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      Tracing surface and airborne SARS-CoV-2 RNA inside public buses and subway trains

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          • Surface and air samples from buses and subway trains were PCR-tested for SARS-CoV-2.

          • Evidence for fragments of viral RNA was found in 30 out of 82 samples.

          • The potential infectivity of these samples however is considered to be extremely low.

          • The data emphasise the importance of disinfection and hygiene in public transport.

          • Modelling in-bus infection probability shows forced ventilation greatly reduces risk.


          Given the widespread concern but general lack of information over the possibility of SARS-CoV-2 infection in public transport, key issues such as passenger personal hygiene, efficient air circulation systems, and the effective disinfection of frequently touched surfaces need to be evaluated to educate the public and diminish the risk of viral transmission as we learn to live with the ongoing pandemic. In this context we report on a study involving the collection of 99 samples taken from inside Barcelona buses and subway trains in May to July 2020. From this sample group 82 (58 surface swabs, 9 air conditioning (a/c) filters, 3 a/c dust, 12 ambient air) were selected to be analysed by RT-PCR for traces of the SARS-CoV-2 virus. Thirty of these selected samples showed evidence for one or more of 3 target RNA gene regions specific for this virus (IP2, IP4, E). Most (24) of these 30 samples showed positivity for only 1 of the 3 RNA targets, 4 samples yielded 2 targets, and 2 samples provided evidence for all 3 targets. RNA remnants were more common in surface swabs from support bars (23 out of 58) than in ambient air inside the vehicles (3 out of 12), with relatively higher concentrations of viral RNA fragments in buses rather than in trains. Whereas subway train a/c filters examined were all virus-free, 4 of the 9 bus a/c filter/dust samples yielded evidence for viral RNA. After nocturnal maintenance and cleaning most buses initially yielding positive results subsequently showed elimination of the RT-PCR signal, although signs of viral RNA remained in 4 of 13 initially positive samples. The presence of such remnant viral traces however does not demonstrate infectivity, which in the present study is considered unlikely given the fragmentary nature of the gene targets detected. Nevertheless, best practice demands that regular vehicle disinfection in public transport worldwide needs to be rigorously ascertained to be effective at eliminating traces of the virus throughout the vehicle, especially at times when COVID-19 cases are peaking. Additionally, infectivity tests should be implemented to evaluate the efficiency of disinfection procedures to complement the information resulting from RT-PCR analysis. Modelling the probability of infection whilst travelling in buses under different scenarios indicates that forced ventilation greatly reduces the risk.

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          Author and article information

          Environ Int
          Environ Int
          Environment International
          The Author(s). Published by Elsevier Ltd.
          9 December 2020
          9 December 2020
          [a ]Institute of Environmental Assessment and Water Research (IDAEA). Consejo Superior de Investigaciones Científicas (CSIC). C/Jordi Girona, 18-26. 08034 Barcelona, Spain
          [b ]Enteric Virus Laboratory, Dep. Genetics, Microbiology and Statistics, University of Barcelona, Avda. Diagonal 643, 08028 Barcelona, Spain
          [c ]Department of Civil and Mechanical Engineering, University of Cassino and Southern Lazio, Cassino, Italy
          [d ]International Laboratory for Air Quality and Health, Queensland University of Technology, Brisbane, Australia
          Author notes
          [* ]Corresponding author.

          Equally contributed

          S0160-4120(20)32281-9 106326
          © 2020 The Author(s)

          Since January 2020 Elsevier has created a COVID-19 resource centre with free information in English and Mandarin on the novel coronavirus COVID-19. The COVID-19 resource centre is hosted on Elsevier Connect, the company's public news and information website. Elsevier hereby grants permission to make all its COVID-19-related research that is available on the COVID-19 resource centre - including this research content - immediately available in PubMed Central and other publicly funded repositories, such as the WHO COVID database with rights for unrestricted research re-use and analyses in any form or by any means with acknowledgement of the original source. These permissions are granted for free by Elsevier for as long as the COVID-19 resource centre remains active.


          rt-qpcr, sars-cov-2, covid-19, disinfection, public transport, ozone


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