title: Diagnosis of tuberculosis by using a nucleic acid amplification test in an urban population with high HIV prevalence in the United States.
abstract: BACKGROUND
  Use of nucleic acid amplification tests (NAAT) for the diagnosis of Mycobacterium tuberculosis (TB) has been recommended on respiratory specimens submitted for acid-fast bacilli (AFB) testing. It also helps distinguish between TB and non-tuberculous mycobacteria (NTM) species in a setting where NTM rates are relatively high. The purposes of this study are to describe the trend and characteristics of all AFB smear-positive respiratory samples that underwent amplified Mycobacterium tuberculosis direct (MTD) testing, a type of NAAT, and to evaluate the clinical utility and necessity of the test for diagnosis of TB in a population with high-HIV prevalence.
  
  
  METHODS
  Prospective diagnostic testing and retrospective data analyses were conducted on all AFB smear-positive respiratory samples that underwent MTD testing from 2001 to 2011 at Grady Memorial Hospital (GMH), Atlanta, USA. The test performance was compared to culture.
  
  
  RESULTS
  A total of 2,240 AFB smear-positive specimens from 1,412 patients were tested and analyzed in the study. The proportion of specimens that were culture-positive for TB was 28.5%. Sensitivity, specificity, positive predictive value, and negative predictive value of the MTD were 99.0%, 98.0%, 95.3% and 99.6%, respectively. A downward trend was observed in the yearly numbers as well as the proportions of MTD-positive specimens during the study period (p<0.01). There were 2,027 (90.5%) specimens from patients with known HIV status, of which 70.6% was HIV positive and the majority of them (81.8%) had CD4 counts of less than 200 cells/µL. HIV-positives were more likely to have NTM compared to HIV negatives (67.7% vs. 35.4%, p<0.01).
  
  
  CONCLUSIONS
  Despite the decrease in the incidence of TB, NAAT continues to be an accurate and important diagnostic test in a population with high HIV prevalence, and it differentiates TB and NTM organisms.
authors.affiliation: Department of Medicine, Emory University School of Medicine, Atlanta, Georgia, United States of America.
authors.forename: Miwako
authors.initials: M
authors.lastname: Kobayashi
authors.affiliation: Department of Medicine, Emory University School of Medicine, Atlanta, Georgia, United States of America.
authors.forename: Susan M
authors.initials: SM
authors.lastname: Ray
authors.affiliation: Department of Biostatistics, Emory University Rollins School of Public Health, Atlanta, Georgia, United States of America.
authors.forename: John
authors.initials: J
authors.lastname: Hanfelt
authors.affiliation: Department of Pathology and Laboratory Medicine, Emory University School of Medicine, Atlanta, Georgia, United States of America; Grady Memorial Hospital, Atlanta, Georgia, United States of America.
authors.forename: Yun F
authors.initials: YF
authors.lastname: Wang
mesh_terms: D000293:Adolescent; D000328:Adult; D000368:Aged; D000369:Aged, 80 and over; D018791:CD4 Lymphocyte Count; D003710:Demography; D005260:Female; D015658:HIV Infections / Q000150:complications* / Q000453:epidemiology* / Q000276:immunology; D006801:Humans; D008297:Male; D008875:Middle Aged; D021141:Nucleic Acid Amplification Techniques / Q000379:methods*; D015995:Prevalence; D014376:Tuberculosis / Q000150:complications / Q000175:diagnosis*; D014481:United States / Q000453:epidemiology; D014505:Urban Population / Q000706:statistics & numerical data*; D055815:Young Adult