When trying to determine whether the swine flu outbreak was getting worse, which rate should be carefully observed?

Correct Answer: C

Rationale: The incidence rate of new cases would be most useful for detecting short-term acute disease changes, because the swine flu duration is usually relatively short. The prevalence rate is the number of all cases of a specific disease or condition in a population at a given point in time. Crude death rates summarize the occurrence of mortality. An age-specific death rate characterizes the death rates of a particular age group in the population.

Correct Answer: B

Rationale: Prevalence = Incidence × Duration. If survival time with the disease increases (B), duration rises, increasing prevalence (e.g., better treatment for HIV increases the number living with it). A decreases incidence, lowering prevalence. C shortens duration via faster recovery, reducing prevalence. D increases the population size but not prevalence (proportion) if incidence and duration are constant.

Correct Answer: B

Rationale: A pandemic (B) is a widespread outbreak across multiple countries or continents (e.g., COVID-19). A is an epidemic, C is localized, and D is seasonal (e.g., flu), not necessarily pandemic.

Correct Answer: C

Rationale: The triad is host (A), agent (B), and environment (D). Vector (C) is a transmission mode, not a core component.

Correct Answer: B

Rationale: Prevalence (B) is total cases at a time (e.g., diabetes prevalence). A is incidence, C is mortality, D is at-risk population.