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Q: How many days can SARS-CoV-2  survive in sewage water?

Krishna: I myself am interested in this question. Because one of our tenants recently died of Covid-19. When their family vacated the house, we had to clean the house and I was particularly worried about the toilets this person used in his last days. So I searched for information on this. I am giving below some of it.

1. Survival of Coronaviruses in Water and Wastewater

https://www.ncbi.nlm.nih.gov/pmc/articles/PMC7091381/

The abstract of this paper says: The advent of severe acute respiratory syndrome and its potential environmental transmission indicates the need for more information on the survival of coronavirus in water and wastewater. The survival of representative coronaviruses, feline infectious peritonitis virus, and human coronavirus 229E was determined in filtered and unfiltered tap water (4 and 23°C) and wastewater (23°C). This was compared to poliovirus 1 under the same test conditions. Inactivation of coronaviruses in the test water was highly dependent on temperature, level of organic matter, and presence of antagonistic bacteria. The time required for the virus titer to decrease 99.9% (T99.9) shows that in tap water, coronaviruses are inactivated faster in water at 23°C (10 days) than in water at 4°C (>100 days). Coronaviruses die off rapidly in wastewater, with T99.9 values of between 2 and 4 days. Poliovirus survived longer than coronaviruses in all test waters, except the 4°C tap water.

The main thing that determines the survival of virus is temperature.

At room temperature it required only 10 days to result in a 99.9% reduction of coronavirus in filtered tap water, while at 4°C ( you have that temperature in fridge and cooler water in India) this level of virus inactivation would require over 100 days.

The presence of organic matter and suspended solids in water can provide protection for viruses that adsorb to these particles but at the same time can be a mechanism for removal of viruses if the solids settle out. The level of organic matter and suspended solids in the test waters increased from tap water to secondary effluent to primary effluent. Coronavirus inactivation was greater in filtered tap water than unfiltered tap water.  This suggests that higher solids do provide protection for coronaviruses in water. 

The titer of the coronaviruses immediately decreased 99.9% upon addition to the wastewater. This decrease may be due to the presence of solvents and detergents in wastewater that would compromise the viral envelope and ultimately inactivate the virus.

The presence of predatory microorganisms, such as protozoa, can increase the inactivation rate of virus in water, as well as the action of proteases and nucleases .

Solids-associated viruses in wastewater are protected from predation and inactivation. However, the coronaviruses were below the minimum detection limit after 3 days.

Conclusion: The results of this study indicate that coronaviruses are  more sensitive to temperature . This may be due in part to the fact that enveloped viruses are less stable in the environment than nonenveloped viruses. Coronaviruses die off very rapidly in wastewater, with a 99.9% reduction in 2–3 days, which is comparable to the data on SARS-CoV survival. Survival of the coronaviruses in primary wastewater was only slightly longer than secondary wastewater, probably due to the higher level of suspended solids that offer protection from inactivation.  This study demonstrates that the transmission of coronaviruses would be less than enteroviruses in the aqueous environment due to the fact that coronaviruses are more rapidly inactivated in water and wastewater at ambient temperatures.

2. SARS-CoV-2 coronavirus in water and wastewater: A critical review about presence and concern

https://www.ncbi.nlm.nih.gov/pmc/articles/PMC7528884/

The abstract of this paper says: The presence of severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2) in water and wastewater has recently been reported. According to the updated literature, the stools and masks of the patients diagnosed with coronavirus disease (COVID-19) were considered as the primary route of coronavirus transmission into water and wastewater. Most coronavirus types which attack human (possible for SARS-CoV-2) are often inactivated rapidly in water (i.e., the survival of human coronavirus 229E in water being 7 day at 23 °C). However, the survival period of coronavirus in water environments strongly depends on temperature, property of water, concentration of suspended solids and organic matter, solution pH, and dose of disinfectant used. The World Health Organization has stated that the current disinfection process of drinking water could effectively inactivate most of the bacterial and viral communities present in water, especially SARS-CoV-2 (more sensitive to disinfectant like free chlorine). A recent study confirmed that SARS-CoV-2 RNA was detected in inflow wastewater (but not detected in outflow one). Although the existence of SARS-CoV-2 in water influents has been confirmed, an important question is whether it can survive or infect after the disinfection process of drinking water. To date, only one study confirmed that the infectivity of SARS-CoV-2 in water for people was null based on the absence of cytopathic effect (CPE) in infectivity tests. Therefore, further studies should focus on the survival of SARS-CoV-2 in water and wastewater under different operational conditions (i.e., temperature and water matrix) and whether the transmission from COVID-19-contaminated water to human is an emerging concern. Although paper-based devices have been suggested for detecting the traces of SARS-CoV-2 in water, the protocols and appropriate devices should be developed soon. Wastewater and sewage workers should follow the procedures for safety precaution against SARS-CoV-2 exposure.

For the coronavirus-infected communities living in apartment buildings, wastewater plumbing systems have been considered as a potential pathway for transmitting the SARS-CoV-1 coronavirus into the sewer system since 2013 . Similar to SARS-CoV-1, the SARS-CoV-2 virus can be spread via aerosols or microscopic water droplets . In fact, researchers  reported that the SARS-CoV-2 and SARS-CoV-1 viruses share a similarity in their stability in aerosols and on surfaces. Depending on the inoculum shed, the viruses can remain viable and infectious on surfaces (up to a few days) and in aerosols (for hours). Similarly, researchers investigated the survival of SARS-CoV-2 in air, surface, and personal protective equipment of disease carriers and healthcare workers. They found that the samples collected from air outlet fans, door handles, sinks, and toilet bowls were positive, which confirms that SARS-CoV-2 can be transmitted through the stools of infected people. Furthermore, some researchers collected the high-touch surface samples of a quarantine room (23 sites) and found that the percentage of collected samples was positive for SARS-CoV-2 as follows: 70% (in the bedroom) > 50% (bathroom) > 33% (corridor). They also concluded that the most contaminated sites with the highest viral loads were identified at the inner walls of the toilet bowl and the sewer inlet of the room . Such a transmission pathway, through the sanitary (or wastewater) plumbing system, might be likely responsible for environmental contamination and spread of COVID-19 in the communities . Therefore, researchers recently provided several recommendations to ensure that transmission through the wastewater plumbing system is minimized. The figure below summarizes some valuable suggestions to avoid the risk of spreading the pathogen through wastewater plumbing system in the buildings.

So we locked the house and kept it vacant for about 40 days  as it 's  rainy season now in India. I think after 40 days it is safe again to use it in this part of the world. I myself have entered it first, and when I found it is okay to use it again I allowed others to enter. We cleaned it and it is ready to occupy safely now. 

But our tenant's family kept it a secret that he died of covid-19 which 's more dangerous. If we really know the truth, we can take precautions. I was suspecious from the beginning and took the precautions despite their secrecy. But when we came to know about it through some reliable sources, I scolded them for keeping it a secret.

Don't keep covid-19 infection a secret and endanger others' lives.

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