title: Pooling sputum from multiple individuals for Xpert® MTB/RIF testing: a strategy for screening high-risk populations.
abstract: METHODS
  Symptom-based screening for tuberculosis (TB) disease is limited by poor performance of symptom screening in several key populations. We tested the hypothesis that pooling sputum from multiple individuals for Xpert(®) MTB/RIF testing would reduce the number of tests required while retaining an acceptable sensitivity, thus allowing the use of Xpert for TB screening.
  
  
  METHODS
  We compared pooling ratios that would require the least number of assays using Xpert and determined that for a population with a TB prevalence of approximately 3%, a 1:5 pooling ratio is optimal. To evaluate sensitivity, we generated pools of one specimen with known Mycobacterium tuberculosis culture positivity (smear microscopy-positive or -negative) with four culture-negative specimens.
  
  
  RESULTS
  All 20 of the pools generated from a smear- and culture-positive sputum sample were positive using Xpert. Of the 22 pools with a smear-negative, culture-positive sample, we included 17 in the analysis, of which 13 (76%) were Xpert-positive.
  
  
  CONCLUSIONS
  Pooling of sputum samples using Xpert achieved reasonable sensitivity and warrants further evaluation of the systematic screening of high TB prevalence populations.
authors.affiliation: The Aurum Institute, Johannesburg, South Africa.
authors.forename: V
authors.initials: V
authors.lastname: Zishiri
authors.affiliation: The Aurum Institute, Johannesburg, South Africa.
authors.forename: V
authors.initials: V
authors.lastname: Chihota
authors.affiliation: The Aurum Institute, Johannesburg, South Africa.
authors.forename: K
authors.initials: K
authors.lastname: McCarthy
authors.affiliation: The Aurum Institute, Johannesburg, South Africa.
authors.forename: S
authors.initials: S
authors.lastname: Charalambous
authors.affiliation: The Aurum Institute, Johannesburg, South Africa; School of Public Health, University of Witwatersrand, Johannesburg, South Africa.
authors.forename: G J
authors.initials: GJ
authors.lastname: Churchyard
authors.affiliation: The Aurum Institute, Johannesburg, South Africa; Johns Hopkins University School of Medicine, Baltimore, Maryland, USA.
authors.forename: C J
authors.initials: CJ
authors.lastname: Hoffmann
mesh_terms: D024881:Drug Resistance, Bacterial; D006801:Humans; D009169:Mycobacterium tuberculosis / Q000187:drug effects; D011159:Population Surveillance / Q000379:methods*; D015995:Prevalence; D012293:Rifampin / Q000494:pharmacology; D012307:Risk Factors; D012680:Sensitivity and Specificity; D013048:Specimen Handling / Q000379:methods*; D013183:Sputum / Q000382:microbiology*; D018088:Tuberculosis, Multidrug-Resistant / Q000175:diagnosis / Q000453:epidemiology; D014397:Tuberculosis, Pulmonary / Q000175:diagnosis* / Q000453:epidemiology*
chemical_list: D012293:Rifampin