Optimal COVID-19 quarantine and testing strategies

Wells, Chad R.; Townsend, Jeffrey P.; Pandey, Abhishek; Krieger, Gary; Singer, Burton; McDonald, Robert H.; Moghadas, Seyed M.; Galvani, Alison P.

As economic woes of the COVID-19 pandemic deepen, strategies are being formulated to avoid the need for prolonged stay-at-home orders, while implementing risk-based quarantine, testing, contact tracing and surveillance protocols. Given limited resources and the significant economic, public health and operational challenges of the current 14-day quarantine recommendation, it is vital to understand if more efficient but equally effective quarantine and testing strategies can be deployed. To this end, we developed a mathematical model to quantify the probability of post-quarantine transmission that varied across a range of possible quarantine durations, timings of molecular testing, and entry uniformly across infection time course or entry as a traced contact. Assuming cases entering quarantine uniformly across infection time course and a one-day delay for testing and, we found that a 13-day quarantine with testing on entry, a seven-day quarantine with testing on exit, and a seven-day quarantine with testing on both entry and exit each provide equivalent or lower probability of post-quarantine transmission compared to a 14-day quarantine with no testing. We found that testing on exit from quarantine is more effective in reducing probability of post-quarantine transmission than testing upon entry. When conducting a single test, testing on exit was most effective for quarantines lasting up to six days. For longer quarantines, the optimal test day was day five or day six. These results differed by no more than one day for cases entering quarantine as traced contacts. Optimal timing of testing during quarantine will reduce the probability of post-quarantine transmission, as false-positive results become less likely, enabling case isolation. Based on 4,040 SARS CoV-2 RT-PCR tests, an exit test 96 hours after the start of quarantine for an offshore oil rig population was demonstrated to identify all known asymptomatic cases that previously tested negative at entry, and—moreover—successfully prevented an expected nine offshore transmission events, each a serious concern for initiating rapid spread and a disabling outbreak in the close quarters of an offshore rig. This successful outcome highlights the importance of context-specific guidelines for the duration of quarantine and timing of testing that can minimize economic impacts, disruptions to operational integrity, and COVID-related public health risks.