Transmission of SARS-CoV-2 associated with aircraft travel: A systematic review.

Rationale for the review: Air travel may be associated with viruses spread via infected passengers and potentially through in-flight transmission. Given the novelty of the SARS-CoV-2 virus, transmission associated with air travel is based on transmission dynamics of other respiratory viruses. Our objective was to provide a rapid summary and evaluation of relevant data on SARS-CoV-2 transmission aboard aircraft, report policy implications, and highlight research gaps requiring urgent attention. METHODS: We searched four electronic databases (1 February 2020 to 27 January 2021) and included studies on SARS-CoV-2 transmission aboard aircraft. We assessed study quality based on five criteria and reported important findings. KEY FINDINGS: We included 18 studies on in-flight SARS-CoV-2 transmission (130 unique flights) and two studies on wastewater from aircraft. The quality of evidence from most published studies was low. Two wastewater studies reported PCR-positive samples with high Cycle threshold values (33-39). Index case definition was heterogeneous across studies. The proportion of contacts traced ranged from 0.68% to 100%. Authors traced 2800/19729 passengers, 140/180 crew members, and 8/8 medical staff. Altogether, 273 index cases were reported, with 64 secondary cases. Three studies, each investigating one flight, reported no secondary cases. Secondary attack rate among studies following up > 80% of passengers and crew (including data on ten flights) varied between 0-8.2%. The studies reported on the possibility of SARS-CoV-2 transmission from asymptomatic, pre-symptomatic, and symptomatic individuals. Two studies performed viral cultures with ten positive results. Genomic sequencing and phylogenetic analysis were performed in individuals from four flights. CONCLUSION: Current evidence suggests SARS-CoV-2 can be transmitted during aircraft travel, but published data do not permit any conclusive assessment of likelihood and extent. The variation in design and methodology restricts the comparison of findings across studies. Standardized guidelines for conducting and reporting future studies of transmission on aircraft should be developed.