Rapid, comprehensive, and affordable mycobacterial diagnosis with whole-genome sequencing: a prospective study

A brief primer on genomic epidemiology: lessons learned from Mycobacterium tuberculosis

Genomics is now firmly established as a technique for the investigation and reconstruction of communicable disease outbreaks, with many genomic epidemiology studies focusing on revealing transmission routes of Mycobacterium tuberculosis. In this primer, we introduce the basic techniques underlying transmission inference from genomic data, using illustrative examples from M. tuberculosis and other pathogens routinely sequenced by public health agencies. We describe the laboratory and epidemiological scenarios under which genomics may or may not be used, provide an introduction to sequencing technologies and bioinformatics approaches to identifying transmission-informative variation and resistance-associated mutations, and discuss how variation must be considered in the light of available clinical and epidemiological information to infer transmission.

The role of whole genome sequencing in antimicrobial susceptibility testing of bacteria: report from the EUCAST Subcommittee

Whole genome sequencing (WGS) offers the potential to predict antimicrobial susceptibility from a single assay. The European Committee on Antimicrobial Susceptibility Testing established a subcommittee to review the current development status of WGS for bacterial antimicrobial susceptibility testing (AST). The published evidence for using WGS as a tool to infer antimicrobial susceptibility accurately is currently either poor or non-existent and the evidence / knowledge base requires significant expansion. The primary comparators for assessing genotypic-phenotypic concordance from WGS data should be changed to epidemiological cut-off values in order to improve differentiation of wild-type from non-wild-type isolates (harbouring an acquired resistance). Clinical breakpoints should be a secondary comparator. This assessment will reveal whether genetic predictions could also be used to guide clinical decision making. Internationally agreed principles and quality control (QC) metrics will facilitate early harmonization of analytical approaches and interpretive criteria for WGS-based predictive AST. Only data sets that pass agreed QC metrics should be used in AST predictions. Minimum performance standards should exist and comparative accuracies across different WGS laboratories and processes should be measured. To facilitate comparisons, a single public database of all known resistance loci should be established, regularly updated and strictly curated using minimum standards for the inclusion of resistance loci. For most bacterial species the major limitations to widespread adoption for WGS-based AST in clinical laboratories remain the current high-cost and limited speed of inferring antimicrobial susceptibility from WGS data as well as the dependency on previous culture because analysis directly on specimens remains challenging. For most bacterial species there is currently insufficient evidence to support the use of WGS-inferred AST to guide clinical decision making. WGS-AST should be a funding priority if it is to become a rival to phenotypic AST. This report will be updated as the available evidence increases.

Genomic Analysis of the Evolution of Fluoroquinolone Resistance in Mycobacterium tuberculosis Prior to Tuberculosis Diagnosis

Fluoroquinolones (FQs) are effective second-line drugs for treating antibiotic-resistant tuberculosis (TB) and are being considered for use as first-line agents. Because FQs are used to treat a range of infections, in a setting of undiagnosed TB, there is potential to select for drug-resistant Mycobacterium tuberculosis mutants during FQ-based treatment of other infections, including pneumonia. Here we present a detailed characterization of ofloxacin-resistant M. tuberculosis samples isolated directly from patients in Taiwan, which demonstrates that selection for FQ resistance can occur within patients who have not received FQs for the treatment of TB. Several of these samples showed no mutations in gyrA or gyrB based on PCR-based molecular assays, but genome-wide next-generation sequencing (NGS) revealed minority populations of gyrA and/or gyrB mutants. In other samples with PCR-detectable gyrA mutations, NGS revealed subpopulations containing alternative resistance-associated genotypes. Isolation of individual clones from these apparently heterogeneous samples confirmed the presence of the minority drug-resistant variants suggested by the NGS data. Further NGS of these purified clones established evolutionary links between FQ-sensitive and -resistant clones derived from the same patient, suggesting de novo emergence of FQ-resistant TB. Importantly, most of these samples were isolated from patients without a history of FQ treatment for TB. Thus, selective pressure applied by FQ monotherapy in the setting of undiagnosed TB infection appears to be able to drive the full or partial emergence of FQ-resistant M. tuberculosis, which has the potential to confound diagnostic tests for antibiotic susceptibility and limit the effectiveness of FQs in TB treatment.

Tuberculosis

Tuberculosis (TB) is an airborne infectious disease caused by organisms of the Mycobacterium tuberculosis complex. Although primarily a pulmonary pathogen, M. tuberculosis can cause disease in almost any part of the body. Infection with M. tuberculosis can evolve from containment in the host, in which the bacteria are isolated within granulomas (latent TB infection), to a contagious state, in which the patient will show symptoms that can include cough, fever, night sweats and weight loss. Only active pulmonary TB is contagious. In many low-income and middle-income countries, TB continues to be a major cause of morbidity and mortality, and drug-resistant TB is a major concern in many settings. Although several new TB diagnostics have been developed, including rapid molecular tests, there is a need for simpler point-of-care tests. Treatment usually requires a prolonged course of multiple antimicrobials, stimulating efforts to develop shorter drug regimens. Although the Bacillus Calmette-Guérin (BCG) vaccine is used worldwide, mainly to prevent life-threatening TB in infants and young children, it has been ineffective in controlling the global TB epidemic. Thus, efforts are underway to develop newer vaccines with improved efficacy. New tools as well as improved programme implementation and financing are necessary to end the global TB epidemic by 2035.

Whole genome sequencing for M/XDR tuberculosis surveillance and for resistance testing

Whole genome sequencing (WGS) can help to relate Mycobacterium tuberculosis genomes to one another to assess genetic relatedness and infer the likelihood of transmission between cases. The same sequence data are now increasingly being used to predict drug resistance and susceptibility. Controlling the spread of tuberculosis and providing patients with the correct treatment are central to the World Health Organization's target to 'End TB' by 2035, for which the global prevalence of drug-resistant tuberculosis remains one of the main obstacles to success. So far, WGS has been applied largely to drug-susceptible strains for the purposes of understanding transmission, leaving a number of analytical considerations before transferring what has been learnt from drug-susceptible disease to drug-resistant tuberculosis. We discuss these potential problems here, alongside some of the challenges to characterizing the Mycobacterium tuberculosis 'resistome'-the optimal knowledge-base required for WGS-based assays to successfully direct individualized treatment regimens through the prediction of drug resistance and susceptibility in the future.

Individualizing management of extensively drug-resistant tuberculosis: diagnostics, treatment, and biomarkers

INTRODUCTION

Success rates for treatment of extensively drug resistant tuberculosis (XDR-TB) are low due to limited treatment options, delayed diagnosis and inadequate health care infrastructure. Areas covered: This review analyses existing programmes of prevention, diagnosis and treatment of XDR-TB. Improved diagnostic procedures and rapid molecular tests help to select appropriate drugs and dosages. Drugs dosages can be further tailored to the specific conditions of the patient based on quantitative susceptibility testing of the M. tuberculosis isolate and use of therapeutic drug monitoring. Pharmacovigilance is important for preserving activity of the novel drugs bedaquiline and delamanid. Furthermore, biomarkers of treatment response must be developed and validated to guide therapeutic decisions. Expert commentary: Given the currently poor treatment outcomes and the association of XDR-TB with HIV in endemic regions, a more patient oriented approach regarding diagnostics, drug selection and tailoring and treatment evaluation will improve treatment outcome. The different areas of expertise should be covered by a multidisciplinary team and may involve the transition of patients from hospitalized to home or community-based treatment.

Whole Genome Sequencing Demonstrates Limited Transmission within Identified Mycobacterium tuberculosis Clusters in New South Wales, Australia

Australia has a low tuberculosis incidence rate with most cases occurring among recent immigrants. Given suboptimal cluster resolution achieved with 24-locus mycobacterium interspersed repetitive unit (MIRU-24) genotyping, the added value of whole genome sequencing was explored. MIRU-24 profiles of all Mycobacterium tuberculosis culture-confirmed tuberculosis cases diagnosed between 2009 and 2013 in New South Wales (NSW), Australia, were examined and clusters identified. The relatedness of cases within the largest MIRU-24 clusters was assessed using whole genome sequencing and phylogenetic analyses. Of 1841 culture-confirmed TB cases, 91.9% (1692/1841) had complete demographic and genotyping data. East-African Indian (474; 28.0%) and Beijing (470; 27.8%) lineage strains predominated. The overall rate of MIRU-24 clustering was 20.1% (340/1692) and was highest among Beijing lineage strains (35.7%; 168/470). One Beijing and three East-African Indian (EAI) clonal complexes were responsible for the majority of observed clusters. Whole genome sequencing of the 4 largest clusters (30 isolates) demonstrated diverse single nucleotide polymorphisms (SNPs) within identified clusters. All sequenced EAI strains and 70% of Beijing lineage strains clustered by MIRU-24 typing demonstrated distinct SNP profiles. The superior resolution provided by whole genome sequencing demonstrated limited M. tuberculosis transmission within NSW, even within identified MIRU-24 clusters. Routine whole genome sequencing could provide valuable public health guidance in low burden settings.

Whole genome sequencing of Mycobacterium tuberculosis for detection of drug resistance: a systematic review

OBJECTIVES

We conducted a systematic review to determine the diagnostic accuracy of whole genome sequencing (WGS) of Mycobacterium tuberculosis for the detection of resistance to first- and second-line anti-tuberculosis (TB) drugs.

METHODS

The study was conducted according to the criteria of the Preferred Reporting Items for Systematic Reviews group. A total of 20 publications were included. The sensitivity, specificity, positive-predictive value and negative-predictive value of WGS using phenotypic drug susceptibility testing methods as a reference standard were determined.

RESULTS

Anti-TB agents tested included all first-line drugs, a variety of reserve drugs, as well as new drugs. Polymorphisms in a total of 53 genes were tested for associations with drug resistance. Pooled sensitivity and specificity values for detection of resistance to selected first-line drugs were 0.98 (95% CI 0.93-0.98) and 0.98 (95% CI 0.98-1.00) for rifampicin and 0.97 (95% CI 0.94-0.99) and 0.93 (95% CI 0.91-0.96) for isoniazid, respectively. Due to high heterogeneity in study designs, lack of data, knowledge of resistance mechanisms and clarity on exclusion of phylogenetic markers, there was a significant variation in analytical performance of WGS for the remaining first-line, reserved drugs and new drugs.

CONCLUSIONS

Whole genome sequencing could be considered a promising alternative to existing phenotypic and molecular drug susceptibility testing methods for rifampicin and isoniazid pending standardization of analytical pipelines. To ensure clinical relevance of WGS for detection of M. tuberculosis complex drug resistance, future studies should include information on clinical outcomes.

Personalized Medicine for Chronic Respiratory Infectious Diseases: Tuberculosis, Nontuberculous Mycobacterial Pulmonary Diseases, and Chronic Pulmonary Aspergillosis

Chronic respiratory infectious diseases are causing high rates of morbidity and mortality worldwide. Tuberculosis, a major cause of chronic pulmonary infection, is currently responsible for approximately 1.5 million deaths per year. Although important advances in the fight against tuberculosis have been made, the progress towards eradication of this disease is being challenged by the dramatic increase in multidrug-resistant bacilli. Nontuberculous mycobacteria causing pulmonary disease and chronic pulmonary aspergillosis are emerging infectious diseases. In contrast to other infectious diseases, chronic respiratory infections share the trait of having highly variable treatment outcomes despite longstanding antimicrobial therapy. Recent scientific progress indicates that medicine is presently at a transition stage from programmatic to personalized management. We explain current state-of-the-art management concepts of chronic pulmonary infectious diseases as well as the underlying methods for therapeutic decisions and their implications for personalized medicine. Furthermore, we describe promising biomarkers and techniques with the potential to serve future individual treatment concepts in this field of difficult-to-treat patients. These include candidate markers to improve individual risk assessment for disease development, the design of tailor-made drug therapy regimens, and individualized biomarker-guided therapy duration to achieve relapse-free cure. In addition, the use of therapeutic drug monitoring to reach optimal drug dosing with the smallest rate of adverse events as well as candidate agents for future host-directed therapies are described. Taken together, personalized medicine will provide opportunities to substantially improve the management and treatment outcome of difficult-to-treat patients with chronic respiratory infections.

Microbial bioinformatics 2020

Microbial bioinformatics in 2020 will remain a vibrant, creative discipline, adding value to the ever‐growing flood of new sequence data, while embracing novel technologies and fresh approaches. Databases and search strategies will struggle to cope and manual curation will not be sustainable during the scale‐up to the million‐microbial‐genome era. Microbial taxonomy will have to adapt to a situation in which most microorganisms are discovered and characterised through the analysis of sequences. Genome sequencing will become a routine approach in clinical and research laboratories, with fresh demands for interpretable user‐friendly outputs. The “internet of things” will penetrate healthcare systems, so that even a piece of hospital plumbing might have its own IP address that can be integrated with pathogen genome sequences. Microbiome mania will continue, but the tide will turn from molecular barcoding towards metagenomics. Crowd‐sourced analyses will collide with cloud computing, but eternal vigilance will be the price of preventing the misinterpretation and overselling of microbial sequence data. Output from hand‐held sequencers will be analysed on mobile devices. Open‐source training materials will address the need for the development of a skilled labour force. As we boldly go into the third decade of the twenty‐first century, microbial sequence space will remain the final frontier!

Molecular Typing of Mycobacterium Tuberculosis Strains: A Fundamental Tool for Tuberculosis Control and Elimination

Tuberculosis (TB) is still an important cause of morbidity and mortality worldwide. An improvement of the strategies for disease control is necessary in both low- and high-incidence TB countries. Clinicians, epidemiologists, laboratory specialists, and public health players should work together in order to achieve a significant reduction in TB transmission and spread of drug-resistant strains. Effective TB surveillance relies on early diagnosis of new cases, appropriate therapy, and accurate detection of outbreaks in the community, in order to implement proper TB control strategies. To achieve this goal, information from classical and molecular epidemiology, together with patient clinical data need to be combined. In this review, we summarize the methodologies currently used in molecular epidemiology, namely molecular typing. We will discuss their efficiency to phylogenetically characterize Mycobacterium tuberculosis isolates, and their ability to provide information that can be useful for disease control. We will also introduce next generation sequencing as the methodology that potentially could provide in a short time both, detection of new outbreaks and identification of resistance patterns. This could envision a potential of next generation sequencing as an important tool for accurate patient management and disease control.

Standard Genotyping Overestimates Transmission of Mycobacterium tuberculosis among Immigrants in a Low-Incidence Country

Immigrants from regions with a high incidence of tuberculosis (TB) are a risk group for TB in low-incidence countries such as Switzerland. In a previous analysis of a nationwide collection of 520 Mycobacterium tuberculosis isolates from 2000 to 2008, we identified 35 clusters comprising 90 patients based on standard genotyping (24-locus mycobacterial interspersed repetitive-unit-variable-number tandem-repeat [MIRU-VNTR] typing and spoligotyping). Here, we used whole-genome sequencing (WGS) to revisit these transmission clusters. Genome-based transmission clusters were defined as isolate pairs separated by ≤12 single nucleotide polymorphisms (SNPs). WGS confirmed 17/35 (49%) MIRU-VNTR typing clusters; the other 18 clusters contained pairs separated by >12 SNPs. Most transmission clusters (3/4) of Swiss-born patients were confirmed by WGS, as opposed to 25% (4/16) of the clusters involving only foreign-born patients. The overall clustering proportion was 17% (90 patients; 95% confidence interval [CI], 14 to 21%) by standard genotyping but only 8% (43 patients; 95% CI, 6 to 11%) by WGS. The clustering proportion was 17% (67/401; 95% CI, 13 to 21%) by standard genotyping and 7% (26/401; 95% CI, 4 to 9%) by WGS among foreign-born patients and 19% (23/119; 95% CI, 13 to 28%) and 14% (17/119; 95% CI, 9 to 22%), respectively, among Swiss-born patients. Using weighted logistic regression, we found weak evidence of an association between birth origin and transmission (adjusted odds ratio of 2.2 and 95% CI of 0.9 to 5.5 comparing Swiss-born patients to others). In conclusion, standard genotyping overestimated recent TB transmission in Switzerland compared to WGS, particularly among immigrants from regions with a high TB incidence, where genetically closely related strains often predominate. We recommend the use of WGS to identify transmission clusters in settings with a low incidence of TB.

Clinical use of whole genome sequencing for Mycobacterium tuberculosis

Drug-resistant tuberculosis (TB) remains a major challenge to global health and to healthcare in the UK. In 2014, a total of 6,520 cases of TB were recorded in England, of which 1.4 % were multidrug-resistant TB (MDR-TB). Extensively drug-resistant TB (XDR-TB) occurs at a much lower rate, but the impact on the patient and hospital is severe. Current diagnostic methods such as drug susceptibility testing and targeted molecular tests are slow to return or examine only a limited number of target regions, respectively. Faster, more comprehensive diagnostics will enable earlier use of the most appropriate drug regimen, thus improving patient outcomes and reducing overall healthcare costs. Whole genome sequencing (WGS) has been shown to provide a rapid and comprehensive view of the genotype of the organism, and thus enable reliable prediction of the drug susceptibility phenotype within a clinically relevant timeframe. In addition, it provides the highest resolution when investigating transmission events in possible outbreak scenarios. However, robust software and database tools need to be developed for the full potential to be realized in this specialized area of medicine.

Tuberculosis and mass gatherings-opportunities for defining burden, transmission risk, and the optimal surveillance, prevention, and control measures at the annual Hajj pilgrimage

Tuberculosis (TB) is now the most common infectious cause of death worldwide. In 2014, an estimated 9.6 million people developed active TB. There were an estimated three million people with active TB including 360000 with multidrug-resistant TB (MDR-TB) who were not diagnosed, and such people continue to fuel TB transmission in the community. Accurate data on the actual burden of TB and the transmission risk associated with mass gatherings are scarce and unreliable due to the small numbers studied and methodological issues. Every year, an estimated 10 million pilgrims from 184 countries travel to the Kingdom of Saudi Arabia (KSA) to perform the Hajj and Umrah pilgrimages. A large majority of pilgrims come from high TB burden and MDR-TB endemic areas and thus many may have undiagnosed active TB, sub-clinical TB, and latent TB infection. The Hajj pilgrimage provides unique opportunities for the KSA and the 184 countries from which pilgrims originate, to conduct high quality priority research studies on TB under the remit of the Global Centre for Mass Gatherings Medicine. Research opportunities are discussed, including those related to the definition of the TB burden, transmission risk, and the optimal surveillance, prevention, and control measures at the annual Hajj pilgrimage. The associated data are required to develop international recommendations and guidelines for TB management and control at mass gathering events.

Big data or bust: realizing the microbial genomics revolution

Pathogen genomics has the potential to transform the clinical and public health management of infectious diseases through improved diagnosis, detection and tracking of antimicrobial resistance and outbreak control. However, the wide-ranging benefits of this technology can only fully be realized through the timely collation, integration and sharing of genomic and clinical/epidemiological metadata by all those involved in the delivery of genomic-informed services. As part of our review on bringing pathogen genomics into ‘health-service’ practice, we undertook extensive stakeholder consultation to examine the factors integral to achieving effective data sharing and integration. Infrastructure tailored to the needs of clinical users, as well as practical support and policies to facilitate the timely and responsible sharing of data with relevant health authorities and beyond, are all essential. We propose a tiered data sharing and integration model to maximize the immediate and longer term utility of microbial genomics in healthcare. Realizing this model at the scale and sophistication necessary to support national and international infection management services is not uncomplicated. Yet the establishment of a clear data strategy is paramount if failures in containing disease spread due to inadequate knowledge sharing are to be averted, and substantial progress made in tackling the dangers posed by infectious diseases.