Repeat SARS-CoV-2 Testing Models for Residential College Populations

Chang, J. T.; Crawford, F. W.; Kaplan, E. H.

Residential colleges are considering re-opening under uncertain futures regarding the COVID-19 pandemic. We consider repeat SARS-CoV-2 testing models for the purpose of containing outbreaks in the residential campus community. The goal of repeat testing is to rapidly detect and isolate new infections as they occur to block transmission that would otherwise occur on campus and, of arguably greater importance, off. The models allow for the evolution of test sensitivity with time from infection, scheduled on-campus resident screening at a given frequency, imported infections from off campus throughout the school year, and a lag from testing until student isolation due to laboratory turnaround and student relocation delay. For early- (late-) transmission of SARS-CoV-2 by age of infection, we find that weekly screening cannot reliably contain outbreaks with reproductive numbers above 1.4 (1.6) if more than one imported exposure per 10,000 students occurs daily. Screening every three days can contain outbreaks providing the reproductive number remains below 1.75 (2.3) if transmission happens earlier (later) with time from infection, but at the cost of greatly increased false positive rates requiring more isolation quarters for students testing positive. Testing frequently while minimizing the delay from testing until isolation for those found positive are the most controllable levers for preventing large residential college outbreaks.