title: Time-to-detection in culture predicts risk of Mycobacterium tuberculosis transmission: a cohort study.
abstract: BACKGROUND
  Contact screening is an essential component of all tuberculosis control strategies. We hypothesize that time-to-detection (TTD) in liquid culture of spontaneously produced sputum samples may help identify index cases at high risk of transmission.
  
  
  METHODS
  We studied retrospectively a cohort of patients with pulmonary tuberculosis in Birmingham, United Kingdom (January 2010-December 2012). We studied the correlation of TTD with the risk of transmission of infection from index cases to contacts and compared this with sputum microscopy. Chest radiographs (CXRs) were graded from 0 to 6 (0, no radiographic evidence of disease; 5, bilateral cavitation; and 6, miliary disease).
  
  
  RESULTS
  Of the 184 cases of pulmonary tuberculosis reported during the study period, 111 were included in the final study, and these generated 825 contacts. A transmission event (new latent or active tuberculosis) was identified in 165 contacts (transmission rate 0.20). Short TTD (<9 days) was associated with an increased risk of transmission (odds ratio, 2.56; P < .001), and this relationship persisted after adjusting for potential confounders. A 1-point increase in CXR grade correlated with a 3.2-day decrease in TTD (P < .001), and this correlation persisted after adjustment for potential confounders.
  
  
  CONCLUSIONS
  TTD < 9 days identifies patients at high risk of transmitting tuberculosis and is superior to sputum smear. CXR grade at diagnosis predicts patients with short TTD. Our findings have the potential to guide the organization and prioritization of contact investigations in similar settings.
authors.affiliation: Department of Infectious Disease and Tropical Medicine, Heartlands Hospital, Birmingham The Jenner Institute, Nuffield Department of Medicine, University of Oxford.
authors.forename: Matthew K
authors.initials: MK
authors.lastname: O'Shea
authors.affiliation: Department of Infectious Disease and Tropical Medicine, Heartlands Hospital, Birmingham Warwick Medical School, University of Warwick, Coventry.
authors.forename: Gavin C K W
authors.initials: GC
authors.lastname: Koh
authors.affiliation: Department of Infectious Disease and Tropical Medicine, Heartlands Hospital, Birmingham Warwick Medical School, University of Warwick, Coventry.
authors.forename: Melinda
authors.initials: M
authors.lastname: Munang
authors.affiliation: Public Health England Regional Centre for Mycobacteriology, West Midlands Public Health Laboratory, Heartlands Hospital.
authors.forename: Grace
authors.initials: G
authors.lastname: Smith
authors.affiliation: Department of Radiology, Heartlands Hospital, Birmingham, United Kingdom.
authors.forename: Arpan
authors.initials: A
authors.lastname: Banerjee
authors.affiliation: Department of Infectious Disease and Tropical Medicine, Heartlands Hospital, Birmingham Warwick Medical School, University of Warwick, Coventry.
authors.forename: Martin
authors.initials: M
authors.lastname: Dedicoat
mesh_terms: D000293:Adolescent; D000328:Adult; D000368:Aged; D000369:Aged, 80 and over; D001431:Bacteriological Techniques; D002648:Child; D002675:Child, Preschool; D015331:Cohort Studies; D016358:Contact Tracing / Q000379:methods; D018562:Disease Transmission, Infectious; D005260:Female; D006801:Humans; D008297:Male; D008853:Microscopy; D008875:Middle Aged; D009169:Mycobacterium tuberculosis / Q000302:isolation & purification*; D013902:Radiography, Thoracic; D012189:Retrospective Studies; D018570:Risk Assessment; D013183:Sputum / Q000382:microbiology; D013997:Time Factors; D014397:Tuberculosis, Pulmonary / Q000175:diagnosis* / Q000635:transmission*; D006113:United Kingdom; D055815:Young Adult
keywords: pulmonary tuberculosis; radiography; time-to-detection; transmission