For sputum smear to come positive on ZN staining there should be minimum:-
100 bacilli per per ml sputum
1000 bacilli per ml sputum
2000 bacilli per ml sputum
10,000 bacilli per ml sputum
Sputum smear microscopy for tubercle bacilli is positive when there are at least 10,000 organisms present per ml of sputum. ZN staining in RNTCP: Acid fast bacilli of TB; 'Rod shaped' with 'beaded appearance'. >10,000 bacilli per ml sputum must be present for a positive result.
RNTCP