Epidemiological and genomic landscape of antimicrobial resistance in Malawi

Antimicrobial resistance (AMR) is a global public health problem, which presents a huge threat to the treatment of all forms of bacterial infections. A wide range of bacterial pathogens across the globe are increasingly developing resistance to multiple classes of antimicrobial agents rendering the agents concerned ineffective for the treatment of infections. Bloodstream infection (BSI) and other bacterial infections in sub-Saharan Africa (SSA) and Malawi in particular, are a common cause of morbidity and mortality. Few facilities in SSA however, are able to conduct long-term surveillance and as such the full burden of drug resistant infection (DRI) remain largely unknown across the region. In this thesis, blood cultures routinely taken from adult and paediatric medical patients admitted to Queen Elizabeth Central Hospital (QECH) in Blantyre, Malawi between 1998 and 2016 were analysed to describe trends in BSI and AMR. The analysis revealed a significant decline of BSI in all major pathogens except S. Typhi. However, the majority of isolates were resistant to the Malawian first-line antimicrobial agents (ampicillin, cotrimoxazole and chloramphenicol). Resistance to all the first line antimicrobial agents was more common in Gram-negative pathogens than Gram-positive pathogens. Non-Salmonellae Enterobacteriaceae that produced extended spectrum beta-lactamase (ESBL) and were fluoroquinolone-resistant were detected, and the proportions of these isolates rose significantly during the surveillance. In contrast, a majority of common Gram-positive pathogens remain susceptible to either penicillin or chloramphenicol. Methicillin resistant S. aureus was first reported in 1998 but became regularly detected in the later years of the surveillance. The analysis of blood culture isolates identified E. coli as one of the common causes of BSI in Blantyre, and the proportion of these isolates that were ESBL producers increased over time. Globally, efforts to treat E. coli infections are increasingly being compromised by the rapid, global spread of ESBL-producing E. coli. In this thesis, a whole genome sequencing (WGS) study was carried out to investigate the genetic population structure and molecular determinants of AMR in E. coli isolates from Malawi. Whole genomes of clinical E. coli isolates from patients admitted to QECH were sequenced and analysed using phylogenetic methods and comparative genomics. It was revealed that the E. coli population in Malawi is highly diverse with isolates belonging to five phylogroups, corresponding to five isolate sequence clusters (SCs) that contained over forty sequence types (STs). A unique sub-lineage of ST131 was identified that was distinct from previously defined sub-lineages of this globally disseminated ST. The most common ESBL gene was blaCT X-M-15. Unlike in other settings where presence of the blaCT X-M-15 gene was strongly linked to ST131, here the gene was not lineage-specific suggesting a distinct genomic landscape of ESBL-producing E. coli in Malawi. This thesis also identified Klebsiella spp. isolates as a common cause of BSI in Blantyre, and an increasing proportion of ESBL-producing and fluoroquinolone resistant isolates were identified. The molecular mechanisms and clones of K. pneumoniae associated with ESBL production and fluoroquinolone resistance were yet to be explored in Malawi. Here, a number of K. pneumoniae isolates were selected for WGS, and placed in a global context by comparison with previously sequenced K. pneumoniae isolates from multiple locations outside SSA, in order to identify the molecular determinants of AMR and determine their relationship with K. pneumoniae population structure. Genomic analysis revealed three main lineages of K. pneumoniae, which corresponded to the previously defined KpI, KpII and KpIII lineages. All three lineages exhibited high genetic diversity. Further phylogenetic analysis revealed a sub-lineage of KpI to be a major cause of CA infections in Malawi. The sub-lineage included the clonally related ST14 and ST15 of K. pneumoniae which cause hospital acquired infection in multiple settings across the globe, A large pool of AMR genes, was identified in the genomes of the Malawian isolates, including multiple ESBL and qnr genes. Plasmid-encoded CTX-M-15 was the most common type of ESBL that was identified. In common with E. coli from Malawi, AMR was not restricted to a particular clade of K. pneumoniae. These findings suggest that dissemination of AMR in the K. pneumoniae population in Malawi was either due to a combination of horizontal gene transfer and clonal expansion, or horizontal gene transfer alone. In conclusion, the thesis has shown that ESBL production and fluoroquinolone resistance is rapidly spreading in Malawi across multiple E. coli and K. pneumoniae lineages that are causing increasing levels of infection. As cephalosporins and fluoroquinolones remain the last resort antimicrobial agents in this setting, urgent action is needed to curb the spread of Gram-negative AMR pathogens

Investigating associations between rural-to-urban migration and cardiometabolic disease in Malawi: a population-level study.

BACKGROUND: The extent to which rural-to-urban migration affects risk for cardiometabolic diseases (CMD) in Africa is not well understood. We investigated prevalence and risk for obesity, diabetes, hypertension and precursor conditions by migration status. METHODS: In a cross-sectional survey in Malawi (February 2013-March 2017), 13 903 rural, 9929 rural-to-urban migrant and 6741 urban residents (≥18 years old) participated. We interviewed participants, measured blood pressure and collected anthropometric data and fasting blood samples to estimate population prevalences and odds ratios, using negative binomial regression, for CMD, by migration status. In a sub-cohort of 131 rural-urban siblings-sets, migration-associated CMD risk was explored using conditional Poisson regression. RESULTS: In rural, rural-to-urban migrant and urban residents, prevalence estimates were; 8.9, 20.9 and 15.2% in men and 25.4, 43.9 and 39.3% in women for overweight/obesity; 1.4, 2.9 and 1.9% in men and 1.5, 2.8 and 1.7% in women for diabetes; and 13.4, 18.8 and 12.2% in men and 13.7, 15.8 and 10.2% in women for hypertension. Rural-to-urban migrants had the greatest risk for hypertension (adjusted relative risk for men 1.18; 95% confidence interval 1.04-1.34 and women 1.17: 95% confidence interval 1.05-1.29) and were the most screened, diagnosed and treated for CMD, compared with urban residents. Within sibling sets, rural-to-urban migrant siblings had a higher risk for overweight and pre-hypertension, with no evidence for differences by duration of stay. CONCLUSIONS: Rural-to-urban migration is associated with increased CMD risk in Malawi. In a poor country experiencing rapid urbanization, interventions for the prevention and management of CMD, which reach migrant populations, are needed

Association of shorter leucocyte telomere length with risk of frailty.

BACKGROUND: Frailty is a multidimensional syndrome of decline that affects multiple systems and predisposes to adverse health outcomes. Although chronological age is the major risk factor, inter-individual variation in risk is not fully understood. Leucocyte telomere length (LTL), a proposed marker of biological age, has been associated with risk of many diseases. We sought to determine whether LTL is associated with risk of frailty. METHODS: We utilized cross-sectional data from 441 781 UK Biobank participants (aged 40-69 years), with complete data on frailty indicators and LTL. Frailty was defined as the presence of at least three of five indicators: weaker grip strength, slower walking pace, weight loss in the past year, lower physical activity, and exhaustion in the past 2 weeks. LTL was measured using a validated qPCR method and reported as a ratio of the telomere repeat number (T) to a single-copy gene (S) (T/S ratio). Association of LTL with frailty was evaluated using adjusted (chronological age, sex, deprivation, smoking, alcohol intake, body mass index, and multimorbidity) multinomial and ordinal regression models, and results are presented as relative risk (RRR) or odds ratios (OR), respectively, alongside the 95% confidence interval (CI). Mendelian randomization (MR), using 131 genetic variants associated with LTL, was used to assess if the association of LTL with frailty was causal. RESULTS: Frail participants (4.6%) were older (median age difference (95% CI): 3 (2.5; 3.5) years, P = 2.73 × 10-33 ), more likely to be female (61%, P = 1.97 × 10-129 ), and had shorter LTL (-0.13SD vs. 0.03SD, P = 5.43 × 10-111 ) than non-frail. In adjusted analyses, both age and LTL were associated with frailty (RRR = 1.03 (95% CI: 1.02; 1.04) per year of older chronological age, P = 3.99 × 10-12 ; 1.10 (1.08; 1.11) per SD shorter LTL, P = 1.46 × 10-30 ). Within each age group (40-49, 50-59, 60-69 years), the prevalence of frailty was about 33% higher in participants with shorter (-2SD) versus longer telomeres (+2SD). MR analysis showed an association of LTL with frailty that was directionally consistent with the observational association, but not statistically significant (MR-Median: OR (95% CI): 1.08 (0.98; 1.19) per SD shorter LTL, P = 0.13). CONCLUSIONS: Inter-individual variation in LTL is associated with the risk of frailty independently of chronological age and other risk factors. Our findings provide evidence for an additional biological determinant of frailty.This research has been conducted using the UK Biobank Resource under Application Number 6077. Generation of the LTL measurements was funded by the UK Medical Research Council (MRC), Biotechnology and Biological Sciences Research Council and British Heart Foundation (BHF) through MRC grant MR/M012816/1

Genomic investigation of a suspected Klebsiella pneumoniae outbreak in a neonatal care unit in sub-Saharan Africa.

A special-care neonatal unit from a large public hospital in Malawi was noted as having more frequent, difficult-to-treat infections, and a suspected outbreak of multi-drug-resistant Klebsiella pneumoniae was investigated using genomic characterisation. All K. pneumoniae bloodstream infections (BSIs) from patients in the neonatal ward (n=62), and a subset of K. pneumoniae BSI isolates (n=38) from other paediatric wards in the hospital, collected over a 4 year period were studied. After whole genome sequencing, the strain sequence types (STs), plasmid types, virulence and resistance genes were identified. One ST340 clone, part of clonal complex 258 (CC258) and an ST that drives hospital outbreaks worldwide, harbouring numerous resistance genes and plasmids, was implicated as the likely cause of the outbreak. This study contributes molecular information necessary for tracking and characterizing this important hospital pathogen in sub-Saharan Africa

Early signals of vaccine driven perturbation seen in pneumococcal carriage population genomic data

BACKGROUND: Pneumococcal conjugate vaccines (PCV) have reduced pneumococcal diseases globally. Pneumococcal genomic surveys elucidate PCV effects on population structure but are rarely conducted in low-income settings despite the high disease burden. METHODS:We undertook whole genome sequencing of 660 pneumococcal isolates collected through surveys from healthy carriers two years from PCV14 introduction and one-year post-rollout in northern Malawi. We investigated changes in population structure, within-lineage serotype dynamics, serotype diversity, and frequency of antibiotic resistance (ABR) and accessory genes. RESULTS:In the under-fives, frequency and diversity of vaccine serotypes (VT) decreased significantly post-PCV but no significant changes occurred in over-fives. Clearance of VT serotypes was consistent across different genetic backgrounds (lineages). There was an increase of non-vaccine serotypes (NVT) namely 7C, 15B/C, 23A in under-fives but 28F increased in both age groups. While carriage rates have been recently shown to remain stable post-PCV due replacement serotypes, there was no change in diversity of NVTs. Additionally, frequency of intermediate-penicillin-resistant lineages decreased post-PCV. While frequency of ABR genes remained stable, other accessory genes especially those associated with MGEs and bacteriocins showed changes in frequency post-PCV. CONCLUSIONS:We demonstrate evidence of significant population restructuring post-PCV driven by decreasing frequency of vaccine serotypes and increasing frequency of few NVTs mainly in under-fives. Continued surveillance with WGS remains crucial to fully understand dynamics of the residual VTs and replacement NVT serotypes post-PCV

Shorter leukocyte telomere length is associated with adverse COVID-19 outcomes: A cohort study in UK Biobank.

Background Older age is the most powerful risk factor for adverse coronavirus disease-19 (COVID-19) outcomes. It is uncertain whether leucocyte telomere length (LTL), previously proposed as a marker of biological age, is also associated with COVID-19 outcomes. Methods We associated LTL values obtained from participants recruited into UK Biobank (UKB) during 2006-2010 with adverse COVID-19 outcomes recorded by 30 November 2020, defined as a composite of any of the following: hospital admission, need for critical care, respiratory support, or mortality. Using information on 130 LTL-associated genetic variants, we conducted exploratory Mendelian randomisation (MR) analyses in UKB to evaluate whether observational associations might reflect cause-and-effect relationships. Findings Of 6775 participants in UKB who tested positive for infection with SARS-CoV-2 in the community, there were 914 (13.5%) with adverse COVID-19 outcomes. The odds ratio (OR) for adverse COVID-19 outcomes was 1·17 (95% CI 1·05-1·30; P = 0·004) per 1-SD shorter usual LTL, after adjustment for age, sex and ethnicity. Similar ORs were observed in analyses that: adjusted for additional risk factors; disaggregated the composite outcome and reduced the scope for selection or collider bias. In MR analyses, the OR for adverse COVID-19 outcomes was directionally concordant but non-significant. Interpretation Shorter LTL is associated with higher risk of adverse COVID-19 outcomes, independent of several major risk factors for COVID-19 including age. Further data are needed to determine whether this association reflects causality. Funding UK Medical Research Council, Biotechnology and Biological Sciences Research Council and British Heart Foundation.UK Medical Research Council, Biotechnology and Biological Sciences Research Council and British Heart Foundation

A Novel Air-Dried Multiplex High Resolution Melt Assay for the Detection of Extended Spectrum Beta-Lactamase and Carbapenemase Genes.

OBJECTIVES: This study aimed to develop and evaluate a novel air-dried high-resolution melt (HRM) assay to detect eight major extended spectrum beta-Lactamase (ESBL) (blaSHV and blaCTXM groups 1 and 9) and carbapenemase (blaNDM, blaIMP, blaKPC, blaVIM and blaOXA-48-like) genes that cause antimicrobial resistance to cephalosporins and carbapenems. METHODS: The assay was evaluated using 439 DNA samples extracted from bacterial isolates from Nepal, Malawi and UK and 390 clinical isolates from Nepal with known antimicrobial susceptibility results. Assay reproducibility was evaluated across five different q-PCR instruments (Rotor-Gene Q, QuantStudioTM 5, CFX96, LightCycler® 480 and MIC). Assay stability was also assessed upon the assay storage in the refrigerator (6.2°C±0.9), room temperature (20.4°C±0.7) and oven (29.7°C±1.4) at six time points for eight months. RESULTS: The sensitivity and specificity for detecting the ESBL and carbapenemase genes in comparison to the reference gel-base PCR and sequencing was 94.7% (95%CI: 92.5%-96.5%) and 99.2% (95%CI: 98.8%-99.5%), and 98.5% (95%CI: 97.0%-99.4%) and 98.5% (95%CI: 98.0%-98.9%) when compared to the original HRM wet PCR mix format. The overall agreement was 91.1% (95%CI: 90.0%-92.9%) when predicting phenotypic resistance to cefotaxime and meropenem among Enterobacteriaceae isolates. We observed almost perfect inter-machine reproducibility of the air-dried HRM assay and no loss of sensitivity occurred under all storage conditions and time points. CONCLUSIONS: We present here a ready-to-use air-dried HRM-PCR assay that offers an easy, thermostable, fast and accurate tool for the detection of ESBL and carbapenemase genes in DNA samples to improve AMR

Polygenic basis and biomedical consequences of telomere length variation.

Funder: Health Data Research UK EU/EFPIA Innovative Medicines Initiative Joint Undertaking BigData@Heart (11607).Funder: Health Data Research UKTelomeres, the end fragments of chromosomes, play key roles in cellular proliferation and senescence. Here we characterize the genetic architecture of naturally occurring variation in leukocyte telomere length (LTL) and identify causal links between LTL and biomedical phenotypes in 472,174 well-characterized UK Biobank participants. We identified 197 independent sentinel variants associated with LTL at 138 genomic loci (108 new). Genetically determined differences in LTL were associated with multiple biological traits, ranging from height to bone marrow function, as well as several diseases spanning neoplastic, vascular and inflammatory pathologies. Finally, we estimated that, at the age of 40 years, people with an LTL >1 s.d. shorter than the population mean had a 2.5-year-lower life expectancy compared with the group with ≥1 s.d. longer LDL. Overall, we furnish new insights into the genetic regulation of LTL, reveal wide-ranging influences of LTL on physiological traits, diseases and longevity, and provide a powerful resource available to the global research community

Population genetic structure, antibiotic resistance, capsule switching and evolution of invasive pneumococci before conjugate vaccination in Malawi

INTRODUCTION: Pneumococcal infections cause a high death toll in Sub Saharan Africa (SSA) but the recently rolled out pneumococcal conjugate vaccines (PCV) will reduce the disease burden. To better understand the population impact of these vaccines, comprehensive analysis of large collections of pneumococcal isolates sampled prior to vaccination is required. Here we present a population genomic study of the invasive pneumococcal isolates sampled before the implementation of PCV13 in Malawi. MATERIALS AND METHODS: We retrospectively sampled and whole genome sequenced 585 invasive isolates from 2004 to 2010. We determine the pneumococcal population genetic structure and assessed serotype prevalence, antibiotic resistance rates, and the occurrence of serotype switching. RESULTS: Population structure analysis revealed 22 genetically distinct sequence clusters (SCs), which consisted of closely related isolates. Serotype 1 (ST217), a vaccine-associated serotype in clade SC2, showed highest prevalence (19.3%), and was associated with the highest MDR rate (81.9%) followed by serotype 12F, a non-vaccine serotype in clade SC10 with an MDR rate of 57.9%. Prevalence of serotypes was stable prior to vaccination although there was an increase in the PMEN19 clone, serotype 5 ST289, in clade SC1 in 2010 suggesting a potential undetected local outbreak. Coalescent analysis revealed recent emergence of the SCs and there was evidence of natural capsule switching in the absence of vaccine induced selection pressure. Furthermore, majority of the highly prevalent capsule-switched isolates were associated with acquisition of vaccine-targeted capsules. CONCLUSIONS: This study provides descriptions of capsule-switched serotypes and serotypes with potential to cause serotype replacement post-vaccination such as 12F. Continued surveillance is critical to monitor these serotypes and antibiotic resistance in order to design better infection prevention and control measures such as inclusion of emerging replacement serotypes in future conjugate vaccines