In 4 split skin smears of a patient, 2 samples had 10 bacilli out of 100hpf and 2 samples with > 1000 bacilli. Average bacteriological index would be

RIDLEY'S LOGARITHMIC SCALE FOR BACTERIAL INDEX Bacterial/ Bacteriological Index (BI) : Density of bacilli in smears, including both living and dead bacilli. Ridley's logarithmic scale : Based on the number of bacilli seen in an average High power microscopic field, using an oil-immersion objective (1/12 in or 2 mm) When several smears are taken: Mean index is calculated. Score Description 6+ Many clumps of bacilli in an average field (over 1000) 5+ 100-1000 bacilli in an average field 4+ 10-100 bacilli in an average field 3+ 10-100 bacilli in 10 fields 2+ 1-10 bacilli in 10 fields 1+ 1-10 bacilli in 100 fields In the given question, Two samples have 10 bacilli in 100hpf (each1+score), and Tw samples with >1000 bacilli in Average filed (each 6+ score) BI = 1+1+6+6/ 4 = 3.5 Ref: Park 25th edition Pgno : 341-342