Lessons learnt from 288 COVID-19 international cases: importations over time, effect of interventions, underdetection of imported cases

Francesco Pinotti; Laura Di Domenico; Ernesto Ortega; Marco Mancastroppa; Giulia Pullano; Eugenio Valdano; Pierre-Yves Boelle; Chiara Poletto; Vittoria Colizza

Underdetection may be due to several different factors including asymptomatic infections, infections with mild clinical symptoms, health-seeking behavior and declaration of travel history, case definition, and underdiagnosis. Underdetection of imported cases is likely to be higher than what we estimate here, as our analysis is conditional to the identification of clusters of cases. The current situation in Italy, with different clusters emerging in the timeframe of few hours in different areas in the North of the country 14 , shows that clusters have gone undetected and epidemiological links with the index case are still missing. Countries outside China should be prepared for the possible emergence of several undetected clusters of chains of local transmissions. Surveillance efforts to track all suspect cases may become impractical if the number of cases increases too rapidly 32 . If that situation occurs, countries should be ready to step-up their response and take preparatory steps for community interventions.