance for TB drug resistance using routine rapid diagnostic testing data: Methodological development and application in Brazil

Effectively responding to drug-resistant tuberculosis (TB) requires accurate and timely information on resistance levels and trends. In contexts where use of drug susceptibility testing has not been universal (i.e. not all patients are offered testing), surveillance for rifampicin-resistance—one of the core drugs in the TB treatment regimen—has relied on resource-intensive and infrequent nationally-representative prevalence surveys. The expanded availability of rapid diagnostic tests (RDTs) over the past decade has increased testing coverage in many settings. However, RDT data collected in the course of routine (but not universal) use may provide biased estimates of resistance if the subset of patients receiving RDTs is not representative of the overall cohort. Here, we developed a method that attempts to correct for non-random use of RDT testing in the context of routine TB diagnosis to recover unbiased estimates of resistance among new and previously treated TB cases. Specifically, we employed statistical corrections to model rifampicin resistance among TB notifications with observed Xpert MTB/RIF (a WHO-recommended RDT) results using a hierarchical generalized additive regression model, and then used model output to impute results for untested individuals. We applied this model to 2017–2023 case-level data on over 800,000 patients from Brazil. Modeled estimates of the prevalence of rifampicin resistance were substantially higher than naïve estimates, with estimated prevalence ranging between 28–44% higher for new cases and 2–17% higher for previously treated cases. Our estimates of RR-TB incidence were estimated with narrower uncertainty intervals relative to WHO estimates for the same time period, and were robust to alternative model specifications. Our approach provides a generalizable method to leverage routine RDT data to derive timely estimates of RR-TB prevalence among notified TB cases in settings where testing for TB drug resistance is not universal.

Of Testing and Treatment: Implications of Implementing New Regimens for Multidrug-Resistant Tuberculosis.

A novel, shorter-course regimen for treating multidrug-resistant (MDR) tuberculosis was recently recommended by the World Health Organization. However, the most appropriate use of drug susceptibility testing (DST) to support this regimen is less clear. Implementing countries must therefore often choose between using a standardized regimen despite high levels of underlying drug resistance or require more stringent DST prior to treatment initiation. The former carries a high likelihood of exposing patients to de facto monotherapy with a critical drug class (fluoroquinolones), whereas the latter could exclude large groups of patients from their most effective treatment option. We discuss the implications of this dilemma and argue for an approach that will integrate DST into the delivery of any novel antimicrobial regimen, without excessively stringent requirements. Such guidance could make the novel MDR tuberculosis regimen available to most patients while reducing the risk of generating additional drug resistance.

Risk factors for poor multidrug-resistant tuberculosis treatment outcomes in Kyiv Oblast, Ukraine

BackgroundUkraine is among ten countries with the highest burden of multidrug- resistant TB (MDR-TB) worldwide. Treatment success rates for MDR-TB in Ukraine remain below global success rates as reported by the World Health Organization. Few studies have evaluated predictors of poor MDR-TB outcomes in Ukraine.MethodsWe conducted a retrospective analysis of patients initiated on MDR-TB treatment in the Kyiv Oblast of Ukraine between January 01, 2012 and March 31st, 2015. We defined good treatment outcomes as cure or completion and categorized poor outcomes among those who died, failed treatment or defaulted. We used logistic regression analyses to identify baseline patient characteristics associated with poor MDR-TB treatment outcomes.ResultsAmong 360 patients, 65 (18.1%) achieved treatment cure or completion while 131 (36.4%) died, 115 (31.9%) defaulted, and 37 (10.3%) failed treatment. In the multivariate analysis, the strongest baseline predictors of poor outcomes were HIV infection without anti-retroviral therapy (ART) initiation (aOR 10.07; 95% CI 1.20–84.45; p 0.03) and presence of extensively-drug resistant TB (aOR 9.19; 95% CI 1.17–72.06; p 0.03). HIV-positive patients initiated on ART were not at increased risk of poor outcomes (aOR 1.43; 95% CI 0.58–3.54; p 0.44). There was no statistically significant difference in risk of poor outcomes among patients who received baseline molecular testing with Gene Xpert compared to those who were not tested (aOR 1.31; 95% CI 0.63–2.73).ConclusionsRigorous compliance with national guidelines recommending prompt initiation of ART among HIV/TB co-infected patients and use of drug susceptibility testing results to construct treatment regimens can have a major impact on improving MDR-TB treatment outcomes in Ukraine.

Rationing tests for drug-resistant tuberculosis - who are we prepared to miss?

BackgroundEarly identification of patients with drug-resistant tuberculosis (DR-TB) increases the likelihood of treatment success and interrupts transmission. Resource-constrained settings use risk profiling to ration the use of drug susceptibility testing (DST). Nevertheless, no studies have yet quantified how many patients with DR-TB this strategy will miss.MethodsA total of 1,545 subjects, who presented to Lima health centres with possible TB symptoms, completed a clinic-epidemiological questionnaire and provided sputum samples for TB culture and DST. The proportion of drug resistance in this population was calculated and the data was analysed to demonstrate the effect of rationing tests to patients with multidrug-resistant TB (MDR-TB) risk factors on the number of tests needed and corresponding proportion of missed patients with DR-TB.ResultsOverall, 147/1,545 (9.5 %) subjects had culture-positive TB, of which 32 (21.8 %) had DR-TB (MDR, 13.6 %; isoniazid mono-resistant, 7.5 %; rifampicin mono-resistant, 0.7 %). A total of 553 subjects (35.8 %) reported one or more MDR-TB risk factors; of these, 506 (91.5 %; 95 % CI, 88.9–93.7 %) did not have TB, 32/553 (5.8 %; 95 % CI, 3.4–8.1 %) had drug-susceptible TB, and only 15/553 (2.7 %; 95 % CI, 1.5–4.4 %) had DR-TB. Rationing DST to those with an MDR-TB risk factor would have missed more than half of the DR-TB population (17/32, 53.2 %; 95 % CI, 34.7–70.9).ConclusionsRationing DST based on known MDR-TB risk factors misses an unacceptable proportion of patients with drug-resistance in settings with ongoing DR-TB transmission. Investment in diagnostic services to allow universal DST for people with presumptive TB should be a high priority.

Use of Drug-Susceptibility Testing for Management of Drug-Resistant Tuberculosis, Thailand, 2004–2008

In 2004, routine use of culture and drug-susceptibility testing (DST) was implemented for persons in 5 Thailand provinces with a diagnosis of tuberculosis (TB). To determine if DST results were being used to guide treatment, we conducted a retrospective chart review for patients with rifampin-resistant or multidrug-resistant (MDR) TB during 2004–2008. A total of 208 patients were identified. Median time from clinical sample collection to physician review of DST results was 114 days. Only 5.8% of patients with MDR TB were empirically prescribed an appropriate regimen; an additional 31.3% received an appropriate regimen after DST results were reviewed. Most patients with rifampin -resistant or MDR TB had successful treatment outcomes. Patients with HIV co-infection and patients who were unmarried or had received category II treatment before DST results were reviewed had less successful outcomes. Overall, review of available DST results was delayed, and results were rarely used to improve treatment.

Risk factors for tuberculosis treatment failure, default, or relapse and outcomes of retreatment in Morocco

BackgroundPatients with tuberculosis require retreatment if they fail or default from initial treatment or if they relapse following initial treatment success. Outcomes among patients receiving a standard World Health Organization Category II retreatment regimen are suboptimal, resulting in increased risk of morbidity, drug resistance, and transmission.. In this study, we evaluated the risk factors for initial treatment failure, default, or early relapse leading to the need for tuberculosis retreatment in Morocco. We also assessed retreatment outcomes and drug susceptibility testing use for retreatment patients in urban centers in Morocco, where tuberculosis incidence is stubbornly high.MethodsPatients with smear- or culture-positive pulmonary tuberculosis presenting for retreatment were identified using clinic registries in nine urban public clinics in Morocco. Demographic and outcomes data were collected from clinical charts and reference laboratories. To identify factors that had put these individuals at risk for failure, default, or early relapse in the first place, initial treatment records were also abstracted (if retreatment began within two years of initial treatment), and patient characteristics were compared with controls who successfully completed initial treatment without early relapse.Results291 patients presenting for retreatment were included; 93% received a standard Category II regimen. Retreatment was successful in 74% of relapse patients, 48% of failure patients, and 41% of default patients. 25% of retreatment patients defaulted, higher than previous estimates. Retreatment failure was most common among patients who had failed initial treatment (24%), and default from retreatment was most frequent among patients with initial treatment default (57%). Drug susceptibility testing was performed in only 10% of retreatment patients. Independent risk factors for failure, default, or early relapse after initial treatment included male gender (aOR = 2.29, 95% CI 1.10-4.77), positive sputum smear after 3 months of treatment (OR 7.14, 95% CI 4.04-13.2), and hospitalization (OR 2.09, 95% CI 1.01-4.34). Higher weight at treatment initiation was protective. Male sex, substance use, missed doses, and hospitalization appeared to be risk factors for default, but subgroup analyses were limited by small numbers.ConclusionsOutcomes of retreatment with a Category II regimen are suboptimal and vary by subgroup. Default among patients receiving tuberculosis retreatment is unacceptably high in urban areas in Morocco, and patients who fail initial tuberculosis treatment are at especially high risk of retreatment failure. Strategies to address risk factors for initial treatment default and to identify patients at risk for failure (including expanded use of drug susceptibility testing) are important given suboptimal retreatment outcomes in these groups.

New Challenges in the Clinical Management of Drug-Resistant Tuberculosis

Strains of Mycobacterium tuberculosis are multidrug-resistant when isoniazid and rifampin, the two most powerful antituberculous agents, do not inhibit their growth. Only a decade ago, outbreaks of multidrug-resistant tuberculosis (MDR-TB) occurred in New York, California, and Florida. In each setting, early detection by physicians decreased both transmission of and deaths caused by these strains. Working in Haiti, Peru, and Russia, our team has treated over 1,000 patients sick with MDR-TB. Most infecting strains were resistant to all first-line drugs. Because no new antituberculous drugs have been developed in decades, therapeutic options for such patients are limited. Our own experience suggests, however, that prompt detection and effective therapy can cure the great majority of cases of active MDR-TB. We review below the principles of MDR-TB treatment: 18–24 months of therapy with multidrug regimens, designed with use of drug susceptibility testing, and close attention to the management of adverse effects. We also discuss the treatment of MDR-TB in children, during pregnancy, and in the presence of HIV coinfection. Controversies in the management of MDR-TB are reviewed, including the use of resective surgery, the relative efficacy of different fluoroquinolones, and postexposure prophylaxis for close contacts of patients with pulmonary MDR-TB.