In the chain of infection, which would be considered an infectious agent?

• A. Human host
• B. Excessive heat
• C. Overcrowding
• D. Tuberculosis

Answer: (D)

Infectious agent is the microorganism that can cause disease. Tuberculosis is caused by Mycobacterium tuberculosis, a bacterium that invades the respiratory tract and can multiply to produce illness. This organism is the actual infectious agent responsible for initiating infection, fitting the definition in the chain of infection.

The human host is the person who can become ill after exposure; they are the recipient, not the organism itself. Excessive heat is an environmental condition that can influence the survival of some pathogens, but it is not the infectious agent. Overcrowding is a social/environmental factor that can facilitate transmission, again not the organism responsible for disease.