title: Increased detection of smear-negative pulmonary tuberculosis by GeneXpert MTB/RIF® assay after bleach concentration.
abstract: The GeneXpert MTB/RIF assay (Xpert) was endorsed as the initial diagnostic tool in people suspected of human immunodeficiency virus-associated or drug-resistant tuberculosis (TB). However, information regarding the performance of Xpert for diagnosing smear-negative TB in high burden settings remains limited. We evaluated the diagnostic accuracy of Xpert and the impact of bleach concentration on the performance of Xpert using smear-negative sputum samples from human immunodeficiency virus-negative patients.
  
  
  
  One spot and one morning smear-negative sputum samples per patient were examined using Xpert and culture at the Mycobacteriology Research Center of Jimma University, Ethiopia. The sputum culture on both Löwenstein-Jensen and/or Mycobacteria Growth Indicator Tube was the gold-standard.
  
  
  
  Of 185 smear-negative presumptive pulmonary TB cases, 19 (10.3%) had culture-proven TB. The sensitivity of Xpert on spot and morning sputum was similar (63.2%). Testing two specimens per patient insignificantly increased the sensitivity of Xpert. Bleach concentration and pelleting improved the sensitivity of Xpert over unprocessed sputum in paired samples (73.8% vs. 63.2%) without affecting the specificity (95%). Bleach concentration and pelleting allowed an additional seven cases of TB (missed on the first and second direct Xperts) to be detected, five of which were from culture-negative cases.
  
  
  
  Testing of a single sputum sample by Xpert can reach reasonable sensitivity and results would be available on the same day, avoiding loss of patients and treatment delay. The sensitivity of Xpert was improved after bleach concentration and pelleting, although its added value needs further study on a larger scale.
authors.affiliation: Mycobacteriology Research Center, Institute of Biotechnology Research, Jimma University, Jimma, Ethiopia; Department of Medical Laboratory Sciences and Pathology, Jimma University, Jimma, Ethiopia; Department of Biomedical Sciences, University of Antwerp, Antwerp, Belgium. Electronic address: mulualemt.tadesse@gmail.com.
authors.forename: Mulualem
authors.initials: M
authors.lastname: Tadesse
authors.affiliation: Mycobacteriology Research Center, Institute of Biotechnology Research, Jimma University, Jimma, Ethiopia; Department of Medical Laboratory Sciences and Pathology, Jimma University, Jimma, Ethiopia.
authors.forename: Dossegnaw
authors.initials: D
authors.lastname: Aragaw
authors.affiliation: Department of Biomedical Sciences, University of Antwerp, Antwerp, Belgium; Mycobacteriology Unit, Department of Microbiology, Institute of Tropical Medicine, Antwerp, Belgium.
authors.forename: Leen
authors.initials: L
authors.lastname: Rigouts
authors.affiliation: Mycobacteriology Research Center, Institute of Biotechnology Research, Jimma University, Jimma, Ethiopia; Department of Medical Laboratory Sciences and Pathology, Jimma University, Jimma, Ethiopia.
authors.forename: Gemeda
authors.initials: G
authors.lastname: Abebe
mesh_terms: D000328:Adult; D000904:Antibiotics, Antitubercular / Q000494:pharmacology; D057886:Bleaching Agents / Q000032:analysis; D003955:Diagnostic Tests, Routine / Q000295:instrumentation / Q000379:methods*; D005260:Female; D006801:Humans; D008297:Male; D008875:Middle Aged; D009169:Mycobacterium tuberculosis / Q000187:drug effects / Q000235:genetics / Q000302:isolation & purification*; D011446:Prospective Studies; D012293:Rifampin / Q000494:pharmacology; D012973:Sodium Hypochlorite / Q000032:analysis; D013183:Sputum / Q000382:microbiology; D014397:Tuberculosis, Pulmonary / Q000175:diagnosis* / Q000382:microbiology; D055815:Young Adult
chemical_list: D000904:Antibiotics, Antitubercular; D057886:Bleaching Agents; D012973:Sodium Hypochlorite; D012293:Rifampin
keywords: Bleach concentration; Diagnostic accuracy; Smear-negative tuberculosis; Xpert MTB/RIF