Which statement best explains how infectious diseases are different from any other health problem?

Correct Answer: D

Rationale: Because of their potential to spread and cause communitywide or worldwide emergencies, infectious diseases require organized, public efforts for their prevention and control. Most human diseases (e.g., cancer or diabetes) can be classified as personal health problems. Individuals with a personal health problem can be treated by the health care system one person at a time. By contrast, infectious diseases are categorized as public or community health problems.

Correct Answer: A

Rationale: By definition, a cross-sectional study examines relationships between potential causal factors and disease at a specific time. A prospective study monitors a group of disease-free individuals to determine if and when disease occurs. A retrospective study compares individuals with a particular condition or disease with those who do not have the disease. A true experiment involves both an experimental group who receives an intervention and a control group who does not receive an intervention.

Correct Answer: B

Rationale: In epidemiology, the 'population at risk' is the group susceptible to the outcome of interest (e.g., those who could develop lung cancer in a smoking study). Choice B correctly defines this as those who may experience the outcome. A focuses on behavior, not susceptibility. C implies harm from the study itself, not the outcome. D refers to relative risk, a measure, not the group definition.

Correct Answer: A

Rationale: Endemic (A) describes a disease consistently present at a stable level in a population (e.g., malaria in some regions). B is an epidemic, C an emerging disease, and D eradication.

Correct Answer: B

Rationale: Case fatality rate (B) measures severity as deaths among cases (e.g., Ebola). A is new cases, C is total cases, D is deaths broadly.