key: cord-0939590-ckdbsn36 authors: Moreno, Teresa; María Pintó, Rosa; Bosch, Albert; Moreno, Natalia; Alastuey, Andrés; Cruz Minguillón, María; Anfruns-Estrada, Eduard; Guix, Susana; Fuentes, Cristina; Buonanno, Giorgio; Stabile, Luca; Morawska, Lidia; Querol, Xavier title: Tracing surface and airborne SARS-CoV-2 RNA inside public buses and subway trains date: 2020-12-09 journal: Environ Int DOI: 10.1016/j.envint.2020.106326 sha: 187c5775d4ab23a984d1cc274e1476fb5854ca75 doc_id: 939590 cord_uid: ckdbsn36 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. demonstrated by a case of COVID-19 infection between private bus passengers during a day trip to a 108 religious event in January 2020 (Shen et al., 2020) , although this occurred just before widespread 109 pandemic awareness and so the passengers travelled unprotected by masks or disinfection (Table S1 ). The instruments operated at 10 L/min with Leland pumps placed 159 inside the driver's cabin and connected to filters placed above the closed access door to the driver 160 area on the passenger side ( Figure 1b) . Sampling was carried out simultaneously on two trains on the 161 same line for 9-10 hours of train running (Table S1) Additionally, three samples from each air conditioning (a/c) filter in six buses were collected. In 190 three of these six buses, samples of dust from immediately behind the a/c filter were also collected 191 (Table S1) . Finally, ambient air particles (PM 2.5 ) were collected during the entire bus work day from further six buses operating on the June 3 to 5, 2020 (two buses per day; routes selected by TMB) using the 198 same protocol described to this end for the subway (Figure 1d , where IVRR (h -1 ) represents the infectious virus removal rate in the space investigated, • evaluation of the dose of quanta (Dq) of the exposed subjects as: where T is the total exposure time of the exposed subjects and IR is their inhalation rate (IR) which is (Table 3) . The fact that a minority of the previously RNA positive samples still showed some RNA traces 340 suggests that the disinfection/cleaning procedure was not totally effective in removing the RNA. In 341 this context, it is also possible that the time elapsed between the sampling events before and after 342 cleaning/maintenance could have played a role in weakening the RNA signals but evidence for this is 343 unclear: Figure The average probability of infection, individual infectious risk, and basic reproduction for people 409 exposed in the six scenarios (and corresponding sub-scenarios) simulated are shown in Whereas no evidence for RNA traces was found in the small number of subway train a/c filters 443 examined, this was not the case for the bus a/c filter and dust samples, which showed evidence for 444 SARS-CoV-2 RNA in 4 out of 9 samples. There was a notable decrease in RNA traces detected after the bus cleaning/maintenance period. All samples disinfected using bleach proved free of the viral genome after cleaning, but this was not the case with all buses disinfected using ozone. 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Average probability of infection, basic reproduction number, and individual infectious risk for people susceptible people exposed in the six scenarios simulated. a) speaking; b) oral breathing.  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 Geospatial Resolution of Human and Bacterial Diversity 505 with City-Scale Metagenomics Recognizing and controlling airborne transmission of SARS-CoV-2 in indoor 507 environments SARS-CoV-2 (COVID-19) by the numbers. eLife Increasing Temperature and Relative Humidity 511 Accelerates Inactivation of SARS-CoV-2 on Surfaces Estimation of airborne viral emission: quanta emission 514 rate of SARS-CoV-2 for infection risk assessment Quantitative assessment of the risk of airborne 517 transmission of SARS-CoV-2 infection: prospective and retrospective applications Assessment of the impact of particulate dry deposition on 520 soiling of indoor cultural heritage objects found in churches and museums/libraries Detection of air and surface contamination by SARS-CoV-2 in hospital rooms of infected 526 patients Stability of 528 SARS-CoV-2 in different environmental conditions Physical distancing, face masks, 531 and eye protection to prevent person-to-person transmission of SARS-CoV-2 and COVID-19: a 532 systematic review and meta-analysis Bioaerosol 535 Sampling for Respiratory Viruses in Singapore's Mass Rapid Transit Network. 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Correctly fitted face masks are by now obligatory on public transport, and people are increasingly 485 aware that remaining silent whilst travelling is likely to reduce the risk of aerosol transmission. Table S1 . Samples collected in surfaces and air inside public buses and subway trains in Barcelona. ☒ The authors declare that they have no known competing financial interests or personal relationships that could have appeared to influence the work reported in this paper.☐The authors declare the following financial interests/personal relationships which may be considered as potential competing interests: