Infectious SARS-CoV-2 has been isolated from the stool of a few COVID-19 patients worldwide. However, there are not yet published reports of infectious SARS-CoV-2 isolation from wastewater. While fecal-oral transmission via wastewater has been hypothesized, the empirical evidence indicates the probability is quite low. The basis for this assertion is summarized in the commentary “Differentiating between the possibility and probability of SARS-CoV-2 transmission associated with wastewater: empirical evidence is needed to substantiate risk” published in FEMS Microbes. Two authors of the study, Aaron Bivins and Warish Ahmed, discuss for the #FEMSmicroBlog how we need to remain focused on airborne transmission via respiratory shedding until empirical evidence establishes otherwise. #FascinatingMicrobes
SARS-CoV-2 in human feces?
So far, the novel coronavirus SARS-CoV-2 has infected over 150 million people worldwide during the ongoing COVID-19 pandemic. To end the transmission of this airborne agent, we need to efficiently use the limited resources available.
Primary transmission of SARS-CoV-2 seems to occur via respiratory shedding along the airborne route. Some studies suggested an associated intestinal infection on the basis of the prevalent shedding of SARS-CoV-2 RNA and the occasional isolation of infectious SARS-CoV-2 in the stool of COVID-19 patients. As a result, numerous reviews hypothesized that SARS-CoV-2 can be transmitted via the fecal-oral route and suggest that we need to divert resources for such intervention.
Establishing risk with empirical evidence
Research teams throughout the world are now measuring SARS-CoV-2 RNA in wastewater. This is to track COVID-19 trends in communities alongside clinical testing (COVIDPoops19 Dashboard).
There have only been 19 attempts to culture SARS-CoV-2 from wastewater, which were all unsuccessful. These are even fewer attempts than the number of reviews written on fecal-oral transmission.
As summarized in “Differentiating between the possibility and probability of SARS-CoV-2 transmission associated with wastewater: empirical evidence is needed to substantiate risk“, the limited empirical evidence suggests that the probability of SARS-CoV-2 transmission via the fecal-oral route is exceedingly low.
Yet, we cannot rule out transmission via wastewater aerosols. The available evidence indicates that such transmission is likely rare compared to well established respiratory shedding airborne routes. For example, a recent study of wastewater workers in Spain found that the prevalence of SARS-CoV-2 antibodies among them was no different than in the general population.
While these seem to be promising results, we need more empirical evidence of infectious SARS-CoV-2 in waste and environmental waters to further establish and quantify risks to human health. In the absence of such evidence, continued speculation regarding fecal-oral transmission does not better inform our response to the pandemic.
We need further pandemic precaution!
The often-cited precautionary principle dictates that before introducing a newly developed technology one needs to absolutely establish the potential for its harm.
But in this instance, the human population is not the actor but acted upon by a deadly zoonotic virus. To triage resources to fight COVID-19, we must consider the relative risk of transmission pathways, for example, wastewater versus respiratory shedding, rather than the absolute risk of any single pathway.
The ongoing response to the COVID-19 pandemic must remain centered on interrupting airborne transmission via respiratory shedding until evidence substantiates wastewater transmission!
We must focus on interrupting airborne transmission of SARS-CoV2 until evidence substantiates other transmission routes!
- Read the commentary “Differentiating between the possibility and probability of SARS-CoV-2 transmission associated with wastewater: empirical evidence is needed to substantiate risk” published in FEMS Microbes by Ahmed et al. (2021).
About the authors of this blog
Dr. Aaron Bivins is a post-doctoral research associate in the Department of Civil and Environmental Engineering and Earth Sciences at the University of Notre, Notre Dame, Indiana (USA). He is a public health engineer interested in the transmission of human pathogens via environmental and engineered systems. His work includes the use of environmental microbiology techniques to detect and quantify rare pathogens, quantitative microbial risk assessment to estimate risks to human health, and BioRender to create compelling scientific illustrations.
Dr. Warish Ahmed is a senior research scientist in the Industry and Environments research program in CSIRO Land & Water, Brisbane (Australia). He provides solutions to identify sources of microbial contaminants in water resources. His primary research areas are identifying the microbial composition/biodiversity of aquatic ecosystems and surveillance of dangerous pathogens in sand/sediment, wastewater, and environmental water sources.
About this blog section
The section #FascinatingMicrobes for the #FEMSmicroBlog explains the science behind a paper and highlights the significance and broader context of a recent finding. One of the main goals is to share the fascinating spectrum of microbes across all fields of microbiology.
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