Effectiveness of Tuberculosis Smear Microscopy in Laboratory Diagnosis of Mycobacterium tuberculosis in Resource Constrained Settings

Aim: To determine the correlation of accuracy of direct smear microscopy compared with BACTEC MGIT 960.

Design: The study prospectively compare direct smear microscopy with BACTEC MGIT 960 using the reference standard, Lowenstein Jensen culture.

Place and Duration: The study was conducted in Zankli Medical Centre, Abuja, between November 2004 and July 2005.

Methodology: 340 suspected patients for Mycobacterium tuberculosis referred from direct observation therapy clinics located in six different government owned health facilities were referred to our facility. These patients; male (192) and female (148) were between the age of 10 and 64 years old. Three sputa samples were collected over two consecutive days and direct smear microscopy and culture were performed on these samples.

Results: When compared with the reference standard, BACTEC MGIT 960 has a sensitivity and specificity of 100.0% and 56.4% respectively, and a negative predictive value of 100.0%; indicating the proportion of AFB negative participants were actually not infected with M. tuberculosis when tested with BACTEC MGIT 960. The sensitivity of direct microscopy was significantly lower than BACTEC MGIT 960 (84.9% versus 100%, p<0.001) and the specificity was significantly higher (96.6% versus 56.4%, p<0.001).

Conclusions: For the purpose of effectiveness of tuberculosis program in developing countries, direct smear microscopy may still be relevant in the diagnosis of Mycobacterium tuberculosis.