Suchergebnisse

Antibiotic resistance forms a serious threat to the health of hospitalised patients, rendering otherwise treatable bacterial infections potentially life-threatening. A thorough understanding of the mechanisms by which resistance spreads between patients in different hospitals is required in order to design effective control strategies. We measured the differences between bacterial populations of 52 hospitals in the United Kingdom and Ireland, using whole genome sequences from 1085 MRSA clonal complex 22 isolates collected between 1998 and 2012. The genetic differences between bacterial populations were compared with the number of transferred patients between hospitals and their regional structure. The MRSA populations within single hospitals, regions, and countries were genetically distinct from the rest of the bacterial population at each of these levels. Hospitals from the same patient referral regions showed more similar MRSA populations, as did hospitals sharing many patients. Furthermore, the bacterial population from different time-periods within the same hospital were generally more similar to each other than contemporaneous bacterial populations from different hospitals. We conclude that, while a large part of the dispersal and expansion of MRSA takes place among patients seeking care in single hospitals, inter-hospital spread of resistant bacteria is by no means a rare occurrence. Hospitals are exposed to constant introductions of MRSA on a number of levels: 1) most MRSA is received from hospitals that directly transfer large numbers of patients, while 2) fewer introductions happen between regions or 3) across national borders, reflecting lower numbers of transferred patients. A joint coordinated control effort between hospitals, is therefore paramount for the national control of MRSA, antibiotic-resistant bacteria, and other hospital-associated pathogens. ; This work was supported by grants from the UKCRC Translational Infection Research Initiative, and the Medical Research Council (Grant Number G1000803) with contributions to the Grant from the Biotechnology and Biological Sciences Research Council, the National Institute for Health Research on behalf of the Department of Health, and the Chief Scientist Office of the Scottish Government Health Directorate (to SJP); and by Wellcome Trust grant number 098051 and 089472 awarded to the Wellcome Trust Sanger Institute and BGS respectively. MET is a Clinician Scientist Fellow, supported by the Academy of Medical Sciences and The Health Foundation, and by the NIHR Cambridge Biomedical Research Centre. We thank the British Society of Antimicrobial Chemotherapy (BSAC) bacteraemia resistance surveillance programme for supplying bacterial isolates.

Screening of more than 1,500 drug-resistant strains of Mycobacterium tuberculosis revealed evolutionary patterns characteristic of positive selection for three alanine racemase (Alr) mutations. We investigated these mutations using molecular modeling, in vitro MIC testing, as well as direct measurements of enzymatic activity, which demonstrated that these mutations likely confer resistance to D-cycloserine. ; This work was funded by the University of Otago, Health Research Council Explorer grant and Maurice Wilkins Centre. In addition, parts of this study were supported by the European Union PathoNgenTrace project (grant FP7-278864-2) and the German Center for Infection Research (DZIF). Further funds were received from Fundação para a Ciência e a Tecnologia, Portugal, through the grants UID/Multi/04413/2013 (to M.V. and D.M.), SFRH/BPD/100688/2014 (to D.M.), and SFRH/BPD/95406/2013 (to J.P.). F.C. was supported by the Wellcome Trust 201344/Z/16/Z. T.G.C. was funded by the Medical Research Council UK (grants MR/K000551/1, MR/M01360X/1, and MR/N010469/1). Further support was received the Indian Council of Medical Research, New Delhi and Health Innovation Challenge Fund (grants HICF-T5-342 and WT098600), a parallel funding partnership between the UK Department of Health and the Wellcome Trust. C.U.K. is a research associate at Wolfson College, Cambridge, UK. K.L.K., Y.N., and H.K.O.-R. have received funding for alanine racemase-related projects from L2 Diagnostics LLC, New Haven, CT. J.P., S.J.P., and C.U.K. have collaborated with Illumina, Inc. on a number of scientific projects. J.P. has received funding for travel and accommodation from Pacific Biosciences, Inc. and Illumina, Inc. S.J.P. has received funding for travel and accommodation from Illumina, Inc. C.U.K. is a consultant for the Foundation for Innovative New Diagnostics. The Bill & Melinda Gates Foundation and Janssen Pharmaceutica covered C.U.K.'s travel and accommodation to present at meetings. The European Society of Mycobacteriology awarded C.U.K. and M.M. the Gertrud Meissner Award, which is sponsored by Hain Lifescience.

To the Editor: Previously, we reported the use of whole-genome sequencing to investigate a putative methicillin-resistant Staphylococcus aureus (MRSA) outbreak in 2011 in the special care baby unit (SCBU) at the Cambridge University Hospitals National Health Service Foundation Trust (CUH) in the United Kingdom (1). The report identified 26 related cases of infection with or asymptomatic carriage of MRSA and showed that transmission occurred within the SCBU, between mothers on a postnatal ward, and in the community; the outbreak apparently resolved at the end of 2011. The outbreak strain, sequence type (ST) 2371, was of a novel multilocus ST related to the dominant hospital-associated lineage in the UK (ST22, EMRSA-15), but unlike most ST22 strains, this strain was Panton-Valentine leucocidin–positive (2). Since then, ST2371 has been identified as a prevalent communityassociated MRSA clone in Southern India, and sporadic isolates have also been detected by whole-genome sequencing of MRSA in Denmark (3–5) ; The study was supported by grants from the UKCRC Translational Infection Research (TIR) Initiative, and the Medical Research Council (Grant Number G1000803) with contributions to the Grant from the Biotechnology and Biological Sciences Research Council, the National Institute for Health Research on behalf of the Department of Health, and the Chief Scientist Office of the Scottish Government Health Directorate (to Prof. Peacock); by a Healthcare Infection Society Major Research Grant; and by Wellcome Trust grant number 098051 awarded to the Wellcome Trust Sanger Institute.

$\textit{Staphylococcus aureus}$ carriers are at higher risk of $\textit{S. aureus}$ infection and are a reservoir for transmission to others. Detection of nasal $\textit{S. aureus}$ carriage is important for both targeted decolonization and epidemiological studies. Self-administered nasal swabbing has been reported previously, but the effects of posting swabs prior to culture on $\textit{S. aureus}$ yield have not been investigated. A longitudinal cohort study was performed in which healthy volunteers were recruited, trained in the swabbing procedure and asked to take weekly nasal swabs for 6 weeks (median: 3 weeks, range 1-6 weeks). Two swabs were taken at each sampling episode and randomly assigned for immediate processing on arrival to the laboratory (Swab A) or second class postage prior to processing (Swab B). $\textit{S. aureus}$ was isolated using standard methods. A total of 95 participants were recruited, who took 944 swabs (472 pairs) over a median of 5 weeks. Of these, 459 swabs were positive for $\textit{S. aureus}$. We found no significant difference (P=0.25) between 472 pairs of nasal self-swabs processed immediately or following standard postage from 95 study participants (51.4 % vs. 48.6 %, respectively). We also provide further evidence that persistent carriers can be detected by two weekly swabs with high degrees of sensitivity [92.3 % (95 % CI 74.8-98.8 %)] and specificity [95.6 % (95 % CI 84.8-99.3 %)] compared with a gold standard of five weekly swabs. Self-swabbing and postage of nasal swabs prior to processing has no effect on yield of $\textit{S. aureus}$, and could facilitate large community-based carriage studies. ; This work was supported by UKCRC Translational Infection Research (TIR) Initiative and the Medical Research Council (Grant Number G1000803) with contributions to the Grant from the Biotechnology and Biological Sciences Research Council, the National Institute for Health Research on behalf of the Department of Health, and the Chief Scientist Office of the Scottish Government Health Directorate and by a Medical Research Council Partnership grant (G1001787/1) held between the Department of Veterinary Medicine, University of Cambridge (M. A. H.), the School of Clinical Medicine, University of Cambridge (S. J. P.), the Moredun Research Institute and the Wellcome Trust Sanger Institute.

BACKGROUND: Whole-genome sequencing (WGS) has typically been used to confirm or refute hospital/ward outbreaks of methicillin-resistant Staphylococcus aureus (MRSA) identified through routine practice. However, appropriately targeted WGS strategies that identify routinely 'undetectable' transmission remains the ultimate aim. METHODS: WGS of MRSA isolates sent to a regional microbiological laboratory was performed as part of a 12-month prospective observational study. Phylogenetic analyses identified a genetically-related cluster of E-MRSA15 isolated from patients registered to the same General Practice (GP) surgery. This led to an investigation to identify epidemiological links, find additional cases and determine potential for on-going transmission. RESULTS: We identified 15 MRSA-positive individuals with 27 highly-related MRSA isolates who were linked to the GP surgery, two of whom died with MRSA bacteremia. Of the 13 cases who were further investigated, 11 had attended a leg ulcer/podiatry clinic. Cases lacked epidemiological links to hospitals, suggesting that transmission occurred elsewhere. Environmental and staff screening at the GP surgery did not identify an on-going source of infection. CONCLUSIONS: Surveillance in the United Kingdom shows that the proportion of MRSA bacteremias apportioned to hospitals is decreasing, suggesting the need for greater focus on the detection of MRSA outbreaks and transmission in the community. This case study confirms that the typically nosocomial lineage (E-MRSA15) can transmit within community settings. Our study exemplifies the continued importance of WGS in detecting outbreaks including those which may be missed by routine practice, and suggests that universal WGS of bacteremia isolates may help detect outbreaks in low-surveillance settings. ; This work was supported by grants from the UK Clinical Research Collaboration Translational Infection Research Initiative, and the Medical Research Council (Grant Number G1000803) with contributions to the Grant from the Biotechnology and Biological Sciences Research Council, the National Institute for Health Research on behalf of the Department of Health, and the Chief Scientist Office of the Scottish Government Health Directorate (to Prof. Peacock); by a Healthcare Infection Society Major Research Grant (to Prof. Peacock), and by Wellcome Trust grant number 098051 awarded to the Wellcome Trust Sanger Institute. MST was a Wellcome Trust Clinical PhD Fellow. FC was supported by the Wellcome Trust (201344/Z/16/Z). These sponsors of the study had no role in study design, data collection, data analysis, data interpretation, or writing of the report. The public health investigation was supported by Public Health England.

BACKGROUND: Melioidosis, an often fatal infectious disease in Northeast Thailand, is caused by skin inoculation, inhalation or ingestion of the environmental bacterium, Burkholderia pseudomallei. The major underlying risk factor for melioidosis is diabetes mellitus. Recommendations for melioidosis prevention include using protective gear such as rubber boots and gloves when in direct contact with soil and environmental water, and consuming bottled or boiled water. Only a small proportion of people follow such recommendations. METHODS: Nine focus group discussions were conducted to evaluate barriers to adopting recommended preventive behaviours. A total of 76 diabetic patients from northeast Thailand participated in focus group sessions. Barriers to adopting the recommended preventive behaviours and future intervention strategies were identified using two frameworks: the Theoretical Domains Framework and the Behaviour Change Wheel. RESULTS: Barriers were identified in the following five domains: (i) knowledge, (ii) beliefs about consequences, (iii) intention and goals, (iv) environmental context and resources, and (v) social influence. Of 76 participants, 72 (95%) had never heard of melioidosis. Most participants saw no harm in not adopting recommended preventive behaviours, and perceived rubber boots and gloves to be hot and uncomfortable while working in muddy rice fields. Participants reported that they normally followed the behaviour of friends, family and their community, the majority of whom did not wear boots while working in rice fields and did not boil water before drinking. Eight intervention functions were identified as relevant for the intervention: (i) education, (ii) persuasion, (iii) incentivisation, (iv) coercion, (v) modeling, (vi) environmental restructuring, (vii) training, and (viii) enablement. Participants noted that input from role models in the form of physicians, diabetic clinics, friends and families, and from the government via mass media would be required for them to change their behaviours. CONCLUSION: There are numerous barriers to the adoption of behaviours recommended for melioidosis prevention. We recommend that a multifaceted intervention at community and government level is required to achieve the desired behaviour changes.

Livestock-associated methicillin-resistant Staphylococcus aureus (LA-MRSA) is an emerging problem in many parts of the world. LA-MRSA has been isolated previously from animals and humans in the United Kingdom (UK), but the prevalence is unknown. The aim of this study was to determine the prevalence and to describe the molecular epidemiology of LA-MRSA isolated in the East of England (broadly Cambridge and the surrounding area). We accessed whole genome sequence data for 2,283 MRSA isolates from 1,465 people identified during a 12-month prospective study between 2012 and 2013 conducted in the East of England, United Kingdom. This laboratory serves four hospitals and 75 general practices. We screened the collection for multilocus sequence types (STs) and for host specific resistance and virulence factors previously associated with LA-MRSA. We identified 13 putative LA-MRSA isolates from 12 individuals, giving an estimated prevalence of 0.82% (95% CI 0.47% to 1.43%). Twelve isolates were mecC-MRSA (ten CC130, one ST425 and one ST1943) and single isolate was ST398. Our data demonstrate a low burden of LA-MRSA in the East of England, but the detection of mecC-MRSA and ST398 indicates the need for vigilance. Genomic surveillance provides a mechanism to detect and track the emergence and spread of MRSA clones of human importance. ; Supported by grants from the UKCRC Translational Infection Research (TIR) Initiative, and the Medical Research Council (Grant Number G1000803) with contributions to the Grant from the Biotechnology and Biological Sciences Research Council, the National Institute for Health Research on behalf of the Department of Health, and the Chief Scientist Ofce of the Scottish Government Health Directorate (to Prof. Peacock); a Hospital Infection Society Major Research Grant, and by Wellcome Trust grant number 098051 awarded to the Wellcome Trust Sanger Institute. Tis work was supported by the Wellcome Trust 201344/Z/16/Z. M.E.T. is a Clinician Scientist Fellow, supported by the Academy of Medical Sciences and the Health Foundation, and by the NIHR Cambridge Biomedical Research Centre.

This work was supported by UKCRC Translational Infection Research (TIR) Initiative, and the Medical Research Council (Grant Number G1000803) with contributions to the Grant from the Biotechnology and Biological Sciences Research Council, the National Institute for Health Research on behalf of the Department of Health, and the Chief Scientist Office of the Scottish Government Health Directorate and by a Medical Research Council Partnership grant (G1001787/1) held between the Department of Veterinary Medicine, University of Cambridge (M.A.H.), the School of Clinical Medicine, University of Cambridge (S.J.P.), the Moredun Research Institute and the Wellcome Trust Sanger Institute. ; This is the final version of the article. It first appeared from Oxford University Press via http://dx.doi.org/10.1093/jac/dkv317

Background: Horizontal transfer of mobile genetic elements (MGEs) that carry virulence and antimicrobial resistance genes mediates the evolution of methicillin-resistant Staphylococcus aureus, and the emergence of new MRSA clones. Most MRSA lineages show an association with specific MGEs and the evolution of MGE composition following clonal expansion has not been widely studied. Results: We investigated the genomes of 1193 S. aureus bloodstream isolates, 1169 of which were MRSA, collected in the UK and the Republic of Ireland between 2001 and 2010. The majority of isolates belonged to clonal complex (CC)22 (n=923), which contained diverse MGEs including elements that were found in other MRSA lineages. Several MGEs showed variable distribution across the CC22 phylogeny, including two antimicrobial resistance plasmids (pWBG751-like and SAP078A-like, carrying erythromycin and heavy metal resistance genes, respectively), a pathogenicity island carrying the enterotoxin C gene and two phage types Sa1int and Sa6int. Multiple gains and losses of these five MGEs were identified in the CC22 phylogeny using ancestral state reconstruction. Analysis of the temporal distribution of the five MGEs between 2001 and 2010 revealed an unexpected reduction in prevalence of the two plasmids and the pathogenicity island, and an increase in the two phage types. This occurred across the lineage and was not correlated with changes in the relative prevalence of CC22, or of any sub-lineages within in. Conclusions: Ancestral state reconstruction coupled with temporal trend analysis demonstrated that epidemic MRSA CC22 has an evolving MGE composition, and indicates that this important MRSA lineage has continued to adapt to changing selective pressure since its emergence. ; The study was funded by grants from the UKCRC Translational Infection Research Initiative, and the Medical Research Council (grant no. G1000803) with contributions to the grant from the Biotechnology and Biological Sciences Research Council (BBSRC), the National Institute for Health Research on behalf of the Department of Health, and the Chief Scientist Office of the Scottish Government Health Directorate (to SJP). DJ, SRH and JP are funded by the Wellcome Trust grant 098051. FC is funded by the Wellcome Trust grant 201,344/Z/16/Z. AEM is funded by BBSRC grant BB/M014088/1. MET is a Clinician Scientist Fellow funded by the Academy of Medical Sciences and The Health Foundation and supported by the NIHR Cambridge Biomedical Research Centre. In all cases the funders were not involved in any aspect of the design of the study and collection, analysis, and interpretation of data and in writing the manuscript.

BACKGROUND: The spread of USA300 methicillin-resistant Staphylococcus aureus (MRSA) across the United States resulted in an epidemic of infections. In Europe, only sporadic cases or small clusters of USA300 infections are described, and its prevalence in England is unknown. We conducted prospective surveillance for USA300 in the east of England. METHODS: We undertook a 12-month prospective observational cohort study of all individuals with MRSA isolated from community and hospital samples submitted to a microbiology laboratory. At least 1 MRSA isolate from each individual underwent whole-genome sequencing. USA300 was identified on the basis of sequence analysis, and phylogenetic comparisons were made between these and USA300 genomes from the United States. RESULTS: Between April 2012 and April 2013, we sequenced 2283 MRSA isolates (detected during carriage screening and in clinical samples) from 1465 individuals. USA300 was isolated from 24 cases (1.6%). Ten cases (42%) had skin and soft tissue infection, and 2 cases had invasive disease. Phylogenetic analyses identified multiple introductions and household transmission of USA300. CONCLUSIONS: Use of a diagnostic laboratory as a sentinel for surveillance has identified repeated introductions of USA300 in eastern England in 2012-2013, with evidence for limited transmission. Our results show how systematic surveillance could provide an early warning of strain emergence and dissemination. ; This work was supported by grants from the UK Clinical Research Collaboration Translational Infection Research Initiative, and the Medical Research Council (Grant Number G1000803) with contributions to the Grant from the Biotechnology and Biological Sciences Research Council, the National Institute for Health Research on behalf of the Department of Health, and the Chief Scientist Office of the Scottish Government Health Directorate (to Prof. Peacock); by a Healthcare Infection Society Major Research Grant (to Prof. Peacock), and by Wellcome Trust grant number 098051 awarded to the Wellcome Trust Sanger Institute. MST is a Wellcome Trust Clinical PhD Fellow. MET is a Clinician Scientist Fellow, supported by the Academy of Medical Sciences and the Health Foundation, and by the National Institute for Health Research Cambridge Biomedical Research Centre. ; This is the final version of the article. It first appeared from Oxford University Press via https://doi.org/10.1093/infdis/jiw166

Clinical cases of melioidosis caused by the saprophyte Burkholderia pseudomallei were first noted in the Lao People's Democratic Republic (PDR) in 1999. In this study, 36% of 110 soil samples in northern Lao PDR were positive for B. pseudomallei, providing further evidence for the presence of melioidosis in this country.

Melioidosis is a major cause of morbidity and mortality in Southeast Asia, where the causative organism (Burkholderia pseudomallei) is present in the soil. In the Lao People's Democratic Republic (Laos), B. pseudomallei is a significant cause of sepsis around the capital, Vientiane, and has been isolated in soil near the city, adjacent to the Mekong River. We explored whether B. pseudomallei occurs in Lao soil distant from the Mekong River, drawing three axes across northwest, northeast, and southern Laos to create nine sampling areas in six provinces. Within each sampling area, a random rice field site containing a grid of 100 sampling points each 5 m apart was selected. Soil was obtained from a depth of 30 cm and cultured for B. pseudomallei. Four of nine sites (44%) were positive for B. pseudomallei, including all three sites in Saravane Province, southern Laos. The highest isolation frequency was in east Saravane, where 94% of soil samples were B. pseudomallei positive with a geometric mean concentration of 464 CFU/g soil (95% confidence interval, 372 to 579 CFU/g soil; range, 25 to 10,850 CFU/g soil). At one site in northwest Laos (Luangnamtha), only one sample (1%) was positive for B. pseudomallei, at a concentration of 80 CFU/g soil. Therefore, B. pseudomallei occurs in Lao soils beyond the immediate vicinity of the Mekong River, alerting physicians to the likelihood of melioidosis in these areas. Further studies are needed to investigate potential climatic, soil, and biological determinants of this heterogeneity.

Several candidates for a vaccine against Burkholderia pseudomallei, the causal bacterium of melioidosis, have been developed, and a rational approach is now needed to select and advance candidates for testing in relevant nonhuman primate models and in human clinical trials. Development of such a vaccine was the topic of a meeting in the United Kingdom in March 2014 attended by international candidate vaccine developers, researchers, and government health officials. The focus of the meeting was advancement of vaccines for prevention of natural infection, rather than for protection from the organism's known potential for use as a biological weapon. A direct comparison of candidate vaccines in well-characterized mouse models was proposed. Knowledge gaps requiring further research were identified. Recommendations were made to accelerate the development of an effective vaccine against melioidosis.

OBJECTIVES: Infectious diseases consultation (IDC) in adults with Staphylococcus aureus bacteraemia (SAB) has been shown to improve management and outcome. The aim of this study was to evaluate the impact of IDC on the management of SAB in children. STUDY DESIGN: Observational cohort study of children with SAB. SETTING: Cambridge University Hospitals National Health Service (NHS) Foundation Trust, a large acute NHS Trust in the UK. PARTICIPANTS: All children with SAB admitted to the Cambridge University Hospitals NHS Foundation Trust between 16 July 2006 and 31 December 2012. METHODS: Children with SAB between 2006 and 31 October 2009 were managed by routine clinical care (pre-IDC group) and data were collected retrospectively by case notes review. An IDC service for SAB was introduced in November 2009. All children with SAB were reviewed regularly and data were collected prospectively (IDC group) until 31 December 2012. Baseline characteristics, quality metrics and outcome were compared between the pre-IDC group and IDC group. RESULTS: There were 66 episodes of SAB in 63 children-28 patients (30 episodes) in the pre-IDC group, and 35 patients (36 episodes) in the IDC group. The median age was 3.4 years (IQR 0.2-10.7 years). Patients in the IDC group were more likely to have echocardiography performed, a removable focus of infection identified and to receive a longer course of intravenous antimicrobial therapy. There were no differences in total duration of antibiotic therapy, duration of hospital admission or outcome at 30 or 90 days following onset of SAB. CONCLUSIONS: IDC resulted in improvements in the investigation and management of SAB in children. ; This work was supported by grants from the UK Clinical Research Collaboration (UKCRC) Translational Infection Research Initiative (TIRI); the Medical Research Council (G1000803), with contributions from the Biotechnology and Biological Sciences Research Council, the National Institute for Health Research (NIHR) on behalf of the UK Department of Health, and the Chief Scientist of the Scottish Government Health Directorate; the Public Health England; and the NIHR Cambridge Biomedical Research Centre.

BackgroundMandatory reporting of methicillin-resistant Staphylococcus aureus (MRSA) bloodstream infections (BSI) has occurred in England for over 15years. Epidemiological information is recorded, but routine collection of isolates for characterisation has not been routinely undertaken. Ongoing developments in whole-genome sequencing (WGS) have demonstrated its value in outbreak investigations and for determining the spread of antimicrobial resistance and bacterial population structure. Benefits of adding genomics to routine epidemiological MRSA surveillance are unknown.AimTo determine feasibility and potential utility of adding genomics to epidemiological surveillance of MRSA.MethodsWe conducted an epidemiological and genomic survey of MRSA BSI in England over a 1-year period (1 October 2012--30 September 2013).ResultsDuring the study period, 903 cases of MRSA BSI were reported; 425 isolates were available for sequencing of which, 276 (65%) were clonal complex (CC) 22. Addition of 64 MRSA genomes from published outbreak investigations showed that the study genomes could provide context for outbreak isolates and supported cluster identification. Comparison to other MRSA genome collections demonstrated variation in clonal diversity achieved through different sampling strategies and identified potentially high-risk clones e.g. USA300 and local expansion of CC5 MRSA in South West England.ConclusionsWe demonstrate the potential utility of combined epidemiological and genomic MRSA BSI surveillance to determine the national population structure of MRSA, contextualise previous MRSA outbreaks, and detect potentially high-risk lineages. These findings support the integration of epidemiological and genomic surveillance for MRSA BSI as a step towards a comprehensive surveillance programme in England. ; This work was supported by grants from the UK Clinical Research Collaboration Translational Infection Research Initiative, and the Medical Research Council (Grant Number G1000803) with contributions to the Grant from the Biotechnology and Biological Sciences Research Council, the National Institute for Health Research on behalf of the Department of Health, and the Chief Scientist Office of the Scottish Government Health Directorate (to Prof. Peacock); and the Wellcome Trust (to Prof. Parkhill [Grant 098051], Prof. Peacock). MST is a Wellcome Trust Clinical PhD Fellow at the University of Cambridge. MET is a Clinician Scientist Fellow, supported by the Academy of Medical Sciences and the Health Foundation, and by the National Institute for Health Research Cambridge Biomedical Research Centre. FC is supported by the Wellcome Trust (201344/Z/16/Z).