Trends in disease cases do not imply similar trends in infection prevalence or incidence.

<p>Number of positive exams, total number of exams, infection prevalence, and infection incidence are depicted from upper to lower panels. Left, middle, and right panels are distinct simulations: infection prevalence decreases but the observed number of disease cases increases (left panels), infection prevalence increases but the observed number of disease cases decreases (middle panels), and trends in infection prevalence and incidence do not match the trend in the observed number of disease cases because of concurrent changes in sampling effort (right panels). Multiple simulations with the same initial infection prevalence showed the same qualitative features.