By Sally Brown, University of Washington
Abstracts of these resources are available in the searchable Information Portal offered to Northwest Biosolids members.
- CoVID-19: faecal–oral transmission?
- Virological assessment of hospitalized patients with COVID-2019
- Presence of SARS-Coronavirus-2 in sewage
- SARS-CoV-2 titers in wastewater are higher than expected from clinically confirmed cases
- Can a paper-based device trace COVID-19 sources with wastewater-based epidemiology?
I promise that the next library will be something light and entertaining. Biosolids based soil blends perhaps or how biosolids can save the world. Right now, my obsession, one likely shared by many of you, is still on this virus. Every day I check for the daily case counts in King County and Washington State (gradually decreasing I am happy to report). We are all still stuck at home and all still concerned about our own health and safety. And, as residual professionals- still wondering how waste and wastewater plays into this. The first library I did on the virus was about corona viruses in general. Now there is some information out there on this virus specifically. So here is what we know.
First article – this is primarily a respiratory virus. But not totally a respiratory virus. Diarrhea is one of the lesser reported symptoms. The article – a short summary of findings, points out that gastrointestinal symptoms are present to varying degrees. More importantly they note that rectal swabs or samples of fecal material can test positive for the virus. They refer to a number of cases where fecal samples continued to test positive even after nasal swabs were negative. In other words, fecal oral route of transmission is viable with COVID- 19. Yet another reason to wash your hands. The second article details progression in 9 patients in Germany who had relatively mild cases of the virus. Sampling began as symptoms presented. The authors took repeated swabs and samples from the throat, spit and as fecal samples. The virus was present in high number in the throat in initial sampling. They did not find live virus in the stools. They conclude that respiratory spread is the big concern here but note that they had a limited sample size and that only one of the patients that they sampled had diarrhea. So not a clear result but indications that fecal transmission is possible if not common. Also important here is that the virus can be detected in fecal material. That is the introduction to the next three articles. These articles focus on detection of the virus in wastewater.
We’ve seen articles before where the authors suggest that wastewater can be used as a window onto society. For example, testing wastewater for illegal drugs has been suggested as a way to determine how widespread drug use is in a community. It can also be used as a way to measure the presence of disease in a community – termed wastewater-based epidemiology (WBE). These next three articles focus on whether wastewater can be used to detect how widespread the COVID-19 virus is in communities. No work yet on viability of the virus or how long viable copies of this particular virus persist in wastewater- Ian Pepper is likely hard at work as I write. Even so- this is still of interest.
The third article comes from the Netherlands. The authors used RT- PCR to look for fragments of the actual protein as well as for the envelope. They looked in wastewater from 7 cities as well as from the airport. That is one big airport and that was back in the day when planes were still flying. They found no samples on February 6th, three weeks prior to the first positive case in the Netherlands (February 27th). By March 5th, they detected they found portions of the virus in 5 of the sampled sites. By the 15th of March, that had increased to 6 sites with other portions of the virus also detected. The authors suggest that monitoring wastewater is a potential means to monitor for the presence of the virus in communities.
The fourth article does just that in Boston. The authors refer to previous work where WBE has been used to track disease spread in different communities. They collected wastewater from the central plant in Boston, using influent samples collected before anyone had ever heard of COVID-19 as a control. The used RT-qPCR to test for fragments of the virus- remember here this is a technique to study the presence of portions of the virus, not viability of those fragments. There were no hits from samples collected before the first known US case of the virus. However, all 10 samples collected from March 18-25th tested positive. They do a fascinating calculation to back track the detection in wastewater to estimate the number of people infected:
‘Nonetheless, we can estimate an abundance based on the lowest observed values across these samples of ~10 copies/mL. If we assume typical stool sizes of 200g, diluted into an average volume of 1.36*109 L, and a population of 2.3*106 individuals each producing one stool per day, and we further assume that there is no loss of viral RNA in sewer lines and that excreted viruses are fully suspended in sewage, then we expect the viral titer in feces to be about 3000 times higher than that in sampled raw sewage, or about 30,000 particles per mL.’
In order to really get this right, they would need to understand how much virus shows up in the poop and if that number changes over the course of infection. They noted that one study found as many as 600,000 viral genomes in each mL of poop. By their estimates, about 5% of Boston was infected- much higher than the 0.026% of cases in MA confirmed using tests. If instead they used a higher rate of viral genomes in the poop- they get an estimate of 0.1% positive- much closer to the reported rate of infection. If we have a good idea of quantity of virus in fecal material- this could be a really powerful tool to test for outbreaks. Talk about source control.
The final paper in the library talks about the potential to use a simpler test to detect the virus in wastewater. That would really make this an excellent tool. They have a list of different diseases that have been detectable using rapid, easy systems in wastewater. Rotavirus A uses a special piece of paper and the naked eye to get a positive. Others like human papillomavirus use specially developed papers and smart phones. Conclusions here are that we wastewater types may be part of a solution to contain the virus. That sounds pretty sweet to my ears.