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.

Improved sensitivity, safety and laboratory turn around time in the diagnosis of pulmonary tuberculosis by use of bleach sedimentation

Background: Inadequate diagnostic processes and human resources in laboratories contribute to a high burden of tuberculosis (TB) in low- and middle-income countries. Direct smear microscopy is relied on for TB diagnosis; however; sensitivity rates vary. To improve sensitivity of direct microscopy; the researchers employed several approaches; including sputum digestion and concentration of acid-fast bacilli (AFB); a technique which uses commercial bleach. Objectives: This study compared methods used to diagnose active Mycobacterium tuberculosis infections. Methods: Three sputum specimens were collected from each of 340 participants in Abuja; Nigeria; over two consecutive days. Direct microscopy was performed on all specimens; following microscopy; one specimen from each patient was selected randomly for bleach sedimentation and one for Lowenstein-Jensen culture.Results: Direct microscopy produced 28.8% AFB-positive results; whilst bleach sedimentation resulted in 30.3%. When compared with the cultures; 26.5% were AFB true positive using direct microscopy and 27.1% using bleach sedimentation. Whilst the specificity rate between these two methods was not statistically significant (P = 0.548); the sensitivity rate was significant (P = 0.004).Conclusion: Based on these results; bleach increases the sensitivity of microscopy compared with direct smear and has similar specificity. When diagnosing new cases of pulmonary TB; one bleach-digested smear is as sensitive as three direct smears; reducing waiting times for patients and ensuring the safety of laboratory technicians

Evaluation of Commercial Rapid Diagnostic Test Kit for Tuberculosis: Further Evidence Supporting Negative Policy on the Use of Serological Tests for Pulmonary Tuberculosis Diagnosis in Developing Countries.

Aim: To know whether one of the commercially available immunochromatographic tuberculosis tests is comparable with the widely available method, direct sputum microscopy. Design: The study prospectively validated the pulmonary tuberculosis rapid test kit using the reference standard, Lowenstein Jensen culture and compared the outcome with the direct sputum microscopy. Place and Duration: The study was conducted in Zankli Medical Centre, Abuja, between November 2004 and July 2005. Methodology: 340 patients 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 microscopy and culture were performed on these samples. Also, 4ml of blood were collected from the same patients for antibody detection using immunochromatographic technique. Results: The evaluated rapid diagnostic kit when compared with the reference standard has a sensitivity of 59.3% and 81.1% specificity. Sensitivity and specificity of direct microscopy, when compared with the rapid test is statistically significant (P=0.001); indicating diagnostic accuracy of the conventional method of pulmonary tuberculosis testing over the immunochromatographic test. Conclusions: The conventional test indicated high performance in this report and it is suggestive of the relevance and diagnostic accuracy of the widely available method in the diagnosis of pulmonary tuberculosis in developing countries. This assertion is also, supported by the 2008 WHO/TDR report on evaluation of nineteen tuberculosis rapid diagnostic kits.