Asymptomatic Transmission of SARS-CoV-2 on Evacuation Flight

Sung Hwan Bae; Heidi Shin; Ho-Young Koo; Seung Won Lee; Jee Myung Yang; Dong Keon Yon


Emerging Infectious Diseases. 2020;26(11):2705-2708. 

In This Article

The Study

On March 31, 2020, we enrolled in our study 310 passengers who boarded an evacuation flight from Milan, Italy, to South Korea. This evacuation flight was conducted under strict infection control procedures by the Korea Centers for Disease Control and Prevention (KCDC), based on the guidelines of the World Health Organization (WHO).[4] When the passengers arrived at the Milan airport, medical staff performed physical examinations, medical interviews, and body temperature checks outside the airport before boarding, and 11 symptomatic passengers were removed from the flight. Medical staff dispatched from KCDC were trained in infection control under the guidance of the KCDC and complied with the COVID-19 infection protocol, which was based on WHO guidelines.[4] N95 respirators were provided, and passengers were kept 2 m apart for physical distancing during preboarding. Most passengers wore the N95 respirators except at mealtimes and when using the toilet during the flight. After an 11-hour flight, 299 asymptomatic passengers arrived in South Korea and were immediately quarantined for 2 weeks at a government quarantine facility in which the passengers were completely isolated from one another. Medical staff examined them twice daily for elevated body temperature and symptoms of COVID-19. All passengers were tested for SARS-CoV-2 by reverse transcription PCR twice, on quarantine day 1 (April 2) and quarantine day 14 (April 15).

Asymptomatic patients were those who were asymptomatic when they tested positive and did not develop symptoms within 14 days after testing.[5] Among the 299 passengers (median age 30.0 years; 44.1% male), 6 had a confirmed positive result for SARS-CoV-2 on quarantine day 1 and were transferred immediately to the hospital (Table). At 14 days after the positive test, the 6 patients reported no symptoms and were categorized as asymptomatic

On quarantine day 14, a 28-year-old woman who had no underlying disease had a confirmed positive test result for COVID-19. On the flight from Milan, Italy, to South Korea, she wore an N95 mask, except when she used a toilet. The toilet was shared by passengers sitting nearby, including an asymptomatic patient. She was seated 3 rows away from the asymptomatic patient (Figure). Given that she did not go outside and had self-quarantined for 3 weeks alone at her home in Italy before the flight and did not use public transportation to get to the airport, it is highly likely that her infection was transmitted in the flight via indirect contact with an asymptomatic patient. She reported coughing, rhinorrhea, and myalgia on quarantine day 8 and was transferred to a hospital on quarantine day 14. The remaining 292 passengers were released from quarantine on day 15.


Cohort study of severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2) transmission on evacuation flight from Milan, Italy, to Incheon, South Korea, on March 31, 2020. Red indicates asymptomatic patients who tested positive on quarantine day 1 (April 1, 2020); blue indicates asymptomatic patient who tested positive on quarantine day 14 (April 15, 2020). A) Timeline of flight, passenger quarantine, and testing protocol. B) Location of 6 asymptomatic patients and subsequently infected patient on flight. C) Case report of patient apparently infected during evacuation flight.

All crew members (n = 10) and medical staff dispatched from KCDC (n = 8) were quarantined at a government quarantine facility for 2 weeks and were tested twice for SARS-CoV-2, on quarantine days 1 and 14. All 18 members of the cabin crew and medical staff were negative for SARS-CoV-2 on both occasions.

To reinforce our results, we performed an external validation using a different dataset. Another evacuation flight of 205 passengers from Milan, Italy, to South Korea on April 3, 2020, was also conducted by KCDC under strict infection control procedures. Among the passengers on this flight were 3 asymptomatic patients who tested positive on quarantine day 1 and 1 patient who tested negative on quarantine day 1 and positive on quarantine day 14. On the basis of an epidemiologic investigation, the authors and KCDC suspect that this infection was also transmitted by inflight contact.