Table 2.

Scenarios that can lead to changes in the ratio of log transformed case to wastewater data.

Ratio	Changes to factors contributing to case data	Changes to factors contributing to wastewater signal	Both
Increase	Increased diagnostic testing rates without proportional increase in incidence	Increase in incidence that is captured in the case data but is not reflected in wastewater data due to lower shedding rate or duration	Tested cases increase before this is reflected in the wastewater data Tested cases increase more steeply than is reflected in the wastewater data
Decrease	Increase in incidence reflected in wastewater data is not reported in case data due to undertesting	Higher wastewater values due to increased shedding rate or duration	Wastewater values increase before cases reflect the change (undertesting)