Travel-associated COVID-19: a challenge for surveillance?

The coronavirus disease (COVID-19) pandemic started in late 2019 in Wuhan, China before spreading globally in the following months, first in Asia and Europe, followed by the Americas, Africa and Oceania [1]. The substantial morbidity and mortality associated with the pandemic led countries to implement exceptional public health measures, including stay-at-home recommendations and orders. In many countries, observed epidemiological patterns were similar and initially imported cases were soon followed by community transmission [2,3]. In countries that managed to control the local epidemics, reporting of cases continued at lower levels, with a large proportion of imported cases in some [4]. In Europe, the proportion of imported cases increased in June and July 2020 compared with previous months, probably driven by testing that targeted travellers as travel restrictions were eased [5]. Cases reported as imported encompass a variety of situations that may challenge surveillance indicators.