Certified in Public Health (CPH) Practice Exam

What does the typical 'bell curve' of new influenza case incidence represent?

1. The combined operation of two feedback loops in which the positive feedback loop dominates early and the negative feedback loop dominates later

2. The isolated operation of a positive feedback loop

3. The combined operation of two constant and equally influential feedback loops

4. The isolated operation of a negative feedback loop

The correct answer is: The combined operation of two feedback loops in which the positive feedback loop dominates early and the negative feedback loop dominates later

The typical 'bell curve' of new influenza case incidence represents a dynamic interplay between positive and negative feedback loops in the progression of an outbreak. At the beginning of an influenza season, there is a rapid increase in cases due to the positive feedback loop, where rising case numbers lead to increased transmission. This phase is characterized by a surge in infections, as more individuals contracting the virus creates opportunities for further spread. As the outbreak progresses, various factors come into play that begin to invoke a negative feedback loop. This might include the implementation of public health interventions, increased immunity in the population, or the natural course of disease dynamics where fewer susceptible individuals remain. This shift leads to a decline in new case incidence, resulting in the characteristic peak and subsequent tapering off of the bell curve. Thus, the typical bell curve represents the transition from an initial rapid increase (positive feedback) to a stabilization and decrease in cases (negative feedback). This understanding emphasizes the importance of both feedback mechanisms in shaping the epidemiological patterns of infectious diseases like influenza.