A comparative evaluation of acid fast bacilli positivity by slit skin smears, bacterial index of granuloma in paucibacillary and multibacillary leprosy types as per WHO operational classification

The diagnosis and classification of leprosy still remains a challenge. Less than desired specificity and sensitivity of operational WHO classification may result in administering inadequate/ over treatment in some cases. The aim of this study was to analyse Paucibacillary (PB) and Multibacillary (MB) classified by WHO operational criteria for positivity for acid fast bacilli (AFB) by Slit Skin Smears (SSS) and Bacterial Index of Granuloma (BIG) in the tissue sections from these leprosy cases using Job-Chacko modification of Fite Faraco (FF) staining and modified Ziehl Neelsen (ZN) staining. In case of 30 cases classified as PB by clinical criteria, AFB could be detected in 2/30 (6.6%) by SSS, 5/30 (16.7%) by BIG - modified ZN and 8/30 (26.67%) by BIF-FF. On the other in clinically MB patients, AFB positivity was 42/70 (60%) by SSS, 56/70 (80%) by BIG-modified ZN and 63 (90%) by BIG-FF. Clinical relevance of these findings needs to be determined by therapeutic outcomes of present regimens being used for these PB/MB types. The Inter-rater agreement (kappa) is 0.64. BIG by ZN stain showed no bacilli in 39 patients among which 10 patients showed bacilli in histopathology stained by FF stain. It may be worthwhile to consider adding estimation of BIG in the diagnostic work up of Paucibacillary (PB) cases classified by WHO clinical criteria and study its implications in terms of therapeutic outcomes. If found useful therapeutically, such services can be made available in Tertiary Care Institutions.