Epidemiology and treatment of multidrug resistant tuberculosis

The burden of drug resistant tuberculosis in a predominantly nomadic population in Uganda: a mixed methods study

Background

Emergence of drug resistant tuberculosis (DR-TB) has aggravated the tuberculosis (TB) public health burden worldwide and especially in low income settings. We present findings from a predominantly nomadic population in Karamoja, Uganda with a high-TB burden (3500 new cases annually) and sought to determine the prevalence, patterns, factors associated with DR-TB.

Methods

We used mixed methods of data collection. We enrolled 6890 participants who were treated for tuberculosis in a programmatic setting between January 2015 and April 2018. A cross sectional study and a matched case control study with conditional logistic regression and robust standard errors respectively were used to the determine prevalence and factors associated with DR-TB. The qualitative methods included focus group discussions, in-depth interviews and key informant interviews.

Results

The overall prevalence of DR-TB was 41/6890 (0.6%) with 4/64,197 (0.1%) among the new and 37/2693 (1.4%) among the previously treated TB patients respectively. The drug resistance patterns observed in the region were mainly rifampicin mono resistant (68.3%) and Multi Drug-Resistant Tuberculosis (31.7%). Factors independently associated with DR-TB were previous TB treatment, adjusted odds ratio (aOR) 13.070 (95%CI 1.552–110.135) and drug stock-outs aOR 0.027 (95%CI 0.002–0.364). The nomadic lifestyle, substance use, congested homesteads and poor health worker attitudes were a great challenge to effective treatment of TB.

Conclusion

Despite having the highest national TB incidence, Karamoja still has a low DR-TB prevalence. Previous TB treatment and drug stock outs were associated with DR-TB. Regular supply of anti TB medications and health education may help to stem the burden of TB disease in this nomadic population.

Bayesian Spatial Survival Analysis of Duration to Cure among New Smear-Positive Pulmonary Tuberculosis (PTB) Patients in Iran, during 2011-2018

Mycobacterium tuberculosis is the causative agent of tuberculosis (TB), and pulmonary TB is the most prevalent form of the disease worldwide. One of the most concrete actions to ensure an effective TB control program is monitoring TB treatment outcomes, particularly duration to cure; but, there is no strong evidence in this respect. Thus, the primary aim of this study was to examine the possible spatial variations of duration to cure and its associated factors in Iran using the Bayesian spatial survival model. All new smear-positive PTB patients have diagnosed from March 2011 to March 2018 were included in the study. Out of 34,744 patients, 27,752 (79.90%) patients cured and 6992 (20.10%) cases were censored. For inferential purposes, the Markov chain Monte Carlo algorithms are applied in a Bayesian framework. According to the Bayesian estimates of the regression parameters in the proposed model, a Bayesian spatial log-logistic model, the variables gender (male vs. female, TR = 1.09), altitude (>750 m vs. ≤750 m, TR = 1.05), bacilli density in initial smear (3+ and 2+ vs. 1–9 Basil & 1+, TR = 1.09 and TR = 1.02, respectively), delayed diagnosis (>3 months vs. <1 month, TR = 1.02), nationality (Iranian vs. other, TR = 1.02), and location (urban vs. rural, TR = 1.02) had a significant influence on prolonging the duration to cure. Indeed, pretreatment weight (TR = 0.99) was substantially associated with shorter duration to cure. In summary, the spatial log-logistic model with convolution prior represented a better performance to analyze the duration to cure of PTB patients. Also, our results provide valuable information on critical determinants of duration to cure. Prolonged duration to cure was observed in provinces with low TB incidence and high average altitude as well. Accordingly, it is essential to pay a special attention to such provinces and monitor them carefully to reduce the duration to cure while maintaining a focus on high-risk provinces in terms of TB prevalence.

An audiological profile of patients infected with multi-drug resistant tuberculosis at a district hospital in KwaZulu-Natal

BACKGROUND

The increased incidence of multi-drug-resistant tuberculosis (MDR-TB) and the consequent use of aminoglycosides with their ototoxic potential necessitate a better understanding of the audiological pattern of infected patients.

OBJECTIVE

To describe the occurrence and nature of hearing loss in patients with MDR-TB receiving aminoglycosides over a period of 6 months.

METHODS

Baseline and five consecutive monthly audiological assessments were conducted on 52 adults at a hospital in KwaZulu-Natal. A longitudinal descriptive study was implemented. A conventional audiological test battery, extended high frequency audiometry and otoacoustic emission testing were conducted. Data were analysed using SPSS version 19 statistical software package.

RESULTS

Decreased hearing was the most common audiological symptom experienced. Bilateral sensorineural hearing loss was predominant. Ototoxic hearing loss was noted in 27 participants (52%) in 1 month post-treatment. Hearing loss progressed from mild to moderate at post-treatment one, to moderate to severe at post-treatment three and severe to profound at post-treatment five. Changes in hearing function were noted in 52 participants (100%) by post-treatment five. High and ultra-high frequencies were most affected. Speech discrimination scores deteriorated over time. The number of patients with absent distortion product otoacoustic emissions increased over treatment duration.

CONCLUSION

The greatest effects were observed in the high frequencies before manifesting in the lower frequencies. This highlights the importance of inclusion of high frequency audiometry in the early detection of ototoxicity which can go undiagnosed with traditional audiometry. The high prevalence of hearing loss has implications for the provision of audiological service to this patient population.

Levels of microRNA miR-16 and miR-155 are altered in serum of patients with tuberculosis and associate with responses to therapy

Identification of blood biomarkers that can be useful for predicting Mycobacterium tuberculosis (M.TB) infection, effect of therapy and Multi Drug Resistant (MDR) TB infected individuals is clinically useful for combating tuberculosis epidemic. In this study, we have evaluated the levels of selected miRNAs in serum of TB and MDR TB patients. In addition, we have studied their levels in serum of patients post-therapy. The levels of 4-miRNAs (miR-16, miR-29a, miR-125b and miR-155) were measured in 30 newly diagnosed TB patients, 19 Multi Drug Resistant (MDR) TB patients, 10 patients who completed TB therapy and were TB negative. 30 healthy individuals were recruited as controls. The levels of the miRNAs were estimated by qRT-PCR. Of the four miRNAs studied, the levels of miR-16 were significantly elevated and miR-155 were significantly reduced in serum of TB patients as compared to uninfected controls. The Receiver Operating Characteristic (ROC) curve of miR-16 and miR-155 exhibited a significant distinguishing efficiency with an AUC value of 1 (95% CI, 1 to 1) and 0.967 (95% CI, 0.92-1.04) respectively. Following the therapy, the levels of miR-16 and miR-155 returned to those observed in healthy subjects. In patients with MDR TB, miR-155 was lower as compared to healthy controls and TB treated group but higher as compared to TB naïve patients. miR-16 levels were lowest in serum of MDR TB patients compared to TB naïve, TB treated group and healthy controls. In conclusion, miR-16 and miR-155 in serum may act as surrogate biomarker for studying TB infection, progression of therapy and MDR TB.

Detection of rpoB gene mutations using helicase-dependent amplification

For patients infected with tuberculosis, detection of rpoB gene mutations is critical for diagnosing drug-resistant strains of the causative pathogen, Mycobacterium tuberculosis (MTB). Traditional approaches to drug resistance include culture, which is very slow. Recently described real-time polymerase chain reaction approaches have addressed turnaround time but at relatively high cost. Here, we describe a novel amplification method, termed blocked-primer helicase-dependent amplification, for amplifying rpoB gene sequences in MTB. Resultant amplicon is hybridized to a probe set arrayed on a modified silicon-based chip to determine if there is any mutation in that region. Using this method, we could detect the majority of clinically relevant mutations in rpoB gene.

Rolling circle amplification for direct detection of rpoB gene mutations in Mycobacterium tuberculosis isolates from clinical specimens

Rapid and accurate detection of multidrug resistance (MDR) in Mycobacterium tuberculosis is essential to improve treatment outcomes and reduce global transmission but remains a challenge. Rifampin (RIF) resistance is a reliable marker of MDR tuberculosis (TB) since by far the majority of RIF-resistant strains are also isoniazid (INH) resistant. We have developed a rapid, sensitive, and specific method for detecting the most common mutations associated with RIF resistance, in the RIF resistance determining region (RRDR) of rpoB, using a cocktail of six padlock probes and rolling circle amplification (RCA). We used this method to test 46 stored M. tuberculosis clinical isolates with known RIF susceptibility profiles (18 RIF resistant, 28 susceptible), a standard susceptible strain (H37Rv, ATCC 27294) and 78 M. tuberculosis culture-positive clinical (sputum) samples, 59 of which grew RIF-resistant strains. All stored clinical isolates were correctly categorized, by the padlock probe/RCA method, as RIF susceptible or resistant; the sensitivity and specificity of the method, for direct detection of phenotypically RIF-resistant M. tuberculosis in clinical specimens, were 96.6 and 89.5%, respectively. This method is rapid, simple, and inexpensive and has the potential for high-throughput routine screening of clinical specimens for MDR M. tuberculosis, particularly in high prevalence settings with limited resources.

Hopelessness as a basis for tuberculosis diagnostic delay in the Arkhangelsk region: a grounded theory study

Background

Data about delayed tuberculosis diagnosis in Northern Russia are scarce yet such knowledge could enhance the care of tuberculosis. The Arkhangelsk region is situated in the north of Russia, where the population is more than one million residents.

The aim of the study was to understand factors influencing diagnostic delay among patients with tuberculosis in the Arkhangelsk region and to develop a theoretical model in order to explain diagnostic delay from the patients’ perspectives.

Methods

Twenty-three patients who had experienced diagnostic delay of tuberculosis were interviewed in Arkhangelsk. Using a qualitative approach, we conducted focus-group discussions for data gathering using Grounded Theory with the Paradigm Model to analyse the phenomenon of diagnostic delay.

Results

The study resulted in a theoretical model of the pathway of delay of tuberculosis diagnosis in the Arkhangelsk region in answer to the question: “Why and how do patients in the Arkhangelsk region delay tuberculosis diagnosis?” The model included categories of causal conditions, context and intervening conditions, action/interaction strategies, and consequences. The causal condition and main concern of the patients was that they were overpowered by hopelessness. Patients blamed policy, the administrative system, and doctors for their unfortunate life circumstances. This was accompanied by avoidance of health care, denial of their own health situations, and self-treatment. Only a deadly threat was a sufficient motivator for some patients to seek medical help. “Being overpowered by hopelessness” was identified as the core category that affected their self-esteem and influenced their entire lives, including family, work and social relations, and appeared even stronger in association with alcohol use. This category reflected the passive position of many patients in this situation, including their feelings of inability to change anything in their lives, to obtain employment, or to qualify for disability benefits.

Conclusion

The main contributing factor to unsuccessful health-seeking behaviour for patients with tuberculosis was identified as “being overpowered by hopelessness.” This should be taken into consideration when creating any preventive programs and diagnostic algorithms aimed at increasing knowledge about TB, improving the health system, decreasing alcohol consumption and reducing the poverty of the people in Arkhangelsk.

Antibiotic resistance: from Darwin to Lederberg to Keynes

The emergence and spread of antibiotic-resistant bacteria reflects both, a gradual, completely Darwinian evolution, which mostly yields slight decreases in antibiotic susceptibility, along with phenotypes that are not precisely characterized as "resistance"; and sudden changes, from full susceptibility to full resistance, which are driven by a vast array of horizontal gene transfer mechanisms. Antibiotics select for more than just antibiotic resistance (i.e., increased virulence and enhanced gene exchange abilities); and many non-antibiotic agents or conditions select for or maintain antibiotic resistance traits as a result of a complex network of underlying and often overlapping mechanisms. Thus, the development of new antibiotics and thoughtful, integrated anti-infective strategies is needed to address the immediate and long-term threat of antibiotic resistance. Since the biology of resistance is complex, these new drugs and strategies will not come from free-market forces, or from "incentives" for pharmaceutical companies.

Impact of rapid drug susceptibility testing for tuberculosis: program experience in Lima, Peru

SETTING

Programmatic implementation of decentralized rapid drug susceptibility testing (DST) in Lima, Peru.

OBJECTIVE

Pre-post analysis compared time to diagnosis, treatment outcome and survival among patients tested with direct nitrate reductase assay (NRA) vs. indirect conventional methods.

DESIGN

From 2005 to 2009, we prospectively followed all patients referred for DST before (control) and after (intervention) NRA implementation. Among those referred for DST, NRA was used for smear-positive samples of patients with no prior history of multidrug resistance or treatment for multidrug-resistant tuberculosis (TB). Data were abstracted from patient charts and laboratory registers. Endpoints were favorable outcomes, time to result and time to death.

RESULTS

Of those patients who met the criteria for NRA, 740 underwent NRA and 621 underwent conventional DST. NRA yielded test results for 78.4% of cases vs. 68.8% for conventional DST (P < 0.0001); the median time to result was 44 vs. 133 days, respectively (adjusted HR 0.64, 95%CI 0.56-0.73). Among individuals without previous anti-tuberculosis treatment, NRA was associated with a favorable treatment outcome (adjusted OR 1.39, 95%CI 1.01-1.90) and prolonged survival (adjusted HR 0.53, 95%CI 0.31-0.90).

CONCLUSION

Direct NRA significantly shortened time to test result and improved treatment outcomes and survival in certain groups.

Rapid detection of rpoB gene mutations conferring rifampin resistance in Mycobacterium tuberculosis

Multidrug-resistant Mycobacterium tuberculosis strains are widespread and present a challenge to effective treatment of this infection. The need for a low-cost and rapid detection method for clinically relevant mutations in Mycobacterium tuberculosis that confer multidrug resistance is urgent, particularly for developing countries. We report here a novel test that detects the majority of clinically relevant mutations in the beta subunit of the RNA polymerase (rpoB) gene that confer resistance to rifampin (RIF), the treatment of choice for tuberculosis (TB). The test, termed TB ID/R, combines a novel target and temperature-dependent RNase H2-mediated cleavage of blocked DNA primers to initiate isothermal helicase-dependent amplification of a rpoB gene target sequence. Amplified products are detected by probes arrayed on a modified silicon chip that permits visible detection of both RIF-sensitive and RIF-resistant strains of M. tuberculosis. DNA templates of clinically relevant single-nucleotide mutations in the rpoB gene were created to validate the performance of the TB ID/R test. Except for one rare mutation, all mutations were unambiguously detected. Additionally, 11 RIF-sensitive and 25 RIF-resistant clinical isolates were tested by the TB ID/R test, and 35/36 samples were classified correctly (96.2%). This test is being configured in a low-cost test platform to provide rapid diagnosis and drug susceptibility information for TB in the point-of-care setting in the developing world, where the need is acute.

Patterns of antituberculous drug resistance in Eastern Saudi Arabia: a 7-year surveillance study from 1/2003 to 6/2010

OBJECTIVE

To examine the patterns of antituberculous drug resistance of Mycobacterium tuberculosis in patients with pulmonary and extra-pulmonary tuberculosis in the Eastern province of the Kingdom of Saudi Arabia.

METHODS

This is a retrospective study of antibiotic susceptibility of 1681 non-repetitive M. tuberculosis isolates from 1/2003 to 6/2010.

RESULTS

Of the total patients, 41% (n=687) were Saudis and 59% (n=994) were non-Saudis. The pulmonary and extra-pulmonary specimens constituted 68% (n=1148) and 32% (n=533), respectively. The incidence of resistance was 15.5% to one or more of anti-tuberculosis drugs. The resistance rates to first-line drugs were as follows: streptomycin (10.4%), INH (9.8%), rifampicin (1.5%) and ethambutol (1.0%). Multi-drug resistant tuberculosis was present in 1.4% (n=24) of the sample.

CONCLUSION

INH resistance in this study was relatively high, whereas the rate of MDR-TB was low. A rate of MDR-TB observed in this study was 1.4%. Thus, an empiric four-drug therapy is required to treat patients with tuberculosis in this area of Saudi Arabia.

Targeted drug-resistance testing strategy for multidrug-resistant tuberculosis detection, Lima, Peru, 2005-2008

Running head: Targeted Drug-Resistance Testing Strategy for MDR TB

The Peruvian National Tuberculosis Control Program issued guidelines in 2006 specifying criteria for culture and drug-susceptibility testing (DST), including district-level rapid DST. All patients referred for culture and DST in 2 districts of Lima, Peru, during January 2005–November 2008 were monitored prospectively. Of 1,846 patients, 1,241 (67.2%) had complete DST results for isoniazid and rifampin; 419 (33.8%) patients had multidrug-resistant (MDR) TB at the time of referral. Among patients with new smear-positive TB, household contact and suspected category I failure were associated with MDR TB, compared with concurrent regional surveillance data. Among previously treated patients with smear-positive TB, adult household contact, suspected category II failure, early relapse after category I, and multiple previous TB treatments were associated with MDR TB, compared with concurrent regional surveillance data. The proportion of MDR TB detected by using guidelines was higher than that detected by a concurrent national drug-resistance survey, indicating that the strategy effectively identified patients for DST.

Structure activity relationship, acute toxicity and cytotoxicity of antimycobacterial neolignan analogues

OBJECTIVES

The study's aims were to evaluate the antimycobacterial activity of 13 synthetic neolignan analogues and to perform structure activity relationship analysis (SAR). The cytotoxicity of the compound 2-phenoxy-1-phenylethanone (LS-2, 1) in mammalian cells, such as the acute toxicity in mice, was also evaluated.

METHODS

The extra and intracellular antimycobacterial activity was evaluated on Mycobacterium tuberculosis H37Rv. Cytotoxicity studies were performed using V79 cells, J774 macrophages and rat hepatocytes. Additionally, the in-vivo acute toxicity was tested in mice. The SAR analysis was performed by Principal Component Analysis (PCA).

KEY FINDINGS

Among the 13 analogues tested, LS-2 (1) was the most effective, showing promising antimycobacterial activity and very low cytotoxicity in V79 cells and in J774 macrophages, while no toxicity was observed in rat hepatocytes. The selectivity index (SI) of LS-2 (1) was 91 and the calculated LD50 was 1870 mg/kg, highlighting the very low toxicity in mice. SAR analysis showed that the highest electrophilicity and the lowest molar volume are physical-chemical characteristics important for the antimycobacterial activity of the LS-2 (1).

CONCLUSIONS

LS-2 (1) showed promising antimycobacterial activity and very weak cytotoxicity in cell culture, as well as an absence of toxicity in primary culture of hepatocytes. In the acute toxicity study there was an indication of absence of toxicity on murine models, in vivo.

Induction of β-defensins by l-isoleucine as novel immunotherapy in experimental murine tuberculosis

Tuberculosis is a worldwide health problem, and multidrug-resistant (MDR) and extensively multidrug-resistant (XMDR) strains are rapidly emerging and threatening the control of this disease. These problems motivate the search for new treatment strategies. One potential strategy is immunotherapy using cationic anti-microbial peptides. The capacity of l-isoleucine to induce beta-defensin expression and its potential therapeutic efficiency were studied in a mouse model of progressive pulmonary tuberculosis. BALB/c mice were infected with Mycobacterium tuberculosis strain H37Rv or with a MDR clinical isolate by the intratracheal route. After 60 days of infection, when disease was in its progressive phase, mice were treated with 250 µg of intratracheal l-isoleucine every 48 h. Bacillary loads were determined by colony-forming units, protein and cytokine gene expression were determined by immunohistochemistry and reverse transcription-quantitative polymerase chain reaction (RT-qPCR), respectively, and tissue damage was quantified by automated morphometry. Administration of l-isoleucine induced a significant increase of beta-defensins 3 and 4 which was associated with decreased bacillary loads and tissue damage. This was seen in animals infected with the antibiotic-sensitive strain H37Rv and with the MDR clinical isolate. Thus, induction of beta-defensins might be a potential therapy that can aid in the control of this significant infectious disease.

Heightened vulnerability to MDR-TB epidemics after controlling drug-susceptible TB

BACKGROUND

Prior infection with one strain TB has been linked with diminished likelihood of re-infection by a new strain. This paper attempts to determine the role of declining prevalence of drug-susceptible TB in enabling future epidemics of MDR-TB.

METHODS

A computer simulation of MDR-TB epidemics was developed using an agent-based model platform programmed in NetLogo (See http://mdr.tbtools.org/). Eighty-one scenarios were created, varying levels of treatment quality, diagnostic accuracy, microbial fitness cost, and the degree of immunogenicity elicited by drug-susceptible TB. Outcome measures were the number of independent MDR-TB cases per trial and the proportion of trials resulting in MDR-TB epidemics for a 500 year period after drug therapy for TB is introduced.

RESULTS

MDR-TB epidemics propagated more extensively after TB prevalence had fallen. At a case detection rate of 75%, improving therapeutic compliance from 50% to 75% can reduce the probability of an epidemic from 45% to 15%. Paradoxically, improving the case-detection rate from 50% to 75% when compliance with DOT is constant at 75% increases the probability of MDR-TB epidemics from 3% to 45%.

CONCLUSIONS

The ability of MDR-TB to spread depends on the prevalence of drug-susceptible TB. Immunologic protection conferred by exposure to drug-susceptible TB can be a crucial factor that prevents MDR-TB epidemics when TB treatment is poor. Any single population that successfully reduces its burden of drug-susceptible TB will have reduced herd immunity to externally or internally introduced strains of MDR-TB and can experience heightened vulnerability to an epidemic. Since countries with good TB control may be more vulnerable, their self interest dictates greater promotion of case detection and DOTS implementation in countries with poor control to control their risk of MDR-TB.

New old challenges in tuberculosis: potentially effective nanotechnologies in drug delivery

Tuberculosis (TB) is the second most deadly infectious disease. Despite potentially curative pharmacotherapies being available for over 50 years, the length of the treatment and the pill burden can hamper patient lifestyle. Thus, low compliance and adherence to administration schedules remain the main reasons for therapeutic failure and contribute to the development of multi-drug-resistant (MDR) strains. Pediatric patients constitute a high risk population. Most of the first-line drugs are not commercially available in pediatric form. The design of novel antibiotics attempts to overcome drug resistance, to shorten the treatment course and to reduce drug interactions with antiretroviral therapies. On the other hand, the existing anti-TB drugs are still effective. Overcoming technological drawbacks of these therapeutic agents as well as improving the effectiveness of the drug by targeting the infection reservoirs remains the central aims of Pharmaceutical Technology. In this framework, nanotechnologies appear as one of the most promising approaches for the development of more effective and compliant medicines. The present review thoroughly overviews the state-of-the-art in the development of nano-based drug delivery systems for encapsulation and release of anti-TB drugs and discusses the challenges that are faced in the development of a more effective, compliant and also affordable TB pharmacotherapy.

Tuberculous pleural effusion

Tuberculous pleural effusion is one of the most common forms of extrapulmonary tuberculosis (TB). The immediate cause of the effusion is a delayed hypersensitivity response to mycobacterial antigens in the pleural space. For this reason microbiological analyses are often negative and limited by the lengthy delay in obtaining results. In areas with high TB prevalence, pleural fluid adenosine deaminase (ADA) levels greater than 40 U/l argue strongly for TB; in contrast, low levels of pleural ADA have high negative predictive value in low-prevalence countries. The specificity of this enzyme increases if only lymphocytic exudates are considered. The shortcoming of the ADA test is its inability to provide culture and drug sensitivity information, which is paramount in countries with a high degree of resistance to anti-TB drugs. Sputum induction (in addition to pleural fluid) for acid-fast bacilli and culture is a recommended procedure in all patients with TB pleurisy. The microscopic-observation drug-susceptibility assay performed on pleural fluid or pleural tissue increases by two to three times the detection of TB over conventional cultures, and it allows for the identification of multidrug-resistant TB. A reasonable management strategy for pleural TB would be to initiate a four-drug regimen and perform a therapeutic thoracentesis in patients with large, symptomatic effusions.

Recent advances in the diagnosis and treatment of multidrug-resistant tuberculosis

Tuberculosis (TB) is a major infectious disease killing nearly two million people, mostly in developing countries, every year. The increasing incidence of resistance of Mycobacterium tuberculosis strains to the most-effective (first-line) anti-TB drugs is a major factor contributing to the current TB epidemic. Drug-resistant strains have evolved mainly due to incomplete or improper treatment of TB patients. Resistance of M. tuberculosis to anti-TB drugs is caused by chromosomal mutations in genes encoding drug targets. Multidrug-resistant (resistant at least to rifampin and isoniazid) strains of M. tuberculosis (MDR-TB) evolve due to sequential accumulation of mutations in target genes. Emergence and spreading of MDR-TB strains is hampering efforts for the control and management of TB. The MDR-TB is also threatening World Health Organization's target of tuberculosis elimination by 2050. Proper management of MDR-TB relies on early recognition of such patients. Several diagnostic methods, both phenotypic and molecular, have been developed recently for rapid identification of MDR-TB strains from suspected patients and some are also suitable for resource-poor countries. Once identified, successful treatment of MDR-TB requires therapy with several effective drugs some of which are highly toxic, less efficacious and expensive. Minimum treatment duration of 18-24 months is also long, making it difficult for health care providers to ensure adherence to treatment. Successful treatment has been achieved by supervised therapy with appropriate drugs at institutions equipped with facilities for culture, drug susceptibility testing of MDR-TB strains to second-line drugs and regular monitoring of patients for adverse drug reactions and bacteriological and clinical improvement.

Doomsday postponed? Preventing and reversing epidemics of drug-resistant tuberculosis

Extensively drug-resistant (XDR) strains of Mycobacterium tuberculosis, now known to be present in 50 countries, heighten the threat posed by untreatable and fatal human tuberculosis (TB). To combat epidemics of drug-resistant TB, it is vital to understand why some resistant strains have greater reproductive fitness--a greater propensity to spread--than drug-susceptible strains. If public health malpractice has been a more important determinant of reproductive success than genetic mechanisms, then improved diagnosis and treatment could keep the frequency of resistant strains among TB cases low in any population. Recent data suggest that national TB control programmes that use existing drugs efficiently can postpone and even reverse epidemics of multidrug-resistant TB, although the effect of such programmes on XDR strains remains largely unknown.