Which of the following best defines epidemiology in the context of public health?

Which statement most accurately summarizes the primary roles of the CDC and WHO?

During a 6-month surveillance period in a town of 50,000 people, 200 people developed a novel infection. At the start of the period, 400 individuals were known to already have the infection and are not at risk. What is the incidence proportion over the 6 months (expressed as a percentage)?

On a single day snapshot, a city of 200,000 residents reports 1,000 people currently infected with disease X, including 100 new diagnoses that week and 900 preexisting cases. What is the point prevalence proportion (%) on that day?

A chronic disease has low incidence (new cases few per year) but high prevalence because people live many years with the condition. Describe how incidence, prevalence, and average disease duration are mathematically related and explain why prevalence remains high despite low incidence.