title: Blood culture-PCR to optimise typhoid fever diagnosis after controlled human infection identifies frequent asymptomatic cases and evidence of primary bacteraemia.
abstract: Improved diagnostics for typhoid are needed; a typhoid controlled human infection model may accelerate their development and translation. Here, we evaluated a blood culture-PCR assay for detecting infection after controlled human infection with S. Typhi and compared test performance with optimally performed blood cultures.
  
  
  
  Culture-PCR amplification of blood samples was performed alongside daily blood culture in 41 participants undergoing typhoid challenge. Study endpoints for typhoid diagnosis (TD) were fever and/or bacteraemia. Overall, 24/41 (59%) participants reached TD, of whom 21/24 (86%) had ≥1 positive blood culture (53/674, 7.9% of all cultures) or 18/24 (75%) had ≥1 positive culture-PCR assay result (57/684, 8.3%). A further five non-bacteraemic participants produced culture-PCR amplicons indicating infection; overall sensitivity/specificity of the assay compared to the study endpoints were 70%/65%. We found no significant difference between blood culture and culture-PCR methods in ability to identify cases (12 mismatching pairs, p = 0.77, binomial test). Clinical and stool culture metadata demonstrated that additional culture-PCR amplification positive individuals likely represented true cases missed by blood culture, suggesting the overall attack rate may be 30/41 (73%) rather than 24/41 (59%). Several participants had positive culture-PCR results soon after ingesting challenge providing new evidence for occurrence of an early primary bacteraemia.
  
  
  
  Overall the culture-PCR assay performed well, identifying extra typhoid cases compared with routine blood culture alone. Despite limitations to widespread field-use, the benefits of increased diagnostic yield, reduced blood volume and faster turn-around-time, suggest that this assay could enhance laboratory typhoid diagnostics in research applications and high-incidence settings.
authors.affiliation: Oxford Vaccine Group, Department of Paediatrics and the NIHR Oxford Biomedical Research Centre, University of Oxford, Oxford, United Kingdom; The Hospital for Tropical Diseases, Wellcome Trust Major Overseas Programme, Oxford University Clinical Research Unit, Ho Chi Minh City, Viet Nam. Electronic address: thomas.darton@paediatrics.ox.ac.uk.
authors.forename: Thomas C
authors.initials: TC
authors.lastname: Darton
authors.affiliation: Oxford Vaccine Group, Department of Paediatrics and the NIHR Oxford Biomedical Research Centre, University of Oxford, Oxford, United Kingdom.
authors.forename: Liqing
authors.initials: L
authors.lastname: Zhou
authors.affiliation: Oxford Vaccine Group, Department of Paediatrics and the NIHR Oxford Biomedical Research Centre, University of Oxford, Oxford, United Kingdom.
authors.forename: Christoph J
authors.initials: CJ
authors.lastname: Blohmke
authors.affiliation: Oxford Vaccine Group, Department of Paediatrics and the NIHR Oxford Biomedical Research Centre, University of Oxford, Oxford, United Kingdom.
authors.forename: Claire
authors.initials: C
authors.lastname: Jones
authors.affiliation: Oxford Vaccine Group, Department of Paediatrics and the NIHR Oxford Biomedical Research Centre, University of Oxford, Oxford, United Kingdom.
authors.forename: Claire S
authors.initials: CS
authors.lastname: Waddington
authors.affiliation: The Hospital for Tropical Diseases, Wellcome Trust Major Overseas Programme, Oxford University Clinical Research Unit, Ho Chi Minh City, Viet Nam; Centre for Tropical Medicine and Global Health, Nuffield Department of Clinical Medicine, Oxford University, Oxford, United Kingdom.
authors.forename: Stephen
authors.initials: S
authors.lastname: Baker
authors.affiliation: Oxford Vaccine Group, Department of Paediatrics and the NIHR Oxford Biomedical Research Centre, University of Oxford, Oxford, United Kingdom.
authors.forename: Andrew J
authors.initials: AJ
authors.lastname: Pollard
mesh_terms: D000293:Adolescent; D000328:Adult; D058345:Asymptomatic Infections / Q000453:epidemiology; D016470:Bacteremia / Q000145:classification / Q000175:diagnosis* / Q000382:microbiology; D000071997:Blood Culture; D003470:Culture Media / Q000737:chemistry; D004269:DNA, Bacterial / Q000097:blood*; D005260:Female; D005334:Fever / Q000209:etiology / Q000382:microbiology; D064368:Healthy Volunteers; D006801:Humans; D008297:Male; D008875:Middle Aged; D016133:Polymerase Chain Reaction / Q000379:methods*; D012485:Salmonella typhi / Q000302:isolation & purification*; D012680:Sensitivity and Specificity; D014435:Typhoid Fever / Q000097:blood / Q000175:diagnosis*; D055815:Young Adult
chemical_list: D003470:Culture Media; D004269:DNA, Bacterial
keywords: Controlled human infection model; Diagnostics; Febrile disease; Polymerase chain reaction; Salmonella Typhi; Typhoid fever