title: Value of dual testing for identifying tuberculous infection.
abstract: METHODS
  A rural community in Chingleput district in Tamil Nadu state in south India.
  
  
  OBJECTIVE
  To determine the value of dual testing with PPD-S and PPD-B for identifying subjects with a tuberculous infection.
  
  
  METHODS
  About 240,000 subjects in rural south India, all of whom were tested initially with PPD-S and PPD-B, were followed up for 15 years, mainly by total population survey once in every 212 years. The incidence of culture-positive tuberculosis was estimated using life-table technique.
  
  
  RESULTS
  Among 17,530 subjects with an intermediate reaction (8-11 mm) to PPD-S at intake, 285 with an induration to PPD-S exceeding the induration to PPD-B by at least 2mm, had a significantly higher incidence of culture-positive tuberculosis than the remaining (154 and 93 per 100,000), and similarly 481 who had an induration of <10mm to PPD-B compared to those with >or=10 mm (131 and 93 per 100,000). These subjects may be regarded as having a tuberculous infection. Infection with non-tuberculous mycobacteria conferred protection of about 30% against the development of tuberculosis over a 15-year period.
  
  
  CONCLUSIONS
  In subjects with an intermediate reaction (8-11 mm) to PPD-S, dual testing with PPD-B enabled identification of those with a tuberculous infection. Most of the reactions were due to non-tuberculous mycobacteria.
authors.affiliation: Tuberculosis Research Centre (ICMR), Mayor V.R. Ramanathan Road, Chetput, Chennai 600 031, India.
authors.forename: S
authors.initials: S
authors.lastname: Radhakrishna
authors.forename: T R
authors.initials: TR
authors.lastname: Frieden
authors.forename: R
authors.initials: R
authors.lastname: Subramani
authors.forename: P R
authors.initials: PR
authors.lastname: Narayanan
mesh_terms: D000293:Adolescent; D000328:Adult; D002648:Child; D002675:Child, Preschool; D005260:Female; D005500:Follow-Up Studies; D006306:Health Surveys; D006801:Humans; D015994:Incidence; D007194:India / Q000453:epidemiology; D007223:Infant; D007231:Infant, Newborn; D008297:Male; D008875:Middle Aged; D015999:Multivariate Analysis; D009169:Mycobacterium tuberculosis / Q000302:isolation & purification*; D014373:Tuberculin / Q000627:therapeutic use; D014374:Tuberculin Test / Q000379:methods; D014376:Tuberculosis / Q000175:diagnosis* / Q000453:epidemiology
chemical_list: D014373:Tuberculin