Case-Detection Rate of Direct Sputum Smear Microscopy for Diagnosis of Pulmonary Tuberculosis in Abia State, Nigeria

Abstract

The accuracy of sputum smear microscopy, the tuberculosis case-finding method in the Abia State TB Control Programme has never been assessed due to lack of culture facilities. To assess the accuracy of sputum smear microscopy in routine control programme conditions in Abia State, sputum samples from patients undergoing investigation for tuberculosis were analyzed using Ziehl-Neelsen staining technique for sputum smear microscopy and culture on Lowenstein-Jensen medium as reference standard. Out of 150 participants tested, 51 were smear –positive for acid fast bacilli (positivity rate, 34.0 %, 51/150) while 79 were culture positive for Mycobacterium tuberculosis complex and 12 for non-tuberculous mycobacteria (NTM). Thirty-seven of the 79 culture positive for M. tuberculosis were smear positive giving a ratio of smear to culture positivity of 46.84%. Forty-two (42.4%) of the 99 smear negative cases were culture positive for M. tuberculosis. The sensitivity of smear microscopy was 50.0% (95%CI=39.0-61.0) and specificity was 92.3% (95% CI=86.4-98.2). The prevalence of HIV/TB coinfection among the study participants was 48% (12/25). Although the case- detection rate of smear microscopy was moderate in this study, the large proportion of TB patients missed by smear microscopy is a cause for concern and requires concerted effort to improve the sensitivity of smear microscopy. Introduction of more sensitive diagnostic methods like culture also need to be considered. La precision des frottis, la methode la recherche de cas de tuberculose dans le programme de lutte contre la tuberculose dans l’Etat d'Abia n'a jamais ete evalue en raison du manque d'installations de culture. Pour evaluer la precision des frottis dans les conditions du programme de controle de routine dans cet Etat , les expectorations de patients subissant une enquete de la tuberculose ont ete analysees a l'aide de technique de coloration de Ziehl-Neelsen pour la microscopie des frottis de crachats et de la culture sur milieu de Lowenstein- Jensen en tant que norme de reference . Sur les 150 participants testes, 51 etaient a frottis positif pour les bacilles acido rapide (taux de positivite, 34,0%, 51/150), tandis que 79 etaient positifs a la culture pour complexe Mycobacterium tuberculosis et 12 pour les mycobacteries non tuberculeuses (NTM). Trente-sept de la culture 79 positive pour M.tuberculosis etaient a frottis positif donnant un ratio de frottis de positivite de la culture de 46,84 %. Quarante-deux (42,4%) des 99 cas a frottis negatifs etaient positifs a la culture pour M. tuberculosis. La sensibilite de la microscopie des frottis etait de 50,0 % (IC a 95% = 39,0 a 61,0) et la specificite etait de 92,3 % (IC a 95% = 86,4 a 98,2). La prevalence du VIH / TB coinfection parmi les participants a l'etude etait de 48% (12 /25). Bien que le taux de microscopique des frottis de depistage des cas ait ete modere dans cette etude, la forte proportion de patients atteints de tuberculose manques par examen microscopique des frottis est un sujet preoccupant et exige un effort concerte pour ameliorer la sensibilite de la microscopie des frottis. La presentation des methodes de diagnostic plus sensibles comme la culture doivent aussi etre pris en consideration.