Modeling the Comparative Impact of Individual Quarantine vs. Active Monitoring of Contacts for the Mitigation of COVID-19

Corey M Peak; Rebecca Kahn; Yonatan H Grad; Lauren M Childs; Ruoran Li; Marc Lipsitch; Caroline O Buckee

Interventions based on contact tracing, unlike mass interventions such as travel restrictions and social distancing, are targeted at individuals and therefore require resources --material and personnel --proportional to the number of cases traced: contact tracing requires detailed interview of case patients to learn of contacts and public health outreach to trace them; active monitoring of contacts may include twice-daily visits by healthcare workers or phone-based self-monitoring; 14 and individual quarantine of contacts requires private space, provision of essentials, and investment in enforcement. The burden of implementing active monitoring or individual quarantine grows quickly as a function of disease incidence and the fraction of traced contacts who are not infected. Assuming uninfected contacts (who never develop symptoms) are monitored or quarantined for 14 days before clearance, the number of uninfected contacts followed grows more quickly than truly infected contacts ( Figure 1 ). As the ratio of uninfected:infected contacts traced increases from 1:1 to 9:1, for example, the burden of uninfected contacts grows proportionally; note the actual ratio may be closer to 2,318:1, as recorded during SARS control in Taiwan where 24 (0.04%) of 55,632 quarantined contacts were found to be truly infected. 15 Depending on the ratio of uninfected to infected contacts traced, individual quarantine, even if initially effective, may soon become infeasible as the epidemic grows, and will need to be supplemented or deprioritized to focus resources on other interventions such as social distancing.