Is Coronavirus Spreading in Sewage? Effective Treatment in Municipal Wastewater and Septic Systems.
When a new human disease emerges and demonstrates a rapid and widespread distribution across international borders, it is important to investigate all possible exposure and transmission scenarios. The ongoing COVID-19 outbreak is overwhelmingly a respiratory disease transmitted by air and surface contact. However, previous, related disease outbreaks were shown to include cases of the virus being transmitted by sewage. This article presents what is currently known about the spread via contaminated sewage of the novel coronavirus that causes COVID-19, and the destruction of the virus during municipal or septic wastewater treatment.
One thing is certain: wash your hands, thoroughly and often, and keep your distance from other people.
Disclaimer: The information presented here summarizes current knowledge about a rapidly evolving viral pandemic. For the most current official information, visit Health Canada, the World Health Organization, the Centers for Disease Control, and other reputable information sources.
If you’re a data junkie, the Center for Systems Science & Engineering at Johns Hopkins University is maintaining a global map of the pandemic.
A New COVID-19 Transmission Worry?
Though it started quietly, with early signs of a new disease outbreak in China, the insidious expansion of COVID-19 to a global pandemic has put it at the forefront of public discussion. Daily admonitions from public officials and the media to wash our hands, sneeze into our elbows and practice “social distancing,” is inescapable. COVID-19 is a respiratory disease transmitted mainly through airborne and personal contact.
The virus that causes COVID-19 is also highly infectious and there been limited reports indicating the possibility of its transmission through sewage. Good public health policy demands that with any outbreak of a new disease, every potential avenue by which the disease can spread is studied and understood.
As of Mid-March, 2020, Canada has over 400 reported cases, putting it at about the middle of the pack for countries globally. The Public Health Agency of Canada, as of mid-March, states that the risk for the general public in Canada from COVID-19 is low, but there is an elevated risk for the elderly, those with compromised immune systems and those with underlying health issues.
A Coronavirus Disease Primer
“Coronavirus” and “COVID-19” have been used somewhat interchangeably in the general media since the outbreak was first reported in January of 2020, so it’s useful to know the difference between the two.
Coronaviruses are a large family of related viruses that infect humans and animals. Like other types of virus, human coronaviruses only infect humans, pig coronaviruses only infect pigs, bird coronaviruses only birds, and so on. But, when conditions are right, these viruses can, rarely, but sometimes, “jump species” and infect humans. The new human coronavirus creating havoc around the world is called “severe acute respiratory syndrome coronavirus 2” or SARS-CoV-2.
Current but unconfirmed research is suggesting that SARS-CoV-2 originated in pangolins, an anteater-like animal used in some Chinese medicines, before jumping species to humans. Earlier studies had suggested bats to be the source, but scientists have found a 99% genetic match between pangolin coronavirus and human SARS-CoV-2. That’s pretty compelling evidence.
COVID-19 is the name given by the World Health Organization to the human disease caused by SARS-CoV-2.
COVID-19 appears with flu-like symptoms, including fever and a dry cough, and in severe cases develops into pneumonia that can be fatal. Symptoms can take up to 14 days after exposure to appear, and some individuals may be infected with no visible symptoms.
As with other coronaviruses, SARS-CoV-2 is a respiratory pathogen that is transmitted from person to person by breathing airborne viral particles or by hand-to-mouth contact after touching virus-contaminated surfaces such as railings, door handles, light switches and the like.
When the general term coronavirus is used, it is to draw on the knowledge and experience gained from dealing with other coronavirus epidemics of the past, such as the SARS disease outbreak that originated in China in the early 2000s and the MERS disease outbreak in the Middle East around 2013.
These outbreaks are significantly informing government and public health officials in their assessment and handling of the current COVID-19 situation, including best practices for controlling its spread and the treatment of those who become ill.
The SARS and MERS coronavirus outbreaks are also relevant to our discussion of sewage and wastewater concerns during the COVID-19 disease outbreak because they provide evidence of the likelihood of the disease being spread through contaminated wastewater and sewage.
Coronavirus Transmission Through Plumbing is Possible – But Not Likely a To Be a Significant Source of Infections
The concern about possible transmission of the COVID-19 virus through sewage arose in the area of China where the disease outbreak started. Two elderly persons in the Tsing Yi area of Wuhan fell ill with COVID-19 but had no known contact with each other.
They did, however, live in the same apartment building, though their apartments were 10 floors apart, and this prompted officials to investigate. They found that bathroom plumbing had been altered in one of the victims’ apartments, which left an unsealed pipe and an open path for transmission of airborne sewage droplets – and potentially of coronavirus – through the building’s ventilation system.
Though certainly not definitive proof – the victims may just as likely visited and became infected in a location that was not the apartment building – the situation did highlight the need to explore this potential viral transmission route.
In fact, a study of the SARS outbreak in 2003 found transmission of that coronavirus from sewage did occur in some cases in Hong Kong. In large apartment buildings there, bathrooms included floor drains outfitted with standard U-traps and connected to the main wastewater stack.
However, the floor drains were seldom used, so the U-traps were dry, meaning there was no water barrier between the waste stack and the building’s bathrooms. Negative pressure from the bathrooms’ exhaust fans was sufficient to draw virus-contaminated sewage aerosols from the waste stack into the bathroom, where it could be inhaled. The spread of SARS throughout these buildings was attributed to this route of exposure.
This reveals that even standard plumbing installations could allow a pathway aerosolized sewage, containing virus particles, back into living spaces, where it can be inhaled and cause infection.
Faecal Transmission of COIVD-19: But Isn’t this a Respiratory Disease?
Of course, COVID-19, like SARS, MERS and the common cold or flu, is a respiratory disease. It is not transmitted orally, through drinking contaminated water or eating contaminated food.
The main exposure is through airborne contact, as when an infected person coughs or sneezes, releasing virus particles into the air, which other persons may then breathe and become infected. Personal contact, from shaking hands or hugging, is also highly likely to transmit the virus from person to person.
COVID-19 can also survive on surfaces for two to three days, as when a sick person coughs into their hand and then touches a doorknob, for example, or sneezes without covering and airborne viral particles then settle onto surfaces. Anyone touching those contaminated surfaces picks up virus particles on their hands, and if they then touch their face, infection is highly likely to occur.
Further troubling is that some infected individuals may be asymptomatic – not visibly sick or feeling unwell – and still be spreading the virus in these ways.
Many diseases that affect the stomach and bowels, like cholera and dysentery, are spread through unintentional contamination of drinking water supplies with sewage or wastewater carrying the faeces of infected individuals. The concern with coronavirus is not through this route of transmission, but rather from exposure to wastewater or sewage aerosols through which they might breathe in viral particles. This was verified during the SARS outbreak and is being actively investigated in the Tsing Yi incident.
There is evidence that in some small number of COVID-19 cases, patients experience nausea, vomiting and diarrhoea, indicating that the stomach and bowels are affected by the virus. This may even be an early warning sign of COVID-19 infection. It’s also notable that the related SARS virus was found to be present in the faeces of infected individuals, and that the virus could survive in untreated sewage for up to 8 days.
So, even though COVID-19 is primarily a respiratory disease that spreads through airborne and surface contact, the virus particles that cause it can end up in the waste stream from the faeces of infected individuals.
Coronavirus Down the Drain: Worry?
It’s reasonable to ask, what happens to the virus with all the hand washing that we are doing? Are we just washing virus down the drain and into the waste stream, and is thus magnifying the exposure risk? What if you’re sick and self-isolating at home, what happens with virus-contaminated wastewater from the toilet or sink or shower? And is soap better than hand sanitizer?
Coronaviruses are tiny packages of RNA (a chemical relative of DNA), coated with lipids and proteins. Soap and warm water do a good job of breaking apart the viral package so that it’s no longer infectious – it’s just a collection of biological molecules that get washed down the drain. (If soap isn’t available, hand sanitizer that is at least 60% alcohol also breaks apart the virus.)
As we’ve seen, the virus that causes COVID-19 has been detected in the faeces of some infected individuals, meaning that in general, a portion of the infected population is excreting virus when using the toilet. So, the presence of COVID-19 coronavirus in wastewater is expected, though not from showering or hand-washing.
CDC and EPA: Wastewater Treatment is Effective Against COVID-19 Coronavirus
Fortunately, the US Centers for Disease Control and Environmental Protection Agency make clear that properly functioning and maintained municipal wastewater treatment and private septic systems will effectively eliminate the virus. The COVID-19 coronavirus is particularly susceptible to disinfection, so municipal systems that maintain proper chlorination levels during routine treatment operations are eliminating the virus from the waste stream.
Remember, routine wipe-downs of surfaces with a bleach solution is an important part of COVID-19 prevention. Think of municipal treatment as “wiping down” the wastewater with bleach. Also keep in mind that public drinking water supplies are disinfected prior to distribution, and with the virus being highly susceptible to disinfection, it is highly improbable to survive routine treatment practices.
Septic tanks do not disinfect, but a properly sited (i.e., away from drinking water supplies) and functioning septic system will effectively treat the virus as it does other household pathogens, through the normal biological and chemical processes that occur in the tank and leaching field. The EPA does recommend that those with private wells, who are concerned about adequate isolation of their well from the septic system, consider home filtration devices. Anything under 30 meters between the septic system and well can be considered more at risk.
COVID-19 coronavirus has not been detected in drinking water. (Phew!) In general, the CDC considers the risk of transmission of the virus through sewerage systems to below, and the World Health Organization has found no evidence of sewage transmission of the COVID-19 virus (with the Tsing Yi incident being under investigation).
Sewage: An Early Warning System for Viral Outbreaks
As far as COVID-19 is concerned, it may be that we’ve dodged a bullet because sewage is not a major form of virus transmission. While the risk is low, COVID-19 coronavirus is present in faeces of infected individuals, and it is plausible that it could be transmitted in sewage under certain conditions, as is suspected in Tsing Yi, so vigilance is important.
It’s also important to keep in mind that there is a long list of nasty, virulent pathogens transmitted in sewage. In fact, some researchers have been doing some really interesting work in testing sewage to predict disease outbreaks.
As we continue to deal with the ongoing coronavirus situation, be sure that efforts are being made to learn from the present situation, to be more effective in our response to the next, inevitable outbreak.
Wrap-Up: Best Practices for Staying Safe
There are simple and straightforward things to know and practices to follow in the interest of staying safe during the current COVID-19 pandemic. They have been presented and discussed daily on a variety of media platforms, and merit repeating here:
- The COVID-19 coronavirus is a highly infectious respiratory disease.
- The virus is mainly spread through the air when infected individuals cough or sneeze, from close contact with infected individuals, and from touching contaminated surfaces.
- Infected individuals may not experience symptoms of illness and not know that they are sick, but they can still transmit the virus.
- A vaccine or other treatment against the COVID-19 coronavirus is not currently available, and will not be for many months.
Prevention of COVID-19:
- Avoid crowds as much as possible.
- Cough or sneeze into your elbow.
- Wash hands thoroughly (20 seconds, front and back, under fingernails) and often, with soap. Hand sanitizer is effective when soap and water are unavailable.
- Don’t touch your face, to reduce the chance of transferring the virus from your hands.
- Wipe high-touch surfaces (doorknobs, switches, railings, TV remotes, phones, other electronics) with a bleach solution (9 parts water: 1 part bleach).
- Common face masks will not protect you from the virus; if you are sick a mask may help minimize the chance of you spreading the virus.
- If you don’t feel well, stay at home and avoid contact with other people.
May you be well and stay well!
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