Skip to main content
In response to Wendy Glauser’s article, Communication, transparency key as Canada faces new coronavirus threat, we would like to share the public health response to the first Canadian cases of COVID-19. Case details have been published.(1) The patients traveled from Wuhan to Guangzhou, then Guangzhou to Toronto, Canada, arriving on January 22, 2020. The index patient was symptomatic with dry cough during the flight. His wife developed cough on January 23rd. Both sets of throat and nasopharyngeal swabs collected were positive for COVID-19.
There were approximately 350 passengers on board the airplane. The public was notified through the media that the index case was symptomatic during the 15-hour flight. Close contacts included 25 individuals sitting within two meters of the index case during the flight, flight crew members, and one close contact on arrival in Toronto. Close contacts received active daily contact monitoring by local public health officials for 14 days from the flight. Passengers and crew members who were not from Ontario were referred to their home jurisdiction for follow-up. On January 29th, one close contact developed symptoms of cough; however, nasopharyngeal and throat swabs were negative for COVID-19. Non-close contact passengers were advised to self-monitor and contact public health if symptomatic; five non-close contact symptomatic passengers were tested and found negative by nasopharyngeal and throat swabs for COVID-19.
The United States Centers for Disease Control and Prevention recommends contact tracing two rows in front and behind symptomatic cases with respiratory infections due to an elevated risk within close contact.(2) However, for both SARS-CoV and influenza, approximately 50% of airplane transmission has occurred beyond these rows.(3) Studies of airplane transmission are commonly biased by contacts sharing exposure risks prior to boarding the aircraft.(4) In our investigation, transmission may have been mitigated by mild symptoms and masking during the flight. However, the lack of secondary cases after prolonged air travel exposure supports droplet transmission, not airborne, as the likely route of spread of the COVID-19.
References
1. Silverstein W, Stroud L, Cleghorn G, Leis J. First imported case of 2019 novel coronavirus to Canada presenting as mild pneumonia. Lancet. 2020. Lancet. 2020;EPub Feb 13.
2. Protecting Travelers' Health from Airport to Community: Investigating Contagious Diseases on Flights, Available online at: https://www.cdc.gov/quarantine/contact-investigation.html (accessed February 6, 2020).
3. Hertzberg VS, Weiss H. On the 2-Row Rule for Infectious Disease Transmission on Aircraft. Ann Glob Health. 2016;82:819-23.
4. Leitmeyer K, Adlhoch C. Review Article: Influenza Transmission on Aircraft: A Systematic Literature Review. Epidemiology (Cambridge, Mass.). 2016;27:743-51.