Background: The emergence in China in late 2019 and subsequent progression of a pandemic of a respiratory disease named coronavirus disease 2019 (COVID-19) was highly facilitated by international travel . We present 5 cases of probable in-flight transmission in Greece .
Methods: We studied international passengers arriving to or departing from Greece from February 26 through March 9 , 2020 . Contact tracing extended up to 4 days before the onset of symptoms and focused on close contacts . Close contacts were defined as persons sitting within a distance of <2 meters for> 15 minutes, including passengers seated two seats around the index case and all crew members and persons who had close contact with the index case .
Results: We investigated 18 international flights with 2224 passengers and 110 crew members . Main countries of departure included Northern Italy, Israel and the United Kingdom . In accordance with the national surveillance investigation, in these flights there were 21 index cases and 891 contact traced cases . Six index cases were symptomatic during the flight . Of the 891 contact traced cases , 4 passengers and 1 crew member developed laboratory-confirmed infection (3 with COVID-19 and 2 with asymptomatic infection); they travelled on the same flight with two COVID-19 cases .
Conclusions: Air travel has played a central role in the progression of the COVID-19 pandemic . However, there are scarce data about in-flight transmission . Our extensive investigation showed five cases of probable in-flight transmission . Efforts should be placed in order to ensure the prompt implementation of appropriate infection control measures on board.