  In the absence of comprehensive or random testing throughout the COVID-19
pandemic, we have developed a proxy method for synthetic random sampling to
estimate the actual viral incidence in the community, based on viral RNA
testing of asymptomatic patients who present for elective procedures within a
hospital system. The approach collects routine testing data on SARS-CoV-2
exposure among outpatients and performs statistical adjustments of sample
representation using multilevel regression and poststratification (MRP). MRP
adjusts for selection bias and yields stable small area estimates. We have
developed an open-source, user-friendly MRP interface for public implementation
of the statistical workflow. We illustrate the MRP interface with an
application to track community-level COVID-19 viral transmission in the state
of Michigan.
