The infectiousness of tuberculosis (TB) is directly related to the number of Mycobacterium tuberculosis organisms expelled into the air by an infected patient.

Step-by-Step Justification:

TB Transmission Mechanism:

TB spreads through airborne droplet nuclei, which remain suspended for long periods​.

Factors Affecting Infectiousness:

High bacterial load in sputum: Smear-positive patients are much more infectious​.

Coughing and sneezing frequency: More expelled droplets increase exposure risk.

Environmental factors: Poor ventilation increases transmission​.

Why Other Options Are Incorrect:

A. Hand hygiene habits: TB is airborne, not transmitted via hands.

B. Presence of acid-fast bacilli (AFB) in blood: TB is not typically hematogenous, and blood AFB does not correlate with infectiousness.

C. Tuberculin skin test (TST) >20 mm: TST indicates prior exposure, not infectiousness.

CBIC Infection Control References:

APIC Text, "Tuberculosis Transmission and Control Measures"​.