Which description best defines infectious disease?

• A. A genetic disorder
• B. A non-infectious disease
• C. A microbial contaminant that can spread from host to host through contact
• D. A lifestyle factor

Answer: (C)

Infectious disease is caused by pathogens—microbes such as bacteria, viruses, fungi, or parasites—that have the ability to move from one person to another. The essential feature is transmission between hosts, through routes like direct contact, droplets, airborne spread, contaminated surfaces, or vectors. This description fits best because it links the illness to a microbe and to its capacity to spread from one person to another.

Genetic disorders are inherited conditions not caused by microbes. Non-infectious diseases are illnesses that aren’t transmitted between people. Lifestyle factors are behaviors or exposures that can influence risk but are not diseases themselves.