Which statement best describes an infectious disease?

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

Answer: (B)

The main idea is that an infectious disease is caused by a microbial agent that can move from one person to another. This means the illness comes from a microbe—like a virus, bacteria, fungus, or parasite—and the same agent can be transmitted between people through contact or other transmission routes. That transmission between hosts is the hallmark of infectiousness, which is precisely what the statement describes: a microbial contaminant capable of spreading from host to host through contact.

In contrast, a chemical contaminant causes illness through toxins rather than infection by a pathogen, a genetic mutation leads to disease through altered host biology without involving a transmissible microbe, and a non-infectious disease is not caused by a spreading microbial agent.