By Sally Brown, University of Washington
Abstracts of these resources are available in the searchable Information Portal offered to Northwest Biosolids members.
Shedding of SARS-CoV-2 in feces and urine and its potential role in person-to-person transmission and the environment-based spread of COVID-19
Presence and infectivity of SARS-CoV-2 virus in wastewaters and rivers
Residuals and biosolids issues concerning COVID-19 virus
SARS-CoV-2 RNA in wastewater anticipated COVID-19 occurrence in a low prevalence area
First confirmed detection of SARS-CoV-2 in untreated wastewater in Australia: A proof of concept for the wastewater surveillance of COVID- 19 in the community
We are now at the end of August and Covid-19 has not gone away. What has changed? I for one, have a vastly expanded mask wardrobe. Solids, prints, causes; I have masks that fit into each category. While we have a long way to go to make this virus history, we do now have a better understanding of its behavior in human wastes and the facilities that treat them. I did two libraries on Covid-19 in April and figured that it was time for an update. The good news is that there is even more evidence that fecal transmission is not a major pathway and that wastewater treatment and its products are not a real concern for transmission. There is also good news in that work on wastewater-based epidemiology (WBE) – finding disease through wastewater sampling and analysis - has shown that this technique can track Covid-19. If you’ve had enough about Covid-19 you can stop reading here. Feel free to email me about my favorite masks.
If you want more information about Covid-19 and wastewater, let me take you through this library. The first article starts with a VERY detailed review on potential presence of the virus in the intestinal tract and in urine and feces. There is stuff that we know here- it is primarily a respiratory infection with a minority showing GI symptoms. You can also learn about ACE-2 receptor sites in the intestines and potential for viral replication. One pathway leading to fecal contamination with the virus is swallowing snot:
‘If sputum is swallowed, viral particles enveloped in mucus may pass down the GI tract in a semi-protected state and avoid degradation by gastric acid and bile/pancreatic juices (Hirose et al., 2017).'
But this is the critical quote from this part of the paper:
In a subsequent, more comprehensive study of COVID-19 cases, it was found that of the 153 stool specimens analyzed, 29% tested positive for SARS-CoV-2, from which infectious virus was recovered from 2 samples (Wang et al., 2020c).
In other words, even if virus is detected in feces (very uncommon to detect it in urine), it will be ineffective for the vast majority of cases. As the authors say: ’evidence suggests that feces and urine probably contain low levels to no infectious particles’. They go through a calculation of the likely dilution of genetic copies (gc) of the virus from a single person household. Starting with a viral load of 8 x 106 gc ml in feces you end up with effluent from that house with a maximum concentration of 5.9 x 107 gc/l- a very small portion of which, if any, will be infectious. From there you enter the sewer pipe and if you think that the environment there is friendly to a lone surviving viable virus copy- either ask Art Carney or think again.
The authors note that any remaining particles in the treatment plant are likely to partition to the solids (that’s us folks!) where regulations for biosolids stabilization will take care of business. They also note that within the treatment plant bioaerosols from secondary aeration would be the only area of risk and that the likelihood of an infectious dose here is very, very small.
They discuss any potential for risk to water bodies receiving treated effluent- (there isn’t any) and point out that the greater risk would be an infected individual swimming and spitting into the water. A very dense paper with more information that you can absorb- but there it is in print, wastewater is OK.
If that doesn’t convince you go to the second paper. This one presents research conducted in Milan, Italy. We aren’t allowed to go to Milan or anywhere else in Europe at the moment, so maybe this can be like a vicarious trip for you. Going to see the Last Supper by Da Vinci is on many lists of must dos in Milan.
Instead, we will look at article 2 in the library to see what happens as the guests from that supper digest their meals. Northern Italy was hit hard and early with Covid-19. The authors sampled influent into three treatment plants as well as effluent from those plants during the peak of the spread in that region. The water at the plants comes from a population of 2 million. All plants have secondary treatment with effluent undergoing tertiary treatment by peracetic acid or UV light. The authors used real time PCR to detect the virus. They also tested for viability of the virus. Finally, they sequenced the virus to see if in fact, what they detected was the same strain as what was prevalent in the area. When sampling freshwaters receiving effluent, they also tested for caffeine, as in indicator of untreated wastewater from CSOs. They found genes from the virus from all sampled plants on the first date (April 14th) but from only one of the plants the following week. They found NO virus in the treated wastewater on either date. They also found NO infective virus in either the influent or the effluent for either date. The authors estimate that the travel time from the source of the influent to the plant to be between 6-8 hours. Temperature of the influent was 18.5-19º C. They did find the virus in receiving water bodies on the first date, but only one of the rivers on the 2nd. They also found higher concentrations of caffeine in the rivers, suggesting a potential for some direct discharge of untreated wastewater. In one case they found some ineffective RNA without the caffeine and note that the sampled river also receives discharges from other plants that do not use tertiary treatment. What they detected was not infective and at a concentration well below an infective dose.
The third paper is another review of the issue, coming from the US. The lead author and heavy lifter here was Kari Fitzmorris Brisolara from Louisiana State University School of Public Health. Other authors include familiar names and trusted figures such as Bob Bastian (now retired) and Chuck Gerba (hopefully will never retire). This is an easier to read version of Paper #1 with more of a focus on wastewater and biosolids. It was written in April so does not have the more recent references, but it does have this great figure:
(EPA 1999; CDC 2008; Gattie & Lewis, 2004; Image: CDC Public Health Image Library https://phil.cdc.gov/Default.aspx)
The figure shows that corona viruses, of which Covid-19 is one, are relatively easily destroyed.
Hopefully the first part of this write up has gotten you excited about wearing masks and calmed you down about the virus in wastewater, effluent and biosolids. From here we turn the focus to WBE. For this virus it appears that publications recognize that we are now part of the team fighting against it, rather than one of the bad guys.
We continue with our virtual travel on the 4th paper, this time to Spain (where they are having a very big resurgence of the virus). The researchers focused on a region in Spain where no cases had been reported (Murcia). They used real time PCR and sampled both influent, secondary and tertiary effluent samples from March 12 to April 14th. They found hits in influent (only 2 hits from secondary and none from tertiary). These were compared with known cases on a municipal level. The WBE found the Covid before the municipal testing did. The authors point out that this type of WBE could be a very useful compliment to municipal testing programs.
The final paper takes us down under, to Brisbane. Again, the authors sampled influent and found Covid- 19. They used the concentrations to estimate prevalence of the virus in the community coming up with a median range of infected individuals of between 171 and 1090- or spanning an order of magnitude. This estimate was in general agreement with clinical observations. Further proof that WBE is a useful tool for Covid-19 and likely many other diseases.
So mask up and help join the good fight.