key: cord-0932397-4oavfu6t authors: Heller, Léo; Mota, César R.; Greco, Dirceu B. title: COVID-19 faecal-oral transmission: Are we asking the right questions? date: 2020-04-25 journal: Sci Total Environ DOI: 10.1016/j.scitotenv.2020.138919 sha: 6ec2e029620323bcf0e94950b0e866e495396fbc doc_id: 932397 cord_uid: 4oavfu6t Abstract Detection of the SARS-CoV-2 virus in stools and sewage has recently been reported, raising the hypothesis of faecal-oral transmission. If confirmed, this could have far-reaching consequences for public health and for pandemic control strategies. In this paper, we argue that a comprehensive and more nuanced analysis is required to test this hypothesis, taking into consideration both taking into consideration both environmental dynamics and the persistence of viral infectivity. First, we examine the evidence regarding the presence of the virus in stools and sewage. Then we discuss the current framework of disease transmission through water and excreta and how the transmission of a respiratory disease fits into it. Against this background, we propose a framework to test the faecal-oral hypothesis, unpacking the different environmental routes from faeces to the mouth of a susceptible person. This framework should not be seen as a confirmation of the hypothesis but rather as an expanded view of its complexities, which could help shaping an agenda for research into a number of unanswered questions. Finally, the paper briefly discusses practical implications, based on current knowledge, for containment of the pandemic. The SARS-CoV-2 virus, the etiological agent of COVI-19, is primarily transmitted through respiratory droplets and contact routes (WHO 2020) . This virus uses angiotensin-converting enzyme ACE2 as a receptor to enter human cells (Xu et al. 2020 ) and ACE2 messenger RNA is highly expressed in the gastrointestinal system (Harmer et al. 2002) . Detection of viable SARS-CoV-2 in stools of COVID-19 patients has been reported (Wu et al. 2020 , Hindson, 2020 and virus RNA has been found in sewage (Medema et al. 2020 , Ahmed et al 2020 , raising the possibility of faecal-oral transmission. COVID-19 patients can shed the virus in faeces for days after all respiratory symptoms have disappeared (Wu et al. 2020) . However, persistence of viable SARS-Cov-2 in water and sewage has yet to be determined. A study with other coronaviruses demonstrated a 99.9% die-off of 10 days in tap water at 23 o C and over 100 days at 4 o C. In sewage, the time to achieve a 99.9% die-off ranged from 2 to 3 days at 23 o C (Gundy et al. 2009 ). Persistence of human coronaviruses on surfaces is highly variable (from 2 hours to 9 days), depending on temperature, humidity, type of surface, and virus strain (Kampf et al. 2020) . Moreover, several human coronaviruses have been shown to be particularly sensitive to water chlorination. If confirmed, the "faecal-oral hypothesis" for COVID-19 may result in far-reaching consequences for public health and for pandemic control strategies. However, a Journal Pre-proof J o u r n a l P r e -p r o o f 3 comprehensive and more nuanced analysis is required to test this hypothesis, taking into consideration both environmental dynamics and the persistence of viral infectivity. In a seminal study, White et al. (1972) assessed disease transmission routes for water-related hazards and classified them into four categories. Two of them may be of especial relevance for COVID-19: (i) WATER1: water-borne, in which transmission occurs by ingestion of a pathogen present in water, and water acts as a passive vehicle for the infecting agent; and (ii) WATER2: water-washed, in which infection can be prevented by the provision of sufficient water for domestic and personal hygiene. Excreta-related diseases are classified into six categories (Feachem et al. 1983 ). Two of them may be relevant to the current pandemic. SANITATION1 includes faecal-oral (non-bacterium) infections, characterised by agents of low infective doses, including enteroviruses (polio-, echo-, and coxsackievirus), hepatitis A and rotavirus, which can easily spread when domestic or personal hygiene is inadequate. For this route, excreta disposal has limited effect on the incidence of infections if it is disconnected from thorough changes in personal cleanliness, which requires major improvements in water supply, housing, and health education. Another The role of water in the transmission of respiratory infectious diseases was suggested decades after the original classification of water-related diseases. However, the focus was mainly on the protective effect of handwashing (Cairncross 2003, Fung and Cairncross 2006) . Recently, a fifth category of water-related diseases was proposed (Bartram and Hunter 2015) : WATER5: J o u r n a l P r e -p r o o f First confirmed detection of SARS-CoV-2 in untreated wastewater in Australia: A proof of concept for the wastewater surveillance of COVID-19 in the community Bradley Classification of disease transmission routes for water-related hazards Editorial: Handwashing with soap -a new way to prevent ARIs? 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