Which statement best defines infection?

Which statement best defines infection?

• A. A microorganism able to overcome the defense barriers and live inside the host
• B. An immune response to a pathogen
• C. A disease caused by vaccination
• D. A symptom of illness

Answer: (A)

Infection is about the microorganism establishing itself inside the host after getting past the body's defenses. It means the microbe has invaded, survived, and possibly multiplied within the host, which can happen with or without causing symptoms. The statement that best captures this is the one describing a microorganism that overcomes the host’s barriers and lives inside the body, since it focuses on the invasion and establishment process essential to infection. The immune response describes how the body reacts, not the event of infection itself; vaccination is about stimulating immunity (not causing disease), and a symptom is a clinical sign of illness, not the act of infection.

Infection is about the microorganism establishing itself inside the host after getting past the body's defenses. It means the microbe has invaded, survived, and possibly multiplied within the host, which can happen with or without causing symptoms. The statement that best captures this is the one describing a microorganism that overcomes the host’s barriers and lives inside the body, since it focuses on the invasion and establishment process essential to infection. The immune response describes how the body reacts, not the event of infection itself; vaccination is about stimulating immunity (not causing disease), and a symptom is a clinical sign of illness, not the act of infection.