Designing and Evaluating Interventions to Halt the Transmission of Tuberculosis

Backtranslation of human RNA biosignatures of tuberculosis disease risk into the preclinical pipeline is condition dependent

It is unclear whether human progression to active tuberculosis disease (TB) risk signatures are viable endpoint criteria for evaluations of treatments in development. TB is the deadliest infectious disease globally and more efficacious vaccines are needed to reduce this mortality. However, the immune correlates of protection for either preventing infection with Mycobacterium tuberculosis or preventing TB disease have yet to be completely defined, making the advancement of candidate vaccines through the pipeline slow, costly, and fraught with risk. Human-derived correlate of risk (COR) gene signatures, which identify an individual's risk of progressing to active TB disease, provide an opportunity for evaluating new therapies for TB with clear and defined endpoints. Though prospective clinical trials with longitudinal sampling are prohibitively expensive, the characterization of COR gene signatures is practical with preclinical models. Using a 3Rs (replacement, reduction, and refinement) approach we reanalyzed heterogeneous publicly available transcriptional data sets to determine whether a specific set of COR signatures are viable endpoints in the preclinical pipeline. We selected RISK6, Sweeney3, and BATF2 human-derived blood-based RNA biosignatures because they require relatively few genes and have been carefully evaluated across several clinical cohorts. These data suggest that in certain experimental designs and in several tissue types, human COR signatures correlate with disease progression as measured by the bacterial burden in the preclinical TB model pipeline. We observed the best performance when the model most closely reflected human infection or disease conditions. Human-derived COR signatures offer an opportunity for high-throughput preclinical endpoint criteria of vaccine and drug therapy evaluations.

IMPORTANCE

Understanding the strengths or limitations of back-translating human-derived correlate of risk (COR) RNA signatures into the preclinical pipeline may help streamline down-selection of therapeutic vaccine and drug candidates and better align preclinical models with proposed clinical trial efficacy endpoints.

Incipient and subclinical tuberculosis: a narrative review

Mycobacterium tuberculosis has been known to infect humans for eons. It is an airborne infectious disease transmitted through droplet nuclei of 1 to 5 µm in diameter. Historically, tuberculosis (TB) was considered a distinct condition characterized by TB infection and active TB disease. However, recently, the concept of a dynamic spectrum of infection has emerged, wherein the pathogen is initially eradicated by the innate or adaptive immune system, either in conjunction with or independently of T cell priming. Other categories within this spectrum include TB infection, incipient TB, subclinical TB, and active TB disease. Various host- and pathogen-related factors influence these categories. Furthermore, subclinical TB can facilitate the spread of infection within the community. Due to its asymptomatic nature, there is a risk of delayed diagnosis, and some patients may remain undiagnosed. Individuals with subclinical TB may stay in this stage for an indeterminate period without progressing to active TB disease, and some may even experience regression. Early diagnosis and treatment of TB are essential to meet the 2035 targets outlined in the end-TB strategy. This strategy should also include incipient and subclinical TB. This review will focus on the definition, natural history, burden, trajectory, transmissibility, detection, and management of early-stage TB.

Backtranslation of human RNA biosignatures of tuberculosis disease risk into the preclinical pipeline is condition dependent

It is not clear whether human progression to active tuberculosis disease (TB) risk signatures are viable endpoint criteria for evaluations of treatments in clinical or preclinical development. TB is the deadliest infectious disease globally and more efficacious vaccines are needed to reduce this mortality. However, the immune correlates of protection for either preventing infection with Mycobacterium tuberculosis or preventing TB disease have yet to be completely defined, making the advancement of candidate vaccines through the pipeline slow, costly, and fraught with risk. Human-derived correlate of risk (COR) gene signatures, which identify an individual's risk to progressing to active TB disease, provide an opportunity for evaluating new therapies for TB with clear and defined endpoints. Though prospective clinical trials with longitudinal sampling are prohibitively expensive, characterization of COR gene signatures is practical with preclinical models. Using a 3Rs (Replacement, Reduction and Refinement) approach we reanalyzed heterogeneous publicly available transcriptional datasets to determine whether a specific set of COR signatures are viable endpoints in the preclinical pipeline. We selected RISK6, Sweeney3 and BATF2 human-derived blood-based RNA biosignatures because they require relatively few genes to assign a score and have been carefully evaluated across several clinical cohorts. Excitingly, these data provide proof-of-concept that human COR signatures seem to have high fidelity across several tissue types in the preclinical TB model pipeline and show best performance when the model most closely reflected human infection or disease conditions. Human-derived COR signatures offer an opportunity for high-throughput preclinical endpoint criteria of vaccine and drug therapy evaluations.

One Sentence Summary

Human-derived biosignatures of tuberculosis disease progression were evaluated for their predictive fidelity across preclinical species and derived tissues using available public data sets.

M. tuberculosis Infection Attributable to Exposure in Social Networks of Tuberculosis Cases in an Urban African Community

Background

The persistence of tuberculosis today and its global disparity send a powerful message that effective tuberculosis control must respond to its regional epidemiology. Active case finding through contact investigation is a standard protocol used for tuberculosis control, but its effectiveness has not been established, especially in endemic areas.

Methods

To quantify the potential effectiveness of contact investigation in Kampala, Uganda, we used a cross-sectional design to evaluate the social networks of 123 tuberculosis index cases and 124 controls without tuberculosis.

Results

Tuberculous infection was present in 515 of 989 tuberculosis case contacts (52.1%) and 396 of 1026 control contacts (38.6%; adjusted prevalence ratio, 1.4; 95% CI, 1.3-1.6). The proportion of infected participants with known exposure within the social network of the tuberculosis case was 35%. The population-attributable fraction was 11.1% for any known exposure, with 7.3% attributable to household exposure and 3.4% attributable to extrahousehold exposure.

Conclusions

This low population-attributable fraction indicates that contact tracing in the social networks of index cases will have only a modest effect in reducing tuberculous infection in a community. New approaches to community-level active case finding are needed.

Connecting the dots: understanding how human mobility shapes TB epidemics

Tuberculosis (TB) remains a leading infectious cause of death worldwide. Reducing TB infections and TB-related deaths rests ultimately on stopping forward transmission from infectious to susceptible individuals. Critical to this effort is understanding how human host mobility shapes the transmission and dispersal of new or existing strains of Mycobacterium tuberculosis (Mtb). Important questions remain unanswered. What kinds of mobility, over what temporal and spatial scales, facilitate TB transmission? How do human mobility patterns influence the dispersal of novel Mtb strains, including emergent drug-resistant strains? This review summarizes the current state of knowledge on mobility and TB epidemic dynamics, using examples from three topic areas, including inference of genetic and spatial clustering of infections, delineating source-sink dynamics, and mapping the dispersal of novel TB strains, to examine scientific questions and methodological issues within this topic. We also review new data sources for measuring human mobility, including mobile phone-associated movement data, and discuss important limitations on their use in TB epidemiology.

Drug resistant tuberculosis: Implications for transmission, diagnosis, and disease management

Drug resistant tuberculosis contributes significantly to the global burden of antimicrobial resistance, often consuming a large proportion of the healthcare budget and associated resources in many endemic countries. The rapid emergence of resistance to newer tuberculosis therapies signals the need to ensure appropriate antibiotic stewardship, together with a concerted drive to develop new regimens that are active against currently circulating drug resistant strains. Herein, we highlight that the current burden of drug resistant tuberculosis is driven by a combination of ongoing transmission and the intra-patient evolution of resistance through several mechanisms. Global control of tuberculosis will require interventions that effectively address these and related aspects. Interrupting tuberculosis transmission is dependent on the availability of novel rapid diagnostics which provide accurate results, as near-patient as is possible, together with appropriate linkage to care. Contact tracing, longitudinal follow-up for symptoms and active mapping of social contacts are essential elements to curb further community-wide spread of drug resistant strains. Appropriate prophylaxis for contacts of drug resistant index cases is imperative to limit disease progression and subsequent transmission. Preventing the evolution of drug resistant strains will require the development of shorter regimens that rapidly eliminate all populations of mycobacteria, whilst concurrently limiting bacterial metabolic processes that drive drug tolerance, mutagenesis and the ultimate emergence of resistance. Drug discovery programs that specifically target bacterial genetic determinants associated with these processes will be paramount to tuberculosis eradication. In addition, the development of appropriate clinical endpoints that quantify drug tolerant organisms in sputum, such as differentially culturable/detectable tubercle bacteria is necessary to accurately assess the potential of new therapies to effectively shorten treatment duration. When combined, this holistic approach to addressing the critical problems associated with drug resistance will support delivery of quality care to patients suffering from tuberculosis and bolster efforts to eradicate this disease.

Prevalence trends of latent tuberculosis infection at the global, regional, and country levels from 1990-2019

OBJECTIVES

To track the prevalence trends of latent tuberculosis infection (LTBI) at the global, regional, and national levels.

METHODS

Data on the prevalence of LTBI were extracted from the Global Burden of Disease database. The average annual percent change (AAPC) was estimated by joinpoint regression and was used to evaluate the epidemic of the disease.

RESULTS

Globally, the prevalence rate of LTBI decreased from 30.66% in 1990 to 23.67% in 2019, with an AAPC of -0.9%. The prevalence rate of LTBI varied from 5.02% (Jordan) to 48.35% (Uganda) in 1990 and from 2.51% (Jordan) to 43.75% (Vietnam) in 2019 at the country level. The prevalence decreased in all the six World Health Organization (WHO) regions and in most countries, with the AAPC ranging from -0.5% in the Western Pacific Region to -2.1% in the European Region and from -4.3% (Bhutan) to -0.1% (Malaysia, Myanmar, South Africa, Tokelau, and Vietnam), respectively. Disparities were also observed among different sex and age groups.

CONCLUSION

The prevalence of LTBI decreased slightly worldwide in the last three decades, but the decrease is slow and not sufficient to meet the targets of WHO tuberculosis elimination. Much more effort and progress should be made in order to decrease the prevalence of LTBI.

Alarming Tuberculosis Rate Among People Who Inject Drugs in Vietnam

BACKGROUND

The tuberculosis (TB) epidemic is not homogeneous in the general population but presents high-risk groups. People who inject drugs (PWID) are such a group. However, TB among PWID remains largely undocumented. Our goal was to assess the prevalence of TB and the risk factors associated with TB among PWID in Vietnam.

METHODS

We implemented a cross-sectional survey among 2 community-based cohorts of human immunodeficiency virus (HIV)-positive and HIV-negative PWID in Hai Phong. Participants were screened for TB using questions on TB symptoms. Those who reported any symptom were accompanied by peers to the TB clinic for chest x-ray. If the latter was abnormal, a sputum was collected to perform an Xpert MTB/RIF test.

RESULTS

A total of 885 PWID were screened for TB. For both cohorts, most PWID were male (>90.0%), with a median age of 42 years. Beside heroin injection, 52.5% of participants reported smoking methamphetamine, and 63.2% were on methadone. Among HIV-positive PWID (N = 451), 90.4% were on antiretroviral therapy and 81.6% had a viral load <1000 copies/mL. Using a complete-case analysis, the estimated TB prevalence was 2.3% (95% confidence interval [CI], 1.0-4.5) and 2.1% (95% CI, 0.8-4.2) among HIV-positive and HIV-negative people, respectively. Living as a couple, arrest over the past 6 months, homelessness, and smoking methamphetamine were independently associated with TB but not HIV infection.

CONCLUSIONS

In the context of very large antiretroviral therapy coverage, this extremely high rate of TB among PWID requires urgent actions.

Estimating Tuberculosis Transmission Risks in a Primary Care Clinic in South Africa: Modeling of Environmental and Clinical Data

BACKGROUND

Congregate settings, such as healthcare clinics, may play an essential role in Mycobacterium tuberculosis (Mtb) transmission. Using patient and environmental data, we studied transmission at a primary care clinic in South Africa.

METHODS

We collected patient movements, cough frequency, and clinical data, and measured indoor carbon dioxide (CO2) levels, relative humidity, and Mtb genomes in the air. We used negative binomial regression model to investigate associations.

RESULTS

We analyzed 978 unique patients who contributed 14 795 data points. The median patient age was 33 (interquartile range [IQR], 26-41) years, and 757 (77.4%) were female. Overall, median CO2 levels were 564 (IQR 495-646) parts per million and were highest in the morning. Median number of coughs per day was 466 (IQR, 368-503), and overall median Mtb DNA copies/μL/day was 4.2 (IQR, 1.2-9.5). We found an increased presence of Mtb DNA in the air of 32% (95% credible interval, 7%-63%) per 100 additional young adults (aged 15-29 years) and 1% (0-2%) more Mtb DNA per 10% increase of relative humidity. Estimated cumulative transmission risks for patients attending the clinic monthly for at least 1 hour range between 9% and 29%.

CONCLUSIONS

We identified young adults and relative humidity as potentially important factors for transmission risks in healthcare clinics. Our approach should be used to detect transmission and evaluate infection control interventions.

The impact of active case finding on transmission dynamics of tuberculosis: A modelling study

Background

In the last decade, active case finding (ACF) strategies for tuberculosis (TB) have been implemented in many diverse settings, with some showing large increases in case detection and reporting at the sub-national level. There have also been several studies which seek to provide evidence for the benefits of ACF to individuals and communities in the broader context. However, there remains no quantification of the impact of ACF with regards to reducing the burden of transmission. We sought to address this knowledge gap and quantify the potential impact of active case finding on reducing transmission of TB at the national scale and further, to determine the intensification of intervention efforts required to bring the reproduction number (R₀) below 1 for TB.

Methods

We adopt a dynamic transmission model that incorporates heterogeneity in risk to TB to assess the impact of an ACF programme (IMPACT TB) on reducing TB incidence in Vietnam and Nepal. We fit the models to country-level incidence data using a Bayesian Markov Chain Monte Carlo approach. We assess the impact of ACF using a parameter in our model, which we term the treatment success rate. Using programmatic data, we estimate how much this parameter has increased as a result of IMPACT TB in the implementation districts of Vietnam and Nepal and quantify additional efforts needed to eliminate transmission of TB in these countries by 2035.

Results

Extending the IMPACT TB programme to national coverage would lead to moderate decreases in TB incidence and would not be enough to interrupt transmission by 2035. Decreasing transmission sufficiently to bring the reproduction number (R0) below 1, would require a further intensification of current efforts, even at the sub-national level.

Conclusions

Active case finding programmes are effective in reducing TB in the short term. However, interruption of transmission in high-burden countries, like Vietnam and Nepal, will require comprehensive incremental efforts. Complementary measures to reduce progression from infection to disease, and reactivation of latent infection, are needed to meet the WHO End TB incidence targets.

Evaluation of the treatment efficacy of systemic care combined with thymopentin and 2HRZE/4HR for primary tuberculosis

OBJECTIVE

To investigate the efficacy of systemic care combined with thymopentin and 2HRZE/4HR in the treatment of primary tuberculosis.

METHODS

The clinical data of 93 patients with primary tuberculosis were retrospectively collected and divided into two groups based on the intervention method. Group A (n=46) was treated only with 2HRZE/4HR, and group B (n=47) was treated with the 2HRZE/4HR combined with thymopentin. Meanwhile, both groups received systematic care. The lesion absorption rate, sputum conversion rate (SCR), T lymphocyte subpopulation count, immunoglobulin level, lung function index, changes in sputum supernatant levels of cytokines before and after treatment, and the occurrence of adverse reactions were compared.

RESULTS

Group B exhibited higher complete absorption rate of foci and lower basic absorption rate than group A (P < 0.05). The SCRs of group B after 2, 4 and 6 months of intervention were higher than those of group A (P < 0.05). Compared with group A, group B had lower CD8⁺ level and higher CD4⁺ and CD3⁺ levels (P < 0.05). Group B also had higher levels of IgA, IgG, and IgM than group A after intervention (P < 0.05). Group B had higher levels of FEV1, PEF, and FVC than group A after intervention (P < 0.05). In contrast to group A, group B had lower IL-4 levels and higher TNF-γ levels (P < 0.05). The incidence rate of adverse events in group B was not significantly different from that in group A (P > 0.05).

CONCLUSION

Systemic care combined with 2HRZE/4HR was effective for treatment of primary tuberculosis, which is beneficial for improving the immunity, SCR, and the inflammatory status, with low incidence of adverse events and a high safety level.

Evidence for the Use of Triage, Respiratory Isolation, and Effective Treatment to Reduce the Transmission of Mycobacterium Tuberculosis in Healthcare Settings: A Systematic Review

Evidence is limited for infection prevention and control (IPC) measures reducing Mycobacterium tuberculosis (MTB) transmission in health facilities. This systematic review, 1 of 7 commissioned by the World Health Organization to inform the 2019 update of global tuberculosis (TB) IPC guidelines, asked: do triage and/or isolation and/or effective treatment of TB disease reduce MTB transmission in healthcare settings? Of 25 included articles, 19 reported latent TB infection (LTBI) incidence in healthcare workers (HCWs; absolute risk reductions 1%-21%); 5 reported TB disease incidence in HCWs (no/slight [high TB burden] or moderate [low burden] reduction) and 2 in human immunodeficiency virus-positive in-patients (6%-29% reduction). In total, 23/25 studies implemented multiple IPC measures; effects of individual measures could not be disaggregated. Packages of IPC measures appeared to reduce MTB transmission, but evidence for effectiveness of triage, isolation, or effective treatment, alone or in combination, was indirect and low quality. Harmonizing study designs and reporting frameworks will permit formal data syntheses and facilitate policy making.

Blood RNA signatures predict recent tuberculosis exposure in mice, macaques and humans

Tuberculosis (TB) is the leading cause of death due to a single infectious disease. Knowing when a person was infected with Mycobacterium tuberculosis (M.tb) is critical as recent infection is the strongest clinical risk factor for progression to TB disease in immunocompetent individuals. However, time since M.tb infection is challenging to determine in routine clinical practice. To define a biomarker for recent TB exposure, we determined whether gene expression patterns in blood RNA correlated with time since M.tb infection or exposure. First, we found RNA signatures that accurately discriminated early and late time periods after experimental infection in mice and cynomolgus macaques. Next, we found a 6-gene blood RNA signature that identified recently exposed individuals in two independent human cohorts, including adult household contacts of TB cases and adolescents who recently acquired M.tb infection. Our work supports the need for future longitudinal studies of recent TB contacts to determine whether biomarkers of recent infection can provide prognostic information of TB disease risk in individuals and help map recent transmission in communities.

Distinct Risk Factors for Clinical and Bacteriologically Confirmed Tuberculosis among Child Household Contacts in a High-Burden Setting

The identification and screening of children at high risk of tuberculosis is essential to the control and prevention of child tuberculosis (TB). BUTIMBA, an active case finding and household contact-tracing project implemented between 2013 and 2015 in Eswatini, evaluated 5,413 contacts of 1,568 index cases, of whom 82 (1.5%) were diagnosed with TB disease. We conducted univariate and multivariate clustered logistic regression analyses of risk factors for any TB diagnosis among child household contacts of TB cases. Children younger than 5 years and children with positive HIV status were more likely to have TB than children aged 5-14 years and children with negative HIV status, respectively (adjusted odds ratio [aOR]: 2.2, P < 0.001; aOR: 5.0, P < 0.001). Children with one or more TB symptoms were more likely to be diagnosed with TB based on clinical criteria, but less likely to have bacteriologically confirmed TB, highlighting subjectivity in determination of child TB.

Modeling Missing Cases and Transmission Links in Networks of Extensively Drug-Resistant Tuberculosis in KwaZulu-Natal, South Africa

Patterns of transmission of drug-resistant tuberculosis (TB) remain poorly understood, despite over half a million incident cases worldwide in 2017. Modeling TB transmission networks can provide insight into drivers of transmission, but incomplete sampling of TB cases can pose challenges for inference from individual epidemiologic and molecular data. We assessed the effect of missing cases on a transmission network inferred from Mycobacterium tuberculosis sequencing data on extensively drug-resistant TB cases in KwaZulu-Natal, South Africa, diagnosed in 2011-2014. We tested scenarios in which cases were missing at random, missing differentially by clinical characteristics, or missing differentially by transmission (i.e., cases with many links were under- or oversampled). Under the assumption that cases were missing randomly, the mean number of transmissions per case in the complete network needed to be larger than 20, far higher than expected, to reproduce the observed network. Instead, the most likely scenario involved undersampling of high-transmitting cases, and models provided evidence for super-spreading. To our knowledge, this is the first analysis to have assessed support for different mechanisms of missingness in a TB transmission study, but our results are subject to the distributional assumptions of the network models we used. Transmission studies should consider the potential biases introduced by incomplete sampling and identify host, pathogen, or environmental factors driving super-spreading.

RISK6, a 6-gene transcriptomic signature of TB disease risk, diagnosis and treatment response

Improved tuberculosis diagnostics and tools for monitoring treatment response are urgently needed. We developed a robust and simple, PCR-based host-blood transcriptomic signature, RISK6, for multiple applications: identifying individuals at risk of incident disease, as a screening test for subclinical or clinical tuberculosis, and for monitoring tuberculosis treatment. RISK6 utility was validated by blind prediction using quantitative real-time (qRT) PCR in seven independent cohorts. Prognostic performance significantly exceeded that of previous signatures discovered in the same cohort. Performance for diagnosing subclinical and clinical disease in HIV-uninfected and HIV-infected persons, assessed by area under the receiver-operating characteristic curve, exceeded 85%. As a screening test for tuberculosis, the sensitivity at 90% specificity met or approached the benchmarks set out in World Health Organization target product profiles for non-sputum-based tests. RISK6 scores correlated with lung immunopathology activity, measured by positron emission tomography, and tracked treatment response, demonstrating utility as treatment response biomarker, while predicting treatment failure prior to treatment initiation. Performance of the test in capillary blood samples collected by finger-prick was noninferior to venous blood collected in PAXgene tubes. These results support incorporation of RISK6 into rapid, capillary blood-based point-of-care PCR devices for prospective assessment in field studies.

A fieldable electrostatic air sampler enabling tuberculosis detection in bioaerosols

Tuberculosis (TB) infects about 25% of the world population and claims more human lives than any other infectious disease. TB is spread by inhalation of aerosols containing viable Mycobacterium tuberculosis expectorated or exhaled by patients with active pulmonary disease. Air-sampling technology could play an important role in TB control by enabling the detection of airborne M. tuberculosis, but tools that are easy to use and scalable in TB hotspots are lacking. We developed an electrostatic air sampler termed the TB Hotspot DetectOR (THOR) and investigated its performance in laboratory aerosol experiments and in a prison hotspot of TB transmission. We show that THOR collects aerosols carrying microspheres, Bacillus globigii spores and M. bovis BCG, concentrating these microparticles onto a collector piece designed for subsequent detection analysis. The unit was also successfully operated in the complex setting of a prison hotspot, enabling detection of a molecular signature for M. tuberculosis in the cough of inmates. Future deployment of this device may lead to a measurable impact on TB case-finding by screening individuals through the aerosols they generate.

Clinical profiles of early and tuberculosis-related mortality in South Korea between 2015 and 2017: a cross-sectional study

BACKGROUND

Although the incidence of tuberculosis (TB) has decreased in South Korea, the mortality rate remains high. TB mortality is a key indicator for TB control interventions. The purpose of this study was to assess early and TB-related mortality during anti-TB treatment and describe the associated clinical characteristics.

METHODS

A multicenter cross-sectional study was performed across South Korea. Patients with pulmonary TB who died during anti-TB treatment and whose records were submitted to the national TB surveillance system between 2015 and 2017 were enrolled. All TB deaths were categorized based on cause (TB-related or non-TB-related) and timing (early or late). We identified statistical associations using the frequency table, chi-square test, and binary logistic regression.

RESULTS

Of 5595 notifiable mortality cases, 3735 patients with pulmonary TB were included in the analysis. There were 2541 (68.0%) male patients, and 2935 (78.6%) mortality cases were observed in patients older than 65 years. There were 944 (25.3%) cases of TB-related death and 2545 (68.1%) cases of early death. Of all cases, 187 (5.0%) patients were diagnosed post-mortem and 38 (1.0%) patients died on the first day of treatment. Low body mass index (adjusted odds ratio (aOR) = 1.26; 95% confidence interval (CI) = 1.08-1.48), no reported illness (aOR = 1.36; 95% CI = 1.10-1.68), bilateral disease on chest X-ray (aOR = 1.30; 95% CI = 1.11-1.52), and positive acid-fast bacilli smear result (aOR = 1.30; 95% CI = 1.11-1.52) were significantly associated with early death, as well as TB-related death. Acute respiratory failure was the most common mode of non-TB-related death. Malignancy was associated with both late (aOR = 0.71; 95% CI = 0.59-0.89) and non-TB-related (aOR = 0.35; 95% CI = 0.26-0.46) death.

CONCLUSIONS

A high proportion of TB death was observed in elderly patients and attributed to non-TB-related causes. Many TB-related deaths occurred during the intensive phase, particularly within the first month. Further studies identifying risk factors for different causes of TB death at different phases of anti-TB treatment are warranted for early targeted intervention in order to reduce TB mortality.

Host Determinants of Infectiousness in Smear-Positive Patients With Pulmonary Tuberculosis

Background

Epidemiologic data suggests that only a minority of tuberculosis (TB) patients are infectious. Cough aerosol sampling is a novel quantitative method to measure TB infectiousness.

Methods

We analyzed data from three studies conducted in Uganda and Brazil over a 13-year period. We included sputum acid fast bacilli (AFB) and culture positive pulmonary TB patients and used a cough aerosol sampling system (CASS) to measure the number of colony-forming units (CFU) of Mycobacterium tuberculosis in cough-generated aerosols as a measure for infectiousness. Aerosol data was categorized as: aerosol negative (CFU = 0) and aerosol positive (CFU > 0). Logistic regression models were built to identify factors associated with aerosol positivity.

Results

M. tuberculosis was isolated by culture from cough aerosols in 100/233 (43%) TB patients. In an unadjusted analysis, aerosol positivity was associated with fewer days of antituberculous therapy before CASS sampling (p = .0001), higher sputum AFB smear grade (p = .01), shorter days to positivity in liquid culture media (p = .02), and larger sputum volume (p = .03). In an adjusted analysis, only fewer days of TB treatment (OR 1.47 per 1 day of therapy, 95% CI 1.16-1.89; p = .001) was associated with aerosol positivity.

Conclusion

Cough generated aerosols containing viable M. tuberculosis, the infectious moiety in TB, are detected in a minority of TB patients and rapidly become non-culturable after initiation of antituberculous treatment. Mechanistic studies are needed to further elucidate these findings.

Assessing tuberculosis control priorities in high-burden settings: a modelling approach

BACKGROUND

In the context of WHO's End TB strategy, there is a need to focus future control efforts on those interventions and innovations that would be most effective in accelerating declines in tuberculosis burden. Using a modelling approach to link the tuberculosis care cascade to transmission, we aimed to identify which improvements in the cascade would yield the greatest effect on incidence and mortality.

METHODS

We engaged with national tuberculosis programmes in three country settings (India, Kenya, and Moldova) as illustrative examples of settings with a large private sector (India), a high HIV burden (Kenya), and a high burden of multidrug resistance (Moldova). We collated WHO country burden estimates, routine surveillance data, and tuberculosis prevalence surveys from 2011 (for India) and 2016 (for Kenya). Linking the tuberculosis care cascade to tuberculosis transmission using a mathematical model with Bayesian melding in each setting, we examined which cascade shortfalls would have the greatest effect on incidence and mortality, and how the cascade could be used to monitor future control efforts.

FINDINGS

Modelling suggests that combined measures to strengthen the care cascade could reduce cumulative tuberculosis incidence by 38% (95% Bayesian credible intervals 27-43) in India, 31% (25-41) in Kenya, and 27% (17-41) in Moldova between 2018 and 2035. For both incidence and mortality, modelling suggests that the most important cascade losses are the proportion of patients visiting the private health-care sector in India, missed diagnosis in health-care settings in Kenya, and drug sensitivity testing in Moldova. In all settings, the most influential delay is the interval before a patient's first presentation for care. In future interventions, the proportion of individuals with tuberculosis who are on high-quality treatment could offer a more robust monitoring tool than routine notifications of tuberculosis.

INTERPRETATION

Linked to transmission, the care cascade can be valuable, not only for improving patient outcomes but also in identifying and monitoring programmatic priorities to reduce tuberculosis incidence and mortality.

FUNDING

US Agency for International Development, Stop TB Partnership, UK Medical Research Council, and Department for International Development.

Transmission of drug-resistant tuberculosis in HIV-endemic settings

The emergence and expansion of the multidrug-resistant tuberculosis epidemic is a threat to the global control of tuberculosis. Multidrug-resistant tuberculosis is the result of the selection of resistance-conferring mutations during inadequate antituberculosis treatment. However, HIV has a profound effect on the natural history of tuberculosis, manifesting in an increased rate of disease progression, leading to increased transmission and amplification of multidrug-resistant tuberculosis. Interventions specific to HIV-endemic areas are urgently needed to block tuberculosis transmission. These interventions should include a combination of rapid molecular diagnostics and improved chemotherapy to shorten the duration of infectiousness, implementation of infection control measures, and active screening of multidrug-resistant tuberculosis contacts, with prophylactic regimens for individuals without evidence of disease. Development and improvement of the efficacy of interventions will require a greater understanding of the factors affecting the transmission of multidrug-resistant tuberculosis in HIV-endemic settings, including population-based molecular epidemiology studies. In this Series article, we review what we know about the transmission of multidrug-resistant tuberculosis in settings with high burdens of HIV and define the research priorities required to develop more effective interventions, to diminish ongoing transmission and the amplification of drug resistance.

The Global Landscape of Tuberculosis Therapeutics

Tuberculosis (TB) is one of the oldest infections afflicting humans yet remains the number one infectious disease killer worldwide. Despite decades of experience treating this disease, TB regimens require months of multidrug therapy, even for latent infections. There have been important recent advances in treatment options across the spectrum of TB, from latent infection to extensively drug-resistant (XDR) TB disease. In addition, new, potent drugs are emerging out of the development pipeline and are being tested in novel regimens in multiple currently enrolling trials. Shorter, safer regimens for many forms of TB are now available or are in our near-term vision. We review recent advances in TB therapeutics and provide an overview of the upcoming clinical trials landscape that will help define the future of worldwide TB treatment.

Where is tuberculosis transmission happening? Insights from the literature, new tools to study transmission and implications for the elimination of tuberculosis

More than 10 million new cases of tuberculosis (TB) are diagnosed worldwide each year. The majority of these cases occur in low- and middle-income countries where the TB epidemic is predominantly driven by transmission. Efforts to 'end TB' will depend upon our ability to halt ongoing transmission. However, recent studies of new approaches to interrupt transmission have demonstrated inconsistent effects on reducing population-level TB incidence. TB transmission occurs across a wide range of settings, that include households and hospitals, but also community-based settings. While home-based contact investigations and infection control programmes in hospitals and clinics have a successful track record as TB control activities, there is a gap in our knowledge of where, and between whom, community-based transmission of TB occurs. Novel tools, including molecular epidemiology, geospatial analyses and ventilation studies, provide hope for improving our understanding of transmission in countries where the burden of TB is greatest. By integrating these diverse and innovative tools, we can enhance our ability to identify transmission events by documenting the opportunity for transmission-through either an epidemiologic or geospatial connection-alongside genomic evidence for transmission, based upon genetically similar TB strains. A greater understanding of locations and patterns of transmission will translate into meaningful improvements in our current TB control activities by informing targeted, evidence-based public health interventions.