Feasibility of controlling COVID-19 outbreaks by isolation of cases and contacts

Hellewell, Joel; Abbott, Sam; Gimma, Amy; Bosse, Nikos I; Jarvis, Christopher I; Russell, Timothy W; Munday, James D; Kucharski, Adam J; Edmunds, W John; Funk, Sebastian; Eggo, Rosalind M

In many scenarios, between 25 and 100 symptomatic cases occurred in a week at the peak of the simulated outbreak ( figure 5 ). All of these cases, and their contacts, would need to be isolated. Large numbers of new cases can overwhelm isolation facilities, and the more contacts that need to be traced, the greater the logistical task of following them up. In the 2014 Ebola epidemic in Liberia, each case reported between six and 20 contacts, 8 and the number of contacts seen in MERS outbreaks is often higher than that. 10 20 contacts for each of 100 cases means 2000 contacts traced to achieve control. Uncontrolled outbreaks typically had higher numbers of cases (appendix p 13). The maximum numbers of weekly cases Figure 5 : The maximum weekly cases requiring contact tracing and isolation in scenarios with 20 index cases that achieved control within 3 months Scenarios vary by reproduction number and the mean delay from onset to isolation. 15% of transmission occurred before symptom onset, and 0% subclinical infection. The percentage of simulations that achieved control is shown in the boxplot. This illustrates the potential size of the eventually controlled simulated outbreaks, which would need to be managed through contact tracing and isolation. *The interval extends out of the plotting region. figure 5 might appear counterintuitive, because a lower maximum number of weekly cases is not associated with higher outbreak control. This occurs because with better contact tracing it becomes possible to control outbreaks with higher numbers of weekly cases.