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

  1. Elena C Rosca
  2. Carl Heneghan
  3. Elizabeth A Spencer
  4. Jon Brassey
  5. Annette Plüddemann
  6. Igho J Onakpoya
  7. David H Evans
  8. John M Conly
  9. Tom Jefferson

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Abstract

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 Severe acute respiratory syndrome coronavirus 2 (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 to highlight research gaps requiring urgent attention.

Methods

We searched four electronic databases (1 February 2020–27 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 2 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 2800/19 729 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 10 flights) varied between 0 and 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 10 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.

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  1. Version published to 10.1093/jtm/taab133
  2. ScreenIT

    SciScore for 10.1101/2021.06.03.21258274: (What is this?)

    Please note, not all rigor criteria are appropriate for all manuscripts.

    Table 1: Rigor

    Ethicsnot detected.
    Sex as a biological variablenot detected.
    Randomizationnot detected.
    Blindingnot detected.
    Power Analysisnot detected.

    Table 2: Resources

    Software and Algorithms
    SentencesResources
    For this review we conducted searches in the following electronic databases: LitCovid, medRxiv, Google Scholar, and the WHO Covid-19 database up to 27 January 2021.
    Google Scholar
    suggested: (Google Scholar, RRID:SCR_008878)

    Results from OddPub: We did not detect open data. We also did not detect open code. Researchers are encouraged to share open data when possible (see Nature blog).

    Results from LimitationRecognizer: We detected the following sentences addressing limitations in the study:
    However, a major limitation of most studies consisted of the possibility of asymptomatic index cases transmitting the infection and of asymptomatic secondary cases not being investigated due to lack of any symptoms, with lowering the quality of case ascertainment. In addition, the number of studies that reported on Ct of RT-PCR is limited; therefore, case ascertainments are likely to be biased [Jefferson 2021]. The timeline of the sample collections also is suggestive of bias in some studies. The four studies that performed GS and phylogenetic analysis [Choi 2020; Murphy 2020; Speake 2020; Swadi 2021] report higher quality reliable evidence, indicating that aircraft may be a setting associated with SARS-CoV-2 transmission. GS alone cannot prove the presence of infectious materials, as the amplicon-based methods now often used to assemble SARS-CoV-2 genome sequences require only viral RNA. Nor can amplification-based SARS-CoV-2 sequencing exclude infections caused by other agents such as rhinoviruses and OC43. However, such methods do provide secure phylogenetic insights into the relationship between the putative index and secondary cases. Nonetheless, the use of databases like Global initiative on sharing all influenza data (GISAID) to ascertain transmission may induce bias. A recent review [Furuse, 2021] found that, even though many developing countries have high numbers of SARS-CoV-2 infected cases, they have few published sequences. Such missing data could create bias in a...

    Results from TrialIdentifier: No clinical trial numbers were referenced.

    Results from Barzooka: We did not find any issues relating to the usage of bar graphs.

    Results from JetFighter: We did not find any issues relating to colormaps.

    Results from rtransparent:
    • Thank you for including a conflict of interest statement. Authors are encouraged to include this statement when submitting to a journal.
    • Thank you for including a funding statement. Authors are encouraged to include this statement when submitting to a journal.
    • No protocol registration statement was detected.

    Results from scite Reference Check: We found no unreliable references.

    About SciScore

    SciScore is an automated tool that is designed to assist expert reviewers by finding and presenting formulaic information scattered throughout a paper in a standard, easy to digest format. SciScore checks for the presence and correctness of RRIDs (research resource identifiers), and for rigor criteria such as sex and investigator blinding. For details on the theoretical underpinning of rigor criteria and the tools shown here, including references cited, please follow this link.

  3. Version published to 10.1101/2021.06.03.21258274v1 on medRxiv