PLEASE NOTE: This article is science-based but poses lay questions regarding its implications. It is shared openly to invite reflection by public health experts and policy-makers, and will be updated to reflect the relevant responses and developments.
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Evidence that COVID-19 virus can be excreted ‘live’ has led researchers to warn against ignoring the risk of faecal-oral transmission.
Despite the apparently significant implications for both disease management and preventive health (hygiene protocols), there seems to be no general awareness of the issue, nor is it reflected in public health strategies and guidance.
What follows is to invite public health experts and policy-makers to consider the issues and help answer the key questions listed at the end.
The science:
Researchers assessing known transmission routes of the novel coronavirus SARS-CoV-2 have reported that the virus has been found to be excreted live in faeces, leading them to warn that, as a result, “the faecal-oral mode of transmission … cannot be ignored”.
As well as highlighting the “high infectivity” of spread from the respiratory tract; and the potential for contamination from common sites in residential settings, such as cellphones and door handles, the paper ‘Uncertainties about the transmission routes of 2019 novel coronavirus’ (https://onlinelibrary.wiley.com/doi/full/10.1111/irv.12735, published in ‘Influenza and other respiratory viruses’, Wiley Online Library, March 2020, accessed online 18 April 2020) also notes that “the existence of live SARS-CoV-2 in stool has been confirmed”.
“The phenomenon is coincident with that of SARS-CoV, as a result of ACE2 highly expressing in epithelia of the small intestine”, explain co-lead authors Qingmei Han and Qingqing Lin, of Zhejiang University, in Hangzhou, China, citing the findings of research teams from “two key independent state laboratories”.
The paper also notes the proven role of sewage-borne coronavirus in the 2002-03 SARS epidemic – an outbreak involving 321 people in a single Hong Kong high-rise housing estate, they say – and the relevance of that situation to SARS-CoV-2: “Sewage is considered to play a definite role in this transmission.”
“In summary, the faecal-oral or faecal-droplet mode of transmission may be one of several routes and cannot be ignored,” they conclude. “More efforts must be made to get the full picture of transmission, so that public health measures can be adopted in a timely manner to reduce further spread, within China and beyond.”
Considerations:
In a nutshell, aside from the more technical virological and epidemiological questions, my non-expert facts-based concern is essentially for this: If mildly symptomatic or asymptomatic (and, importantly: non-fatal) high viral loads are being incubated intestinally and shed anally (in principle, over a longer period than occurs in the upper airways or lungs), then it must follow that (whatever the risk of pathogenic faecal-oral self-retransmission too) faecal viral shedding poses, at the very least, a significant risk of contagiousness to others, and for a longer period.
The current official hygiene-related guidance focuses almost exclusively on thorough and frequent hand-washing, as well as avoiding touching our face, eyes, nose or mouth, particularly in public settings, given the greater risk of exposure to coronavirus-contaminated surfaces.
However, in the ‘safe’ environment of the home – among non-exposed, asymptomatic family members – the general perception is that, having taken care to clean commonly-handled objects – cellphones, keys, door knobs, etc – the only risk of COVID-19 infection comes from the world outside, ie via goods that enter the home, notably packaging.
In terms of personal hygiene, while you’d expect people to always wash their hands after defecating or nappy-changing, for example, there is no public awareness of the risk of transmission through faeces, nor, therefore, of the need for an equally thorough approach to hand-washing in these home-based situations, as a means to ensuring that the home environment really is as coronavirus-free as one might think.
The known facts also suggest that there is a risk of anal viral shedding which a paper wipe alone will not account for. Surely, hygiene protocols should therefore also reflect the need for similarly thorough hygiene to account for this. Similarly, shouldn’t there be more public awareness of the risk of transmission from soiled clothes, for example?
The epidemiological and immunological implications of the faecal transmission route is a question for the experts, of course. At least, according to the said researchers, we cannot ignore its potential role in any given case or outbreak. So, I wonder whether the risk of transmission from intestinal incubation should mean longer self-isolation protocols. Also, might intestinal incubation explain outbreaks where transmission rates and timelines appear to persist beyond what you would expect from a strict lockdown, for example?
For now, in terms of public health policy, the existence of a faecal route must surely have direct implications for strategies aimed at interrupting transmission, mainly in terms of personal hygiene guidance, very especially in parts of the world with less-developed sanitary infrastructures.
Key questions:
- To what extent might intestinal incubation: (a) explain delays in the onset of symptoms; (b) affect the immune response; and/or (c) result in unexpectedly long transmission timelines?
- To what extent might such cases be missed by nasopharyngeal swab testing (eg will intestinal incubation always be accompanied by significant viral load in the upper airways)?
- What transmission risk might ‘silent’ intestinal incubation pose (eg in family and ‘co-residential’ settings perceived as eminently safe under current hygiene and self-isolation protocols)?
- Should personal hygiene protocols (ie anal, as well as hand washing) be revised to account for these implications?
- How much more relevant and urgent are these considerations in parts of the world with less-developed sanitary infrastructures (especially in the light of the evidence of sewage-borne SARS outbreaks)?
Bernard Murphy
(Contact: Please leave a comment here, or respond/message via Twitter @medtech_BM or @KernelMeollo )
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