Gastric aspirate smear microscopy as a diagnostic tool for childhood pulmonary tuberculosis

Abstract

Background: Most tuberculosis (TB) control programs use positive sputum Ziehl-Neelsen (Z-N) smear microscopy results as a basis for TB case confirmation, valid enough to warrant commencement of treatment. Children do not only produce poor quality sputum a proportion cannot produce sputum, at all. Gastric aspirate (GA) smear microscopy, a recommended alternative, is the only available bacteriologic test in most health-care institutions. Objectives: This study was aimed to determine the usefulness of acid fast smears of GA for the diagnosis of pulmonary TB in children. Materials and Methods: A total of 263 GA samples from children with suspected pulmonary TB underwent Z-N staining and culture on Ogawa medium. Acid-fast isolates on Ogawa medium were sub-cultured on Ogawa medium containing para-nitrobenzoic acid (PNBA-Ogawa medium). Lack of growth on PNBA-Ogawa confirmed Mycobacterium tuberculosis complex (MTBC) and ruled out non-tuberculous mycobacteria. Validity parameters were calculated with GA culture as Gold standard. Results: GA samples from 33 (12.5%) of the 263 patients were smearing positive. However, GA culture on Ogawa medium was positive for MTBC in 97 (37%) of the 263 patients. Twenty-nine of the 97 culture-positive GA were also Z-N smear-positive, giving a GA Z-N smear sensitivity of 29.9%. Of the166 culture-negative cases, 162 were Z-N smear-negative, giving a GA Z-N smear specificity of 97.6%. Positive- and negative-predictive values were 88% and 70% respectively. Conclusion: GA smear microscopy is highly specific for diagnosis of pulmonary TB in children. The test can be useful in culture facility-limited settings as acceptable sensitivity can be achieved if specimen collection/handling protocols are strictly adhered to.