Quantifying bias of COVID-19 prevalence and severity estimates in Wuhan, China that depend on reported cases in international travelers

Rene Niehus; Pablo M De Salazar; Aimee Taylor; Marc Lipsitch

We previously showed that there was variability between locations in the world in the relationship between the number of travelers from Wuhan to each international destination and the number of imported cases detected in that destination. On average, for countries presumed to have high surveillance capacity, one imported case reported over the period 8th January to 4th February was associated with each additional 14 passengers/day historical travel volume 5 . However there was variation around this average. Among countries with substantial travel volume, Singapore showed the highest ratio of detected imported cases to daily travel volume, a ratio of one case per 5 daily travelers. Singapore is historically known for exceptionally sensitive detection of cases, for example in SARS 6 , and has had extremely detailed case reporting during the COVID-19 outbreak 7 . We therefore use Singapore in this work as the upper limit of case detection capacity. And we estimate this capacity of other locations relative to Singapore.