Predictive value of the acid fast smear for detection of Mycobacterium tuberculosis in respiratory specimens in a reference center of HIV/Aids in Riode Janeiro, Brazil

In order to evaluate the predictive value of acid fast bacilli (AFB) smear for the diagnosis of Mycobacterium tuberculosis in respiratory specimens in a setting with a high prevalence of Aids and art unknown prevalence of non tuberculous mycobacteria (NTM), we retrospectively examined specimens cultu red for mycobacteria between I September 1993 and 30 September 1994 and med ical records of patients with positive culture in a General Hospital, Aids reference in Rio de Janeiro, Brazil. Seventy three ps cent (1517/2077) of s amples were respiratory specimens and mycobacteria were recovered from 20.6 % (313/1517) of these. M. tuberculosis was identified in 94.2% (295/313) an d NTM in 5.8% (18/313). The yield of positive AFB smear and of positive cul ture was 6.1% (93/1517) and 20.6% (313/1517), respectively. The positive pr edictive value (PPV) of AFB for M. tuberculosis was 98.4% in expectorated s putum and 96.4% in bronchoalveolar lavage. Forty four percent (130/295) of specimens with positive culture for M. tuberculosis and 66.7% (12/18) for N TM were from patients HIV positive. The conclusion was that in our study po pulation, the PPV of AFB for M. tuberculosis in respiratory specimens was h igh and the prevalence of NTM was low despite the high prevalence of HIV po sitive.