Which of the following is NOT one of the three primary modes of disease transmission used in infection control?

• A. Contact transmission
• B. Droplet transmission
• C. Airborne transmission
• D. Vector-borne transmission

Answer: (D)

Infection control classically groups disease spread into three main routes: direct or indirect contact with an infected person or contaminated surfaces (hand hygiene and gloves prevent this), droplets from the mouth or nose that travel short distances and reach mucous membranes (masks and eye protection help here), and small airborne particles that can linger in the air and travel longer distances (requiring N95 respirators and specialized rooms). Vector-borne transmission, on the other hand, involves pathogens delivered by a living carrier such as a mosquito or tick. That mechanism is separate from the three primary routes and isn’t counted among them in standard infection-control frameworks. Because the question asks which is not one of the three primary modes, vector-borne transmission is the correct choice.