A Statistical Definition of Epidemic Waves

The timely identification of expected surges of cases during infectious disease epidemics is essential for allocating resources and preparing interventions. This study describes a simple way to evaluate whether an epidemic wave is likely to be present based on daily new case count data. The proposed measure compares two models that assume exponential or linear dynamics, respectively. Technically, the output of two regression analyses is used to approximate a Bayes factor, which quantifies the support for the exponential over the linear model and can be used for epidemic wave detection. The trajectory of the coronavirus epidemic in three countries is analyzed and discussed for illustration. The proposed measure detects epidemic waves at an early stage, which are otherwise visible only by inspecting the development of case count data retrospectively. In addition to informing public health decision making, the outlined approach may serve as a starting point for scientific discussions on epidemic waves.