COVID-19 infection among international travellers: a prospective analysis

• Published in: BMJ open Vol. 11; no. 6; p. e050667
• Main Authors: Lunney, Meaghan, Ronksley, Paul E, Weaver, Robert G, Barnieh, Lianne, Blue, Norman, Avey, Marc T, Rolland-Harris, Elizabeth, Khan, Faisal M, Pang, Jack X Q, Rafferty, Ellen, Scory, Tayler D, Svenson, Lawrence W, Rodin, Rachel, Tonelli, Marcello
• Format: Journal Article
• Language: English
• Published: England BMJ Publishing Group LTD 24.06.2021; BMJ Publishing Group
• Series: Original research
• Subjects: Alberta - epidemiology; Asymptomatic; Coronaviruses; COVID-19; COVID-19 - diagnosis; COVID-19 diagnostic tests; COVID-19 Testing; Disease transmission; Fines & penalties; Households; Humans; Infections; Infectious Diseases; Internationality; Personal health; Prospective Studies; Public health; Quarantine; SARS-CoV-2; Severe acute respiratory syndrome coronavirus 2; Travel; Alberta; Canada; COVID-19; public health; health policy
• ISSN: 2044-6055; 2044-6055
• DOI: 10.1136/bmjopen-2021-050667

ObjectivesThis report estimates the risk of COVID-19 importation and secondary transmission associated with a modified quarantine programme in Canada.Design and participantsProspective analysis of international asymptomatic travellers entering Alberta, Canada.InterventionsAll participants were required to receive a PCR COVID-19 test on arrival. If negative, participants could leave quarantine but were required to have a second test 6 or 7 days after arrival. If the arrival test was positive, participants were required to remain in quarantine for 14 days.Main outcome measuresProportion and rate of participants testing positive for COVID-19; number of cases of secondary transmission.ResultsThe analysis included 9535 international travellers entering Alberta by air (N=8398) or land (N=1137) that voluntarily enrolled in the Alberta Border Testing Pilot Programme (a subset of all travellers); most (83.1%) were Canadian citizens. Among the 9310 participants who received at least one test, 200 (21.5 per 1000, 95% CI 18.6 to 24.6) tested positive. Sixty-nine per cent (138/200) of positive tests were detected on arrival (14.8 per 1000 travellers, 95% CI 12.5 to 17.5). 62 cases (6.7 per 1000 travellers, 95% CI 5.1 to 8.5; 31.0% of positive cases) were identified among participants that had been released from quarantine following a negative test result on arrival. Of 192 participants who developed symptoms, 51 (26.6%) tested positive after arrival. Among participants with positive tests, four (2.0%) were hospitalised for COVID-19; none required critical care or died. Contact tracing among participants who tested positive identified 200 contacts; of 88 contacts tested, 22 were cases of secondary transmission (14 from those testing positive on arrival and 8 from those testing positive thereafter). SARS-CoV-2 B.1.1.7 lineage was not detected in any of the 200 positive cases.Conclusions21.5 per 1000 international travellers tested positive for COVID-19. Most (69%) tested positive on arrival and 31% tested positive during follow-up. These findings suggest the need for ongoing vigilance in travellers testing negative on arrival and highlight the value of follow-up testing and contact tracing to monitor and limit secondary transmission where possible.