title: High yield of culture-based diagnosis in a TB-endemic setting.
abstract: BACKGROUND
  In most of the world, microbiologic diagnosis of tuberculosis (TB) is limited to microscopy. Recent guidelines recommend culture-based diagnosis where feasible.
  
  
  METHODS
  In order to evaluate the relative and absolute incremental diagnostic yield of culture-based diagnosis in a high-incidence community in Cape Town, South Africa, subjects evaluated for suspected TB had their samples processed for microscopy and culture over a 21 month period.
  
  
  RESULTS
  For 2537 suspect episodes with 2 smears and 2 cultures done, 20.0% (508) had at least one positive smear and 29.9% (760) had at least one positive culture. One culture yielded 1.8 times more cases as 1 smear (relative yield), or an increase of 12.0% (absolute yield). Based on the latter value, the number of cultures needed to diagnose (NND) one extra case of TB was 8, compared to 19 if second specimens were submitted for microscopy.
  
  
  CONCLUSIONS
  In a high-burden setting, the introduction of culture can markedly increase TB diagnosis over microscopy. The concept of number needed to diagnose can help in comparing incremental yield of diagnosis methods. Although new promising diagnostic molecular methods are being implemented, TB culture is still the gold standard.
authors.affiliation: Department of Medicine, McGill University, Montreal, Québec, Canada. marcel.behr@mcgill.ca
authors.forename: Anne-Marie
authors.initials: AM
authors.lastname: Demers
authors.forename: Suzanne
authors.initials: S
authors.lastname: Verver
authors.forename: Andrew
authors.initials: A
authors.lastname: Boulle
authors.forename: Robin
authors.initials: R
authors.lastname: Warren
authors.forename: Paul
authors.initials: P
authors.lastname: van Helden
authors.forename: Marcel A
authors.initials: MA
authors.lastname: Behr
authors.forename: David
authors.initials: D
authors.lastname: Coetzee
mesh_terms: D000328:Adult; D001431:Bacteriological Techniques / Q000379:methods*; D005260:Female; D006801:Humans; D008297:Male; D008853:Microscopy / Q000379:methods; D008875:Middle Aged; D009169:Mycobacterium tuberculosis / Q000254:growth & development / Q000302:isolation & purification*; D012680:Sensitivity and Specificity; D013019:South Africa; D014376:Tuberculosis / Q000175:diagnosis*