Coronavirus Found in Wastewaters: What Does it Mean for the Pandemic
Coronavirus Found in Wastewaters: What Does it Mean for the Pandemic

And how wastewater-based epidemiology (WBE) prevents potential outbreaks.

Image by Sebastian Ganso from Pixabay

The novel coronavirus, SARS-CoV-2, causes gastrointestinal symptoms, such as diarrhea, nausea, and abdominal pain, about 10% of the time. The reason is that SARS-CoV-2 can infect gastrointestinal cells that express high levels of ACE2 receptor. It makes sense that SARS-CoV-2 would shed through the feces as well, which is true. As follows, the next question is: Might wastewaters be a source of Covid-19 transmission?

Persistent and infectious SARS-CoV-2 in feces

The prevalence of fecal shedding of SARS-CoV-2 in clinical settings is about 50–80%, according to a research review of Masaaki Kitajima, an assistant professor specializing in water microbiology at the University of Tokyo.

A few studies have detected infectious, active SARS-CoV-2 in fecal samples that are culturable (the act of infecting cells with viruses) in the lab. One study, however, failed to culture SARS-CoV-2 isolated from feces of Covid-19 patients, which implies inactive viruses. Nonetheless, a negative finding does not negate other studies that have found infectious SARS-CoV-2 in feces.

Feces could be a persistent source of infectious SARS-CoV-2. Concerns have, thus, been raised about the possible fecal-to-oral spread of SARS-CoV-2.

SARS-CoV-2 can even be found in the feces of Covid-19 patients for 4–11 days after their nasopharyngeal swabs turned negative about 60% of the time. This might be due to the longer persistence of SARS-CoV-2 in the gastrointestinal system than the respiratory tract (mean of 27.9 vs. 16·7 days after symptom onset).

Therefore, the evidence suggests that feces could be a persistent source of infectious SARS-CoV-2. Concerns have, thus, been raised about the possible fecal-to-oral spread of SARS-CoV-2. For instance, contaminated feces from Covid-19 patients might enter wastewaters or sewage plants and end up in water supplies.

SARS-CoV-2 in wastewaters: Infectious or not?

Scientists have previously detected the genetic material of coronaviruses that cause common cold in wastewaters in the US and Saudi Arabia. A 2005 published study has also found persistent SARS coronavirus RNA in untreated and disinfected wastewaters from Beijing hospitals. Researchers believed this waterborne SARS might have contributed to the outbreak in areas with defective plumbing systems.

Since prior coronaviruses can be present in wastewaters, the chances are that SARS-CoV-2 can as well. Indeed, investigators in multiple countries have discovered SARS-CoV-2 genes in wastewaters (mostly untreated samples) in the Netherlands, USA (Massachusetts, Montana, and Louisiana), Germany, France, Turkey, Japan, Italy, Spain, and Australia.

“Conventional wastewater treatment processes should inactivate SARS-CoV-2, and multiple barriers used in drinking water treatment plants should suffice to remove SARS-CoV-2 to levels of non-detect and low risks.”

Importantly, the presence of viral genes does not prove viability or infectivity. So, scientists do not know if SARS-CoV-2 in wastewaters is infectious or not, owing to the constraints of current research tools. The stability of genomes in wastewaters is highly variable, which complicates the isolation of viruses for culturing (the act of infecting cells with viruses) in labs.

What the WHO says: Significance of the viral envelope

“While the presence of SARS-CoV-2 in untreated drinking water is possible, infectious virus has not been detected in drinking-water supplies,” states a July report by the World Health Organization (WHO).

The main reason is that SARS-CoV-2 is an enveloped virus, which is arguable its biggest weakness. An enveloped virus is less durable than non-enveloped viruses: The viral envelope is made up of fat, which is easily pulled apart by alcohol, soap, or disinfectants; in return, enveloped viruses readily infect mammalian cells whose cell membrane is also fat-based.

“SARS-CoV-2 is enveloped and thus less stable in the environment compared to non-enveloped human enteric viruses with known waterborne transmission (such as adenoviruses, norovirus, rotavirus, and hepatitis A virus),” the WHO report added. The proper treatment of wastewaters or sewage plants would result in a 99.9% reduction of coronaviruses of all sorts, the WHO claims.

“While the presence of SARS-CoV-2 in untreated drinking water is possible, infectious virus has not been detected in drinking-water supplies.”

Basically, the enveloped SARS-CoV-2 is vulnerable to environmental stressors such as changes in heat or pH. Thus, the waterborne spread of SARS-CoV-2 in properly treated water supplies is unlikely. “Conventional wastewater treatment processes should inactivate SARS-CoV-2, and multiple barriers used in drinking water treatment plants should suffice to remove SARS-CoV-2 to levels of non-detect and low risks,” Prof. Kitajima and others concurred.

But note that countries with poor wastewater treatment and sanitization infrastructures, such as Pakistan and India, may face an increased risk of waterborne spread of SARS-CoV-2.

Value of wastewater-based epidemiology (WBE)

Even if wastewaters SARS-CoV-2 may not be much of a concern in countries with access to clean water, the data still helps epidemiologists paint a clearer picture of the pandemic and potential outbreaks.

One perk of WBE is that it acts as a pool testing, where traces of viruses can be detected in groups of populations. “Detection in community wastewater of one symptomatic/asymptomatic infected case per 100 to 2,000,000 non-infected people is theoretically feasible, with some practical successes now being reported from around the world,” said Prof. Rolf U. Halden, a director of the Center for Environmental Health Engineering at the Biodesign Institute in Arizona.

For instance, the University of Arizona tested for the presence of SARS-CoV-2 in wastewater samples from each dorm, and one sample came back positive. The university then tested 311 students residing in that dorm and successfully quarantined two asymptomatic carriers of Covid-19 before any outbreaks.

“Wastewater surveillance could, therefore, be used to detect SARS-CoV-2 in the community and provide an estimate of the total number of infections. The added value is that this approach accounts for those who have not been tested, as they have no or mild symptoms,” agreed Anthony D. Harries, a senior advisor at the International Union against Tuberculosis and Lung Disease and an honorary professor at the London School of Hygiene and Tropical Medicine in the UK. “If lockdown measures have worked and a community is declared coronavirus free, routine wastewater surveillance could be used as an early warning alert that new infections are present.”

Even if wastewaters SARS-CoV-2 may not be much of a concern in countries with access to clean water, the data still helps epidemiologists paint a clearer picture of the pandemic and potential outbreaks.

WBE can also help compensate for the shortages and sub-par quality of diagnostic tests. This can save millions to billions of USD, as estimated by a statistical study of Prof. Halden. “WBE surveillance of populations is shown to be orders of magnitude cheaper and faster than clinical screening, yet cannot fully replace it,” the study concluded. “For resource-poor regions and nations, WBE may represent the only viable means of effective surveillance.”

Short Abstract

There have been confirmed cases of fecal shedding of infectious SARS-CoV-2 in Covid-19 patients. This had lead to the positive detection of SARS-CoV-2 in wastewaters around the world, which raised concerns for a possible fecal-to-oral route of transmission. Fortunately, SARS-CoV-2 is an enveloped virus that is susceptible to inactivation by standard wastewater treatment protocols. But this might not apply to countries that lack access to clean water. Regardless, there is value in wastewater-based epidemiology (WBE), where it offers a cost-effective means of pool testing, and the monitoring of current pandemic and potential outbreaks.
['Shin Jie Yong']
['Technology', 'Innovation', 'Life', 'Covid 19', 'Science']