The use of mathematical modeling studies for evidence synthesis and guideline development: A glossary.

Mathematical modeling studies are increasingly recognised as an important tool for evidence synthesis and to inform clinical and public health decision-making, particularly when data from systematic reviews of primary studies do not adequately answer a research question. However, systematic reviewers and guideline developers may struggle with using the results of modeling studies, because, at least in part, of the lack of a common understanding of concepts and terminology between evidence synthesis experts and mathematical modellers. The use of a common terminology for modeling studies across different clinical and epidemiological research fields that span infectious and non-communicable diseases will help systematic reviewers and guideline developers with the understanding, characterisation, comparison, and use of mathematical modeling studies. This glossary explains key terms used in mathematical modeling studies that are particularly salient to evidence synthesis and knowledge translation in clinical medicine and public health.

High Prevalence of Active and Latent Tuberculosis in Children and Adolescents in Tibetan Schools in India: The Zero TB Kids Initiative in Tibetan Refugee Children.

BACKGROUND: Tuberculosis (TB) prevalence is high among Tibetan refugees in India, with almost half of cases occurring in congregate facilities, including schools. A comprehensive program of TB case finding and treatment of TB infection (TBI) was undertaken in schools for Tibetan refugee children. METHODS: Schoolchildren and staff in Tibetan schools in Himachal Pradesh, India, were screened for TB with an algorithm using symptoms, chest radiography, molecular diagnostics, and tuberculin skin testing. Individuals with active TB were treated and those with TBI were offered isoniazid-rifampicin preventive therapy for 3 months. RESULTS: From April 2017 to March 2018, we screened 5391 schoolchildren (median age, 13 years) and 786 staff in 11 Tibetan schools. Forty-six TB cases, including 1 with multidrug resistance, were found in schoolchildren, for a prevalence of 853 per 100 000. Extensively drug-resistant TB was diagnosed in 1 staff member. The majority of cases (66%) were subclinical. TBI was detected in 930 of 5234 (18%) schoolchildren and 334 of 634 (53%) staff who completed testing. Children in boarding schools had a higher prevalence of TBI than children in day schools (915/5020 [18%] vs 15/371 [4%]; P < .01). Preventive therapy was provided to 799 of 888 (90%) schoolchildren and 101 of 332 (30%) staff with TBI; 857 (95%) people successfully completed therapy. CONCLUSIONS: TB prevalence is extremely high among Tibetan schoolchildren. Effective active case finding and a high uptake and completion of preventive therapy for children were achieved. With leadership and community mobilization, TB control is implementable on a population level.

Cross-border outbreak of extensively drug-resistant tuberculosis linked to a university in Romania.

Extensively drug-resistant (XDR) tuberculosis (TB) poses a threat to public health due to its complicated, expensive and often unsuccessful treatment. A cluster of three XDR TB cases was detected among foreign medical students of a Romanian university. The contact investigations included tuberculin skin testing or interferon gamma release assay, chest X-ray, sputum smear microscopy, culture, drug susceptibility testing, genotyping and whole-genome sequencing (WGS), and were addressed to students, personnel of the university, family members or other close contacts of the cases. These investigations increased the total number of cases to seven. All confirmed cases shared a very similar WGS profile. Two more cases were epidemiologically linked, but no laboratory confirmation exists. Despite all the efforts done, the source of the outbreak was not identified, but the transmission was controlled. The investigation was conducted by a team including epidemiologists and microbiologists from five countries (Finland, Israel, Romania, Sweden and the UK) and from the European Centre for Disease Prevention and Control. Our report shows how countries can collaborate to control the spread of XDR TB by exchanging information about cases and their contacts to enable identification of additional cases and transmission and to perform the source investigation.

Frequência e perfil epidemiológico de pacientes com tuberculose multirresistente e extensivamente resistente em um hospital de referência na cidade do Rio de Janeiro / Frequency and epidemiological profile of patients with multidrug-resistant and extensively drug-resistant tuberculosis in a reference hospital in the city of Rio de Janeiro

A Tuberculose Multirresistente (TBMR) é um dos grandes problemas de saúde enfrentados em países em desenvolvimento, apresentando-se como um grande desafio global para o controle da Tuberculose (TB). Destacamos ainda o surgimento de formas mais graves de resistência, como a Tuberculose Extensivamente Resistente (TB-XDR). No Brasil foram implantadas diversas estratégias e ações com o objetivo de garantir o controle da doença, sua erradicação e redução nos indices de abandono terapêutico. Porém, na cidade do Rio de Janeiro, o índice de incidência da doença permanece elevado e se destaca como um dos mais altos do Brasil. O presente estudo tem por objetivos, avaliar a frequência e o perfil epidemiológico de pacientes com TBMR e TB-XDR diagnosticados em um Hospital de referência no município do Rio de Janeiro, no período de 2016 a 2018, com a determinação de contribuir para a geração de dados epidemiológicos sobre a situação da doença na cidade do Rio de Janeiro, identificar o grupo de pessoas mais vulneráveis, ajudar a completar o quadro clínico da doença além de estimular outros estudos, sobre o conhecimento da TBMR e TB-XDR. Estudo foi descritivo transversal. Os dados foram secundários coletados através de informações disponíveis em prontuários de pacientes diagnosticados com TB que tiveram como desfecho de interesse a resistência às medicações. Para a obtenção dos dados foi utilizado um instrumento estruturado, que possibilitou a captura de informações referentes à frequencia, o perfil sociodemográfico, características clínico-epidemiológicas, dentre outros. Foi realizada análise das variáveis sociodemógraficas, epidemiológicas e história de tratamento anterior com os resultados coletados armazenados em um banco de dados específico, sendo as análises de frequências e de associações realizadas por meio do software estatístico SPSS. Foram coletados dados de 100 pacientes com TBMR, 44% deles abandonaram o tratamento anteriormente. Dos pacientes investigados 61.6% eram do sexo masculino e 38.4% do sexo feminino. A média de idade encontrada neste estudo foi de 37.9 anos, com a variação entre 18 e 77 anos, 45.3% se declararam pardos e 39.3% possuíam de 4-7 anos de estudo, 19% dos pacientes apresentaram coinfecção HIV/TBMR, foi verificada associação entre abandono de tratamento anterior e caso de TBMR. Podemos concluir que os pacientes que foram encaminhados para tratamento no hospital de estudo apresentaram uma taxa elevada de casos de abandono de tratamento de tuberculose, o que se faz necessário o incremento de ações de planejamento para a adesão ao tratamento da tuberculose.

Multidrug-resistant tuberculosis (MDR-TB) is one of the major health problems faced in developed and developing countries, presenting itself as a major global challenge for Tuberculosis (TB) control. We also highlight the emergence of more severe forms of resistance, such as Extensively Resistant Tuberculosis (TB-XDR). In Brazil several strategies and actions were implemented with the objective of guaranteeing the control of the disease, its eradication and reduction in the rates of therapeutic abandonment. However, in the city of Rio de Janeiro, the incidence rate of the disease remains high and stands out as the highest in Brazil. The present study aims to evaluate the prevalence and epidemiological profile of patients with MDR-TB and MDR-TB diagnosed in a reference hospital in the city of Rio de Janeiro, from 2016 to 2018, with the determination to contribute to the generation epidemiological data on the disease situation in the city of Rio de Janeiro, identifying the group of most vulnerable individuals, helping to complete the clinical picture of the disease, and stimulating other studies on the knowledge of MDR-TB and XDR-TB. The thesis is that patients with MDR-TB and XDR-TB reported in a referral hospital in the city of Rio de Janeiro had abandoned previous treatment. Descriptive cross-sectional study. The data were collected through information available in medical records of patients diagnosed with TB who had as an outcome of interest the resistance to medications. To obtain the data, a structured instrument was used, which enabled the capture of information regarding prevalence, sociodemographic profile, clinical and epidemiological characteristics, among others. An analysis of sociodemographic, epidemiological and previous treatment history was performed with the collected data stored in a specific database, and the frequency and association analyzes were performed using the SPSS statistical software. Data were collected from 100 patients with MDR-TB, 44% of whom had previously discontinued treatment. Of the patients investigated, 61.6% were male and 38.4% female. The mean age found in this study was 37.9 years, ranging from 18 to 77 years, 45.3% were declared pardos and 39.3% had 4-7 years of schooling, 19% of the patients had HIV / MDR coinfection, was verified association between early cessation of treatment and case of MDR-TB. We can conclude that the study hospital had a high rate of cases of abandonment of tuberculosis treatment, which necessitates an increase in planning actions for adherence to tuberculosis treatment.

La Tuberculosis Multirresistente (TBMR) es uno de los grandes problemas de salud enfrentados en los países desarrollados y en desarrollo, presentándose como un gran desafío global para el control de la Tuberculosis (TB). Estamos de acuerdo con el surgimiento de formas más graves de resistencia, la Tuberculosis Extensivamente Resistente (TB-XDR). En Brasil se implantaron diversas estrategias y acciones con el objetivo de garantizar el control de la enfermedad, su erradicación y reducción en las tasas de abandono terapéutico. Sin embargo, en la ciudad de Río de Janeiro, el índice de incidencia de la enfermedad permanece elevado y se destaca como el más alto de Brasil. El presente estudio tiene por objetivos, evaluar la prevalencia y el perfil epidemiológico de pacientes con TBMR y TB-XDR diagnosticados en un Hospital de referencia en el municipio de Río de Janeiro, en el período de 2016 a 2018, con la determinación de contribuir a la generación de datos epidemiológicos sobre la situación de la enfermedad en la ciudad de Río de Janeiro, identificar el grupo de personas más vulnerables, ayudar a completar el cuadro clínico de la enfermedad además de estimular otros estudios, sobre el conocimiento de la TBMR y TB-XDR. la tesis es que los pacientes de TBMR y TB-XDR notificados en un hospital de referencia en la ciudad de Río de Janeiro tuvieron abandono de tratamiento anterior. Estudio descriptivo transversal. Los datos fueron recolectados a través de informaciones disponibles en prontuarios de pacientes diagnosticados con TB que tuvieron como resultado de interés la resistencia a las medicaciones. Para la obtención de los datos se utilizó un instrumento estructurado, que posibilitó la captura de informaciones referentes a la prevalencia, el perfil sociodemográfico, características clínico-epidemiológicas, entre otros. Se realizaron análisis de las variables sociodemóficas, epidemiológicas e historia de tratamiento anterior con los resultados recogidos almacenados en un banco de datos específico, siendo los análisis de frecuencias y de asociaciones realizadas por medio del software estadístico SPSS. Se recogieron datos de 100 pacientes con TBMR, el 44% de ellos abandonaron el tratamiento anteriormente. De los pacientes investigados 61.6% eran del sexo masculino y 38.4% del sexo femenino. La media de edad encontrada en este estudio fue de 37.9 años, con la variación entre 18 y 77 años, el 45.3% se declaró pardos y el 39.3% poseía de 4-7 años de estudio, el 19% de los pacientes presentaron coinfección VIH / TBMR, fue verificada asociación entre el abandono del tratamiento anterior y el caso de TBMR. Podemos concluir que el hospital de estudio presentó una tasa elevada de casos de abandono de tratamiento de tuberculosis, lo que se hace necesario el incremento de acciones de planificación para la adhesión al tratamiento de la tuberculosis.

Extensively Drug-resistant Tuberculosis (XDR-TB): A daunting challenge to the current End TB Strategy and policy recommendations.

Extensively Drug-resistant Tuberculosis (XDR-TB) has emerged as one of the most formidable challenges to the End TB Strategy that has targeted a 95% reduction in TB deaths and 90% reduction in cases by 2035. Globally, there were an estimated 55,100 new XDR-TB cases in 2015 in 117 countries. However, only one in 30 XDR-TB cases had been reported so far. Drug susceptibility test (DST) is the mainstay for diagnosing XDR-TB, but the lack of laboratory facilities in the resource-limited endemic countries limit its uses. A few new drugs including bedaquiline and delamanid, have the potential to improve the efficiency of XDR-TB treatment, but the drugs have been included in 39 countries only. The costs of XDR-TB treatment are several folds higher than that of the MDR-TB. Despite the financing from the donors, there is an urgent need to fill the current funding gap of US$ 2 billion to ensure effective treatment and robust surveillance. In the review article we have addressed current update on XDR-TB, including surveillance, diagnosis and the interventions needed to treat and limit its spread, emphasis on extensive financial support for implementing of current recommendations to meet the goals of End TB Strategy.

Provider perspectives on drug-resistant tuberculosis and human immunodeficiency virus care in South Africa: a qualitative case study.

OBJECTIVE: To examine influences on health care workers' (HCWs') capacity to deliver health care for multi- and/or extensively drug-resistant tuberculosis (MDR/XDR-TB) and human immunodeficiency virus (HIV) infection in South Africa. DESIGN: Qualitative data were collected via group and individual interviews with a purposive sample of 17 HCWs at a centralised, tertiary TB facility and analysed using grounded theory. RESULTS: Four themes were identified: 1) personal infection control practices among HCWs may be weakened by a workplace culture comprising low motivation, disparate risk perceptions and practices across workforce hierarchies, physical discomfort, and problems managing patients with treatment-induced hearing loss. 2) Patient-provider interactions are likely stronger among nurses, and in HIV vs. MDR/XDR-TB service delivery, due to greater attention to patient empowerment and support. Stigma associated with MDR/XDR-TB, considered worse than HIV, may be perpetuated within non-specialised facilities less familiar with MDR/XDR-TB. 3) HCWs who struggle with the daily tedium of MDR/XDR-TB treatment supervision are becoming increasingly supportive of treatment literacy and self-administration. 4) Effective integration of HIV and MDR/XDR-TB services may be impeded by administrative restrictions, workplace norms and provider mindsets. CONCLUSION: Comprehensive, decentralised management of MDR/XDR-TB and HIV coinfection requires the creation of patient-provider trust and treatment literacy in MDR/XDR-TB programmes, and defying workplace norms that could provoke nosocomial TB exposure and fragmented service provision.

XDR-TB transmission in London: Case management and contact tracing investigation assisted by early whole genome sequencing.

OBJECTIVES: We describe the first published cluster of extensively drug resistant Tuberculosis (XDR-TB) in the UK and show how early whole genome sequencing (WGS) of Mtb can assist in case management and contact investigations. METHODS: We describe the contact tracing investigation undertaken after the presentation of an adult with XDR-TB. Active cases were treated with an XDR-TB drug regimen and contacts underwent a programme of follow-up for 2 years. All isolates of Mycobacterium tuberculosis (Mtb) were assessed early using whole genome sequencing (WGS) as well as routine drug susceptibility testing (DST). RESULTS: Thirty-three contacts were screened. In the first year one confirmed and one probable case were identified through contact tracing. A further possible case was identified through epidemiological links. Two confirmed cases were identified through WGS 2 years later. Twenty-five (80%) contacts without evidence of tuberculosis were adherent to 1 year of follow-up and 14 (45%) were adherent to 2 years of follow-up. WGS of Mtb was used to guide drug choices, rapidly identify transmission events, and alter public health management. CONCLUSION: WGS of Mtb enabled rapid effective individualized treatment and facilitated public health interventions by early identification of transmission events.

Multidrug-resistant tuberculosis in Lithuania - Still a long way ahead.

Despite the recent advances in the diagnosis of tuberculosis, treatment of the disease, for the most part, remains the same as it was half a century ago. In recent years only two new anti-tuberculosis drugs have been approved by the European Medicines Agency and Food and Drug Administration. Though the prevalence of this disease is slowly decreasing all over Europe, new challenges appear. One of them is multidrug-resistant tuberculosis (MDR-TB). This problem is especially prominent in Lithuania, which is one of the 27 high MDR-TB burden countries in the world and falls behind neighboring countries in terms of the prevalence of the disease. The objective of this paper was to review the situation of tuberculosis and MDR-TB in Lithuania, and current available methods of treatment, control and diagnosis of this disease.

Drug resistance profiles of new- and previously treated patients with pulmonary tuberculosis in Ibadan, Nigeria.

BACKGROUND: Information on TB drug resistance profiles and its' associated risk factors are scarce in Nigeria despite the large burden of disease in the country. The study was designed to report drug resistance profiles of new- and previously treated patients with pulmonary tuberculosis (TB) in Ibadan, Nigeria. METHOD: Sputum from consenting pulmonary TB patients were collected and cultured for Mycobacterium tuberculosis (Mtb) at the TB laboratory of the University College Hospital, Ibadan, Nigeria using standard method. Mtb were stored and sent for drug susceptibility testing against first and second-line anti-TB drugs at the MRC Unit, The Gambia and at the Institute of Tropical Medicine, Antwerp, Belgium using BACTEC MGIT 960 and proportion method on solid medium respectively. RESULTS: Of 238 Mtb collected, 124 (52.1%) were viable, 102 (59.65%) non-viable while 12 (7.02%) were contaminated. About half (58.87%) of the Mtb were from previously treated patients, 40 (32.26%) were from new patients while treatment history of 1.1 (8.87%) were unknown. Forty-seven (37.90%) of the 124 Mtb. tested were multidrug resistant (MDR) out of which, 40 (85.10%) were from previously treated patients.. HIV prevalence was 8.69%. Of the 17 MDR-TB from previously treated cases tested for second-line drugs, four (23.53%) were resistant to fluoroquinolones or injectable agents, 13 (76.47%) were susceptible while none was resistant to both of these classes of drugs. CONCLUSION: MDR-TB in Ibadan already demonstrates resistance to second line anti-TB drugs hence management of MDR-TB patients should be strengthened to prevent emergence of extensively drug-resistant TB (XDR-TB).

Perspectives on Advances in Tuberculosis Diagnostics, Drugs, and Vaccines.

Despite concerted efforts over the past 2 decades at developing new diagnostics, drugs, and vaccines with expanding pipelines, tuberculosis remains a global emergency. Several novel diagnostic technologies show promise of better point-of-care rapid tests for tuberculosis including nucleic acid-based amplification tests, imaging, and breath analysis of volatile organic compounds. Advances in new and repurposed drugs for use in multidrug-resistant (MDR) or extensively drug-resistant (XDR) tuberculosis have focused on development of several new drug regimens and their evaluation in clinical trials and now influence World Health Organization guidelines. Since the failure of the MVA85A vaccine 2 years ago, there have been no new tuberculosis vaccine candidates entering clinical testing. The current status quo of the lengthy treatment duration and poor treatment outcomes associated with MDR/XDR tuberculosis and with comorbidity of tuberculosis with human immunodeficiency virus and noncommunicable diseases is unacceptable. New innovations and political and funder commitment for early rapid diagnosis, shortening duration of therapy, improving treatment outcomes, and prevention are urgently required.

Consolidated Action Plan to Prevent and Combat Multidrug- and Extensively Drug-resistant Tuberculosis in the WHO European Region 2011-2015: Cost-effectiveness analysis.

Drug-resistant tuberculosis (TB) has increased at an alarming rate in the WHO European Region. Of the 27 countries worldwide with a high burden of multidrug resistant-TB (MDR-TB), 15 are in the European Region. An estimated 78,000 new cases of MDR-TB occur annually in the Region, of which approximately 10% are extensively drug-resistant (XDR)-TB. In response, the WHO Regional Office for Europe developed a Consolidated Action Plan to Prevent and Combat Multidrug- and Extensively Drug-resistant Tuberculosis (2011-2015). Our objective was to analyse the cost-effectiveness of implementing the plan, with the expected achievements of diagnosing 85% of estimated MDR-TB cases and treating at least 75% successfully. A transmission model, using epidemiological data reported to WHO was developed to calculate expected achievements. WHO-CHOICE database was used for cost analyses. The highly cost-effective plan is expected to prevent the emergence of 250,000 new MDR-TB and 13,000 XDR-TB patients respectively, saving US$7 billion and 120,000 lives. The plan and accompanying Resolution were fully endorsed by the sixty-first session of the WHO Regional Committee for Europe in 2011. Member States need to continuously improve health system performance and address TB determinants. Research and development of new medicines, tools and patient-friendly services are also crucial.

Tuberculosis - A global emergency: Tools and methods to monitor, understand, and control the epidemic with specific example of the Beijing lineage.

We argue in favor of a concerted and coordinated response to stop tuberculosis (TB) by monitoring global TB spread, drug-resistance surveillance and populations at risk using available molecular and web tools to identify circulating clones of Mycobacterium tuberculosis complex (MTBC). We took specific example of the Beijing lineage associated with worldwide emergence of both multiple, and extensively drug resistant (MDR/XDR)-TB. The study dataset (n=10,850 isolates, 92 countries of patient origin) was extracted from our multimarker SITVIT2 database on MTBC genotyping (n=111,635 isolates, 169 countries of patient origin). Epidemiological and demographic information in conjunction with spoligotyping (n=10,850), MIRU-VNTR minisatellites (n=2896), and drug resistance (n=2846) data was mapped at macro-geographical (United Nations subregions) and country level, followed by statistical, bioinformatical, and phylogenetical analysis. The global male/female sex ratio was 1.96, the highest being 4.93 in Russia vs. range of 0.8-1.13 observed in Central America, Caribbean, Eastern Africa and Northern Europe (p < 0.0001). The major patient age-group was 21-40 yrs worldwide except Japan (with majority of patients >60 yrs). Younger patients were more common in South America, South Asia, and Western Africa since 25-33% of TB cases due to Beijing genotype occurred in the age group 0-20 yrs. A continuous progression in the proportion of MDR and XDR strains is visible worldwide since 2003 and 2009 respectively. Pansusceptible TB mainly concerned older patients >60 yrs (44%) whereas Drug resistant, MDR and XDR-TB concerned patients preferentially aged 21-40 yrs (between 52 and 58%). Although the proportion of SIT1 pattern vs. other patterns was very high (93%); the proportion of MDR was highest for an emerging genotype SIT190 (p < 0.0001). Lastly, proportion of pansusceptible strains was highest in Japan, while MDR/XDR strains were most common in Russia and Northern Europe. We underline remarkable macro/micro-geographical cleavages in phylogenetic and epidemiologic diversity of Beijing genotype, with phylogeographical specificity of certain genotypes.

Strong decrease in streptomycin-resistance and absence of XDR 12 years after the Reorganization of the National Tuberculosis Control Program in the Central Region of Cameroon.

BACKGROUND: In the 1990s, resistance rates of 15% for streptomycin-resistance and 0.6% for multidrug-resistance (MDR) were reported from the Central Region of Cameroon. This work assesses drug resistant tuberculosis in this region 12 years after reorganization of the National Tuberculosis Control Program (NTCP). METHODS: This cross-sectional study was conducted from April 2010 to March 2011 in Jamot Hospital in Yaoundé, Cameroon. Only patients with smear positive pulmonary tuberculosis were included. Sputa were cultured and subsequently underwent drug susceptibility testing (DST). All consenting individuals were tested for their HIV status. RESULTS: A total of 665 smear positive pulmonary tuberculosis patients were enrolled. The HIV prevalence was 28.5% (95%CI [25.2-32.1]). Of the 582 sputa that grew Mycobacterium tuberculosis complex species, DST results were obtained for 576. The overall resistance rate was 10.9% (63/576). The overall resistance rates for single drug resistance were: isoniazid-resistance 4.7% (27/576), streptomycin-resistance 3.3% (19/576), rifampicin-resistance 0.2% (1/576), kanamycin-resistance 0.2% (1/576) and ofloxacin-resistance 0.2% (1/576). The MDR rate was 1.1% (6/576) and no extensively drug resistant tuberculosis (XDR) was detected. CONCLUSIONS: The data show that reorganization of the NTCP resulted in a strong decrease in streptomycin-resistance and suggest that it prevented the emergence of XDR in the Central Region of Cameroon.

Management of patients with multidrug-resistant/extensively drug-resistant tuberculosis in Europe: a TBNET consensus statement.

The emergence of multidrug-resistant (MDR) and extensively drug-resistant (XDR) tuberculosis (TB) substantially challenges TB control, especially in the European Region of the World Health Organization, where the highest prevalence of MDR/XDR cases is reported. The current management of patients with MDR/XDR-TB is extremely complex for medical, social and public health systems. The treatment with currently available anti-TB therapies to achieve relapse-free cure is long and undermined by a high frequency of adverse drug events, suboptimal treatment adherence, high costs and low treatment success rates. Availability of optimal management for patients with MDR/XDR-TB is limited even in the European Region. In the absence of a preventive vaccine, more effective diagnostic tools and novel therapeutic interventions the control of MDR/XDR-TB will be extremely difficult. Despite recent scientific advances in MDR/XDR-TB care, decisions for the management of patients with MDR/XDR-TB and their contacts often rely on expert opinions, rather than on clinical evidence. This document summarises the current knowledge on the prevention, diagnosis and treatment of adults and children with MDR/XDR-TB and their contacts, and provides expert consensus recommendations on questions where scientific evidence is still lacking.

Risk factors for extensively drug-resistant tuberculosis: a review.

INTRODUCTION: Extensively drug-resistant tuberculosis (XDR-TB) is emerging as a global public health problem. Its treatment is more expensive and difficult, and the outcomes much severe. The identification of risk factors for XDR-TB is of paramount importance to design effective TB control strategies. OBJECTIVE: To review published articles on risk factors for XDR-TB. METHODS: We identified 249 English articles on PubMed, and 182 were excluded by the abstract. The remaining articles were retrieved for full-text detailed evaluation by authors, and 27 relevant articles were selected for final review. RESULTS: Some risk factors were consistently present, mainly previous TB treatment and its length. Other conditions often associated were immigration, alcoholism and HIV coinfection. Pre-XDR-TB points to an increased risk of XDR-TB. CONCLUSION: The information regarding determinants of XDR-TB is relatively weak. However, special emphasis should be given to minimize the risks of TB retreatment to prevent the emergence of highly resistant TB.