Value of dual testing for identifying tuberculous infection.
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.
Radhakrishna
S
S
Tuberculosis Research Centre (ICMR), Mayor V.R. Ramanathan Road, Chetput, Chennai 600 031, India.
Frieden
T R
TR
Subramani
R
R
Narayanan
P R
PR
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
D014373:Tuberculin