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      Can a toilet promote virus transmission? From a fluid dynamics perspective

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      1,2 , 1,3 , a) , 1,2
      Physics of Fluids
      AIP Publishing LLC

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          Abstract

          Currently, a novel coronavirus named “SARS-CoV-2” is spreading rapidly across the world, causing a public health crisis, economic losses, and panic. Fecal–oral transmission is a common transmission route for many viruses, including SARS-CoV-2. Blocking the path of fecal–oral transmission, which occurs commonly in toilet usage, is of fundamental importance in suppressing the spread of viruses. However, to date, efforts at improving sanitary safety in toilet use have been insufficient. It is clear from daily experience that flushing a toilet generates strong turbulence within the bowl. Will this flushing-induced turbulent flow expel aerosol particles containing viruses out of the bowl? This paper adopts computational fluid dynamics to explore and visualize the characteristics of fluid flow during toilet flushing and the influence of flushing on the spread of virus aerosol particles. The volume-of-fluid (VOF) model is used to simulate two common flushing processes (single-inlet flushing and annular flushing), and the VOF–discrete phase model (DPM) method is used to model the trajectories of aerosol particles during flushing. The simulation results are alarming in that massive upward transport of virus particles is observed, with 40%–60% of particles reaching above the toilet seat, leading to large-scale virus spread. Suggestions concerning safer toilet use and recommendations for a better toilet design are also provided.

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          Most cited references34

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          A rapid advice guideline for the diagnosis and treatment of 2019 novel coronavirus (2019-nCoV) infected pneumonia (standard version)

          In December 2019, a new type viral pneumonia cases occurred in Wuhan, Hubei Province; and then named “2019 novel coronavirus (2019-nCoV)” by the World Health Organization (WHO) on 12 January 2020. For it is a never been experienced respiratory disease before and with infection ability widely and quickly, it attracted the world’s attention but without treatment and control manual. For the request from frontline clinicians and public health professionals of 2019-nCoV infected pneumonia management, an evidence-based guideline urgently needs to be developed. Therefore, we drafted this guideline according to the rapid advice guidelines methodology and general rules of WHO guideline development; we also added the first-hand management data of Zhongnan Hospital of Wuhan University. This guideline includes the guideline methodology, epidemiological characteristics, disease screening and population prevention, diagnosis, treatment and control (including traditional Chinese Medicine), nosocomial infection prevention and control, and disease nursing of the 2019-nCoV. Moreover, we also provide a whole process of a successful treatment case of the severe 2019-nCoV infected pneumonia and experience and lessons of hospital rescue for 2019-nCoV infections. This rapid advice guideline is suitable for the first frontline doctors and nurses, managers of hospitals and healthcare sections, community residents, public health persons, relevant researchers, and all person who are interested in the 2019-nCoV.
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            Prolonged presence of SARS-CoV-2 viral RNA in faecal samples

            We present severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2) real-time RT-PCR results of all respiratory and faecal samples from patients with coronavirus disease 2019 (COVID-19) at the Fifth Affiliated Hospital of Sun Yat-sen University, Zhuhai, China, throughout the course of their illness and obligated quarantine period. Real-time RT-PCR was used to detect COVID-19 following the recommended protocol (appendix p 1). Patients with suspected SARS-CoV-2 were confirmed after two sequential positive respiratory tract sample results. Respiratory and faecal samples were collected every 1–2 days (depending on the availability of faecal samples) until two sequential negative results were obtained. We reviewed patients' demographic information, underlying diseases, clinical indices, and treatments from their official medical records. The study was approved by the Medical Ethical Committee of The Fifth Affiliated Hospital of Sun Yat-sen University (approval number K162-1) and informed consent was obtained from participants. Notably, patients who met discharge criteria were allowed to stay in hospital for extended observation and health care. Between Jan 16 and March 15, 2020, we enrolled 98 patients. Both respiratory and faecal samples were collected from 74 (76%) patients. Faecal samples from 33 (45%) of 74 patients were negative for SARS CoV-2 RNA, while their respiratory swabs remained positive for a mean of 15·4 days (SD 6·7) from first symptom onset. Of the 41 (55%) of 74 patients with faecal samples that were positive for SARS-CoV-2 RNA, respiratory samples remained positive for SARS-CoV-2 RNA for a mean of 16·7 days (SD 6·7) and faecal samples remained positive for a mean of 27·9 days (10·7) after first symptom onset (ie, for a mean of 11·2 days [9·2] longer than for respiratory samples). The full disease course of the 41 patients with faecal samples that were positive for SARS-CoV-2 RNA is shown in the figure . Notably, patient 1 had positive faecal samples for 33 days continuously after the respiratory samples became negative, and patient 4 tested positive for SARS-CoV-2 RNA in their faecal sample for 47 days after first symptom onset (appendix pp 4–5). Figure Timeline of results from throat swabs and faecal samples through the course of disease for 41 patients with SARS-CoV-2 RNA positive faecal samples, January to March, 2020 A summary of clinical symptoms and medical treatments is shown in the appendix (pp 2–3, 6–8). The presence of gastrointestinal symptoms was not associated with faecal sample viral RNA positivity (p=0·45); disease severity was not associated with extended duration of faecal sample viral RNA positivity (p=0·60); however, antiviral treatment was positively associated with the presence of viral RNA in faecal samples (p=0·025; appendix pp 2–3). These associations should be interpreted with caution because of the possibility of confounding. Additionally, the Ct values of all three targeted genes (RdRp, N, E) in the first faecal sample that was positive for viral RNA were negatively associated with the duration of faecal viral RNA positivity (RdRp gene r= –0·34; N gene r= –0·02; and E gene r= –0·16), whereas the correlation of the Ct values with duration of faecal sample positivity was only significant for RdRp (p=0·033; N gene p=0·91; E gene p=0·33). Our data suggest the possibility of extended duration of viral shedding in faeces, for nearly 5 weeks after the patients' respiratory samples tested negative for SARS-CoV-2 RNA. Although knowledge about the viability of SARS-CoV-2 is limited, 1 the virus could remain viable in the environment for days, which could lead to faecal–oral transmission, as seen with severe acute respiratory virus CoV and Middle East respiratory syndrome CoV. 2 Therefore, routine stool sample testing with real-time RT-PCR is highly recommended after the clearance of viral RNA in a patient's respiratory samples. Strict precautions to prevent transmission should be taken for patients who are in hospital or self-quarantined if their faecal samples test positive. As with any new infectious disease, case definition evolves rapidly as knowledge of the disease accrues. Our data suggest that faecal sample positivity for SARS-CoV-2 RNA normally lags behind that of respiratory tract samples; therefore, we do not suggest the addition of testing of faecal samples to the existing diagnostic procedures for COVID-19. However, the decision on when to discontinue precautions to prevent transmission in patients who have recovered from COVID-19 is crucial for management of medical resources. We would suggest the addition of faecal testing for SARS-CoV-2. 3 Presently, the decision to discharge a patient is made if they show no relevant symptoms and at least two sequential negative results by real-time RT-PCR of sputum or respiratory tract samples collected more than 24 h apart. Here, we observed that for over half of patients, their faecal samples remained positive for SARS-CoV-2 RNA for a mean of 11·2 days after respiratory tract samples became negative for SARS-CoV-2 RNA, implying that the virus is actively replicating in the patient's gastrointestinal tract and that faecal–oral transmission could occur after viral clearance in the respiratory tract. Determining whether a virus is viable using nucleic acid detection is difficult; further research using fresh stool samples at later timepoints in patients with extended duration of faecal sample positivity is required to define transmission potential. Additionally, we found patients normally had no or very mild symptoms after respiratory tract sample results became negative (data not shown); however, asymptomatic transmission has been reported. 4 No cases of transmission via the faecal–oral route have yet been reported for SARS-CoV-2, which might suggest that infection via this route is unlikely in quarantine facilities, in hospital, or while under self-isolation. However, potential faecal–oral transmission might pose an increased risk in contained living premises such as hostels, dormitories, trains, buses, and cruise ships. Respiratory transmission is still the primary route for SARS-CoV-2 and evidence is not yet sufficient to develop practical measures for the group of patients with negative respiratory tract sample results but positive faecal samples. Further research into the viability and infectivity of SARS-CoV-2 in faeces is required.
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              COVID-19: Gastrointestinal Manifestations and Potential Fecal–Oral Transmission

              The outbreak of novel coronavirus (2019-nCoV) pneumonia initially developed in one of the largest cities, Wuhan, Hubei province of China, in early December 2019 and has been declared the sixth public health emergency of international concern by the World Health Organization, and subsequently named coronavirus disease 2019 (COVID-19). As of February 20, 2020, a total of >75,000 cumulative confirmed cases and 2130 deaths have been documented globally in 26 countries across 5 continents. Current studies reveal that respiratory symptoms of COVID-19 such as fever, dry cough, and even dyspnea represent the most common manifestations at presentation similar to severe acute respiratory syndrome (SARS) in 2003 and Middle East respiratory syndrome in 2012, which is firmly indicative of droplet transmission and contact transmission. However, the incidence of less common features like diarrhea, nausea, vomiting, and abdominal discomfort varies significantly among different study populations, along with an early and mild onset frequently followed by typical respiratory symptoms. 1 Mounting evidence from former studies of SARS indicated that the gastrointestinal tract (intestine) tropism of SARS coronavirus (SARS-CoV) was verified by the viral detection in biopsy specimens and stool even in discharged patients, which may partially provide explanations for the gastrointestinal symptoms, potential recurrence, and transmission of SARS from persistently shedding human as well. 2 Notably, the first case of 2019-nCoV infection confirmed in the United States reported a 2-day history of nausea and vomiting on admission, and then passed a loose bowel movement on hospital day 2. The viral nucleic acids of loose stool and both respiratory specimens later tested positive. 3 In addition, 2019-nCoV sequence could be also detected in the self-collected saliva of most infected patients even not in nasopharyngeal aspirate, and serial saliva specimens monitoring showed declines of salivary viral load after hospitalization. 4 Given that extrapulmonary detection of viral RNA does not mean infectious virus is present, further positive viral culture suggests the possibility of salivary gland infection and possible transmission. 4 More recently, 2 independent laboratories from China declared that they have successfully isolated live 2019-nCoV from the stool of patients (unpublished). Taken together, a growing number of clinical evidence reminds us that digestive system other than respiratory system may serve as an alternative route of infection when people are in contact with infected wild animals or sufferers, and asymptomatic carriers or individuals with mild enteric symptoms at an early stage must have been neglected or underestimated in previous investigations. Clinicians should be careful to promptly identify the patients with initial gastrointestinal symptoms and explore the duration of infectivity with delayed viral conversion. To date, molecular modelling has revealed by the next-generation sequencing technology that 2019-nCoV shares about 79% sequence identify with SARS-CoV, indicative of these 2 lineage B β-coronaviruses highly homologous, and angiotensin-converting enzyme II (ACE2), previously known as an entry receptor for SARS-CoV, was exclusively confirmed in 2019-nCoV infection despite amino acid mutations at some key receptor-binding domains. 5 , 6 It is widely accepted that coronavirus human transmissibility and pathogenesis mainly depend on the interactions, including virus attachment, receptor recognition, protease cleaving and membrane fusion, of its transmembrane spike glycoprotein (S-protein) receptor-binding domain, specific cell receptors (ACE2), and host cellular transmembrane serine protease (TMPRSS), with binding affinity of 2019-nCoV about 73% of SARS-CoV. 7 Recent bioinformatics analysis on available single-cell transcriptomes data of normal human lung and gastrointestinal system was carried out to identify the ACE2-expressing cell composition and proportion, and revealed that ACE2 was not only highly expressed in the lung AT2 cells, but also in esophagus upper and stratified epithelial cells and absorptive enterocytes from ileum and colon. 8 With the increasing gastrointestinal wall permeability to foreign pathogens once virus infected, enteric symptoms like diarrhea will occur by the invaded enterocytes malabsorption, which in theory indicated the digestive system might be vulnerable to COVID-19 infection. In contrast, because ACE2 and TMPRSS especially TMPRSS2 are co-localized in the same host cells and the latter exerts hydrolytic effects responsible for S-protein priming and viral entry into target cells, further bioinformatics investigation renders additional evidence for enteric infectivity of COVID-19 in that the high co-expression ratio was found in absorptive enterocytes and upper epithelial cells of esophagus besides lung AT2 cells. However, the exact mechanism of COVID-19–induced gastrointestinal symptom largely remains elusive. Based on these considerations, ACE2-based strategies against COVID-19 such as ACE2 fusion proteins and TMPRSS2 inhibitors should be accelerated into clinical research and development for diagnosis, prophylaxis, or treatment. Last, mild to moderate liver injury, including elevated aminotransferases, hypoproteinemia, and prothrombin time prolongation, has been reported in the existing clinical investigations of COVID-19, whereas up to 60% of patients suffering from SARS had liver impairment. The presence of viral nucleic acids of SARS in liver tissue confirmed the coronavirus direct infection in liver, and percutaneous liver biopsies of SARS showed conspicuous mitoses and apoptosis along with atypical features such as acidophilic bodies, ballooning of hepatocytes, and lobular activities without fibrin deposition or fibrosis. 9 It is believed that SARS-associated hepatotoxicity may be likely with viral hepatitis or a secondary effect associated with drug toxicity owing to high-dose consumption of antiviral medications, antibiotics, and steroids, as well as immune system overreaction. However, little is known about 2019-nCoV infection in liver. Surprisingly, recent single cell RNA sequencing data from 2 independent cohorts revealed a significant enrichment of ACE2 expression in cholangiocytes (59.7% of cells) instead of hepatocytes (2.6% of cells), suggesting that 2019-nCoV might lead to direct damage to the intrahepatic bile ducts. 10 Altogether, substantial effort should be made to be alert on the initial digestive symptoms of COVID-19 for early detection, early diagnosis, early isolation, and early intervention.
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                Author and article information

                Contributors
                Journal
                Phys Fluids (1994)
                Phys Fluids (1994)
                PHFLE6
                Physics of Fluids
                AIP Publishing LLC
                1070-6631
                1089-7666
                01 June 2020
                16 June 2020
                : 32
                : 6
                : 065107
                Affiliations
                [1 ]Key Laboratory of Energy Thermal Conversion and Control of Ministry of Education, School of Energy and Environment, Southeast University , Nanjing 210096, People’s Republic of China
                [2 ]Jiangsu Key Laboratory of Micro and Nano Heat Fluid Flow Technology and Energy Application, School of Environmental Science and Engineering, Suzhou University of Science and Technology , Suzhou 215009, People’s Republic of China
                [3 ]College of Electrical, Energy and Power Engineering, Yangzhou University , Yangzhou 225009, People’s Republic of China
                Author notes
                [a) ]Author to whom correspondence should be addressed: j.x.wang@ 123456yzu.edu.cn
                Author information
                http://orcid.org/0000-0002-5965-1356
                Article
                5.0013318 POF20-AR-01316
                10.1063/5.0013318
                7301880
                32574232
                fd1874c5-718b-48fc-9f45-8fbf767a73aa
                Copyright © 2020 Author(s)

                Published under license by AIP Publishing.

                1070-6631/2020/32(6)/065107/14/ $30.00

                All article content, except where otherwise noted, is licensed under a Creative Commons Attribution (CC BY) license ( http://creativecommons.org/licenses/by/4.0/).

                History
                : 15 May 2020
                : 21 May 2020
                Page count
                Pages: 14
                Funding
                Funded by: National Natural Science Foundation of China http://dx.doi.org/10.13039/501100001809
                Award ID: 51725602
                Award ID: 51876184
                Categories
                ARTICLES
                Turbulent Flows
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