What are the three corners of the epidemiologic triad?

• A. Viral, Bacterial, Fungal
• B. Genetics, behavior, immunity
• C. Population, exposure, susceptibility
• D. Agent/pathogen factors, host factors and environmental factors

Answer: (D)

The idea being tested is that disease results from the interaction of three elements: the agent, the host, and the environment. The correct answer names exactly these three corners: agent/pathogen factors, host factors, and environmental factors. Each element plays a role in whether disease occurs. The agent contributes characteristics like virulence and infectivity; the host contributes susceptibility and immune status; the environment provides conditions that affect exposure and transmission, such as crowding, sanitation, or climate. For example, influenza spread is shaped by the virus itself, people’s immunity, and crowded indoor settings in winter. The other options don’t capture the full three-way interaction: one focuses only on pathogen types; another combines host traits but omits environment; and another lists epidemiologic terms rather than the three corner factors of the triad.