COVID-19 in sewage of the Mohawk and Hudson Rivers

A potential hazard for water quality studies

As the new reality evolves surrounding the Covid-19 pandemic of 2020, communities grapple with the complexity of isolation and continuity of essential services.  One of those essential services is wastewater and sewage treatment.  For those of us who have worked on water-quality issues prior to the pandemic, a critical question is what effect the Covid-19 virus is having on wastewater and water quality in the watershed. In short, it is clear that wastewater - both raw and treated - has distinct genetic markers for Covid-19 and that wastewater-based epidemiology may become a critical tool in the fight against the virus [9]. What is unclear is the critically important question as to whether transmission of the virus is possible from pathogens in surface waters contaminated by raw or treated sewage.

For some time now water-quality monitoring in the Mohawk watershed has been the focus of a number of scientists from NGOs, colleges, and universities, as well as state and federal agencies [see 2020 examples in ref 1].  Those monitoring efforts appear to have completely shut down due to the pandemic, largely because labs have closed.  It is possible that testing of the main stem of the Mohawk will be impaired for months – perhaps the entire season - because navigation on the Mohawk may not be possible due to closure of locks that are in need of repair [2].

In January 2020 it was demonstrated that the biomarkers of COVID-19 (SARS-CoV-2) were present in the waste of an infected patient from Snohomish County in Washington State [3]. Hence there was a concern that wastewater from positive patients could be an infection route. 

SARS outbreaks (SARS-CoV – similar to COVID-19) were generally attributed to large superspreading events, but one outbreak was traced to aerosolization of virus-contaminated sewage in an apartment complex in Hong Kong [4,5].  The role of fecal transmission has yet to be determined for COVID-19, but it seems likely given observations from the SARS outbreak [5]. 

Given potential issues with plumbing in some buildings and the experience with SARS, Michael Gromley and colleagues at Heriot-Watt University in Edinburgh wrote: “The potential for a substantial viral load within the wastewater plumbing system (and therefore the main sewer system), in combination with the potential for airborne transmission due to aerosolisation of the virus, calls for wastewater plumbing systems to be considered as a potential transmission pathway for COVID-19.” [5].

On 30 March 2020, Gertjan Medema at the KWR Water Research Institute in the Netherlands and colleagues released a non-peer-reviewed study [6] that showed that the virus could be detected in sewage from seven cities in the Netherlands.  Their data show the emergence of the virus in the population during initial infection. COVID-19 genetic markers were not detected in samples taken on 6 Feb 2020, but were detected in samples from six sites by mid-March of 2020.  They wrote:

“This is the first report of detection of SARS-CoV-2 in sewage. The detection of the virus in sewage, even when the COVID-19 prevalence is low, indicates that sewage surveillance could be a sensitive tool to monitor the circulation of the virus in the population.” [6]

They also note: ”There is no epidemiological signal or case reports in the Netherlands or other countries that are hit by the COVID-19 pandemic that sewage is a transmission route for SARS-CoV-2... Therefore, sewage does not seem to be a transmission pathway of significance for SARS-CoV-2”  [6]. They suggest that using RT-qPCR [explained in 7] identification techniques on wastewater has shown that quantification of the viral load is a leading indicator of infection in the population because the signal rose before significant numbers of cases were reported by health surveillance.  The same pattern was seen in Parisian wastewater [see 10], and probably in Massachusetts wastewater [15] but perhaps not in wastewater from Brisbane [17] .

On 7 April 2020, Wu and colleagues reported the first confirmed occurrence of COVID-19 in sewage in the in US. Ten samples taken between 18 and 25 March 2020 from an unnamed wastewater treatment facility in Massachusetts (likely in the Boston area) tested positive.  The viral titers (concentrations) measured in this study were higher that what would be predicted for the known/reported clinically diagnosed cases in this area.  This result may reflect the presence of asymptomatic cases or may indicate issues with model assumptions [15 - see also discussion of model issues in 17].

Smriti Mallapaty, a correspondent at Nature, summarized early emerging work on wastewater in early April 2020. She wrote on 9 April 2020 [8] that monitoring wastewater may be important in determining the viral load in communities, a finding that may become increasingly important because the number of asymptomatic cases appears to be significant. A key step in this work is to determine how much viral RNA is excreted from infected individuals and then to estimate how that material is transferred to wastewater. Wastewater monitoring could be used to evaluate the extent of current infection in a community or to provide early warning of outbreaks in the future.

Given the clear genetic markers, it is possible that wastewater-based epidemiology (WBE) could be used to monitor the progress of COVID-19, but there may be more rapid approaches to detection. Kang Mao at the Institute of Geochemistry, Chinese Academy of Sciences, Guiyang, China, and colleagues [9] suggest that: “Currently, the most direct method for the detection of SARS-CoV-2 is a nucleic acid−based polymerase chain reaction (PCR) assay…. the paper-based device has the potential to be used as a small, portable device to detect SARS-CoV-2 in wastewater on site and to track virus carriers in the community. Such an approach could provide near real-time and continuous data and serve as an early warning sensing system…” 

One of the most significant WBE studies to emerge is on wastewater in Paris. Wurtzer and colleagues submitted a preprint on 17 April titled “Time course quantitative detection of SARS-CoC-2 in Parisian waste waters correlates with COVID-19 confirmed cases.”  This paper, like many rapid submissions in the last 30 days, has not been peer-reviewed, and was submitted to MedRxiv on 17 April 2020 [10].  All raw (untreated) wastewater from Paris collected from 5 March to 7 April 2020 tested positive for SARS CoV2, and 75% (6 or 8) samples from treated wastewater were positive for the virus, but the treated sewage water showed a reduction in the viral load by a factor of 100. Two important points come for the Parisian study: 1) the number of genomic units in wastewater have a positive correlation to incidence of COVID-19 in the population; and 2) the virus can be detected in both raw and, to a lesser degree, in treated wastewater [10]. 

Figure 1 modified from Wurtzer et al study on COVID-19 in Parisian wastewater (submitted 17 April 2020) [10]. They detected SARS-CoV-2 genomic material in raw sewage and treated sewage (after wastewater treatment). Treated-sewage line (estimated and added here) does not include an outlier.

In an article by Kate Baggaley in Popular Science titled “Poop could be the key to tracking COVID-19 outbreaks” [11], she wrote that an email from Sebastien Wurtzer noted:  “Future studies will be needed to determine whether the virus is still capable of growing after passing through wastewater treatment plants. The team in Paris is currently investigating whether the viruses showing up in sewage are still infectious…” [11]

Thus over and over we see that a central WBE question is whether the virus is viable in wastewater. My reading of the literature would indicate that it may not be, but also that it is too early to tell.  Early experiments in Germany may indicate that it is not viable and therefore not transmissive from wastewater.  In a popular German podcast released on 25 March 2020, Prof. Christian Drosten, director of Institute of Virology at Charité – Universitätsmedizin Berlin, told co-host Korinna Henning that his group at the University hospital tried to culture cells in the lab but were unsuccessful.  Thus he notes that it doesn’t look as if the virus is infectious in this setting.  If this result has been published, I have not found it.  The transcript of the podcast can be found here (in German) [16].

On 23 April 2020 the World Health Organization (WHO) wrote:  “Currently, there are no studies on the survival of the COVID19 virus in drinking-water or sewage. The morphology and chemical structure of this virus are similar to those of other corona viruses for which there are data about both survival in the environment and effective inactivation measures” [13].  They imply that wastewater managers should consider final disinfection (chlorination) of treated wastewater if treatment plants are not optimized to remove viruses.

Given this background, there is obviously concern about testing in the Mohawk and Hudson watersheds, especially in surface waters potentially contaminated with sewage – raw or treated. After an initial pause, Riverkeeper has started patrols and testing in the Hudson. An important question has been whether it is safe to test water that may be sewage-contaminated.  

Note that there is probably little chance of exposure to the virus in clear natural surface waters, but the concern is in waters that may be impaired with sewage from communities where COVID-19 is widespread, and in the lower Hudson this would be New York City, the COVID-19 epicenter in the US.  Before the pandemic hit, considerable work had already gone into identifying rivers and streams in the Hudson watershed that are impaired by raw sewage, so the concern is not a new one, but the potential hazard of the virus is.  On 12 April 2020, Dan Shapley, Water Quality Program director at Riverkeeper, wrote:

“In the Hudson River Watershed, it is important to understand whether the infectious virus is present at concentrations that present a risk – particularly in waters affected by sewage effluent that lacks disinfection, combined sewer overflows, contaminated sediment, aerosols, or other sources….  While any potential exposure risk is likely to be substantially lower than for other modes of transmission (such as interpersonal contact), the available evidence suggests a potential risk of exposure to COVID-19 virus in sewage-contaminated water.” [12]

In the Mohawk watershed there is concern about human pathogens in surface waters at several levels.  One is the nature of the discharge from wastewater treatment plants, and another is impaired surface waters affected by raw sewage by either leaking pipes or combined sewer outfalls.  The latter issue has now become even more critical. Our work on a small urban stream in Schenectady [14] shows that raw sewage enters the stream - undoubtedly due to leaking sewage pipes - at both high- and low-flow conditions.  Thus there is the possibility that impaired streams like this one in urban settings may have a hazardous viral load and thus contact with these waters should proceed only with caution (and PPE). Certainly it seems prudent that these waters should be avoided for recreational contact.

---

This and other Notes from a Watershed are available at: https://mohawk.substack.com/

---

ADDED since initial post:

Watch a discussion about the science of testing sewage.

Andy Revkin hosted and interesting hour-long discussion about using sewage-based pathogen testing. This discussion was with Jeff Schlegelmilch, deputy director of Columbia’s National Center for Disaster Preparedness, Rolf Halden, Director of the Biodesign Center for Environmental Health Engineering at ASU, and Angie Rasmussen a virologist at the Center for infection and Immunity at Columbia University.  The discussion, entitled “COIVD-19 Innovations: The Sewage Solution to Tracking Pandemic Patterns” streamed on 23 April 2020 and can now be viewed on YouTube (here).

---

Further reading

[1] Garver, J.I., Smith, J.A., and Rodak, C. 2020. Proceedings of the 2020 Mohawk Watershed Symposium, Union College, Schenectady, NY, March 20, 2020, Volume 12, 74 pages (volume here).

[2] Carlin, Rick.  “Canal season is in limbo – With work halted it’s uncertain if locks will be ready for summer boating this year.”  Albany Times Union.  21 April 2020.

[3] Holshue, M. L.; DeBolt, C.; Lindquist, S.; Lofy, K. H.; Wiesman, J.; Bruce, H.; Spitters, C.; Ericson, K.; Wilkerson, S.; Tural, A.; Diaz, G.; Cohn, A.; Fox, L.; Patel, A.; Gerber, S. I.; Kim, L.; Tong, S.; Lu, X.; Lindstrom, S.; Pallansch, M. A.; Weldon, W. C.; Biggs, H. M.; Uyeki, T. M.; Pillai, S. K. First Case of 2019 Novel Coronavirus in the United States. N. Engl. J. Med. 2020, 382 (10), 929−936 (paper here). 

[4] Heymann, D.L. and Shindo, N., 2020. COVID-19: what is next for public health? The Lancet, 395(10224), pp.542-545. (paper here)

[5] Gormley, M., Aspray, T.J. and Kelly, D.A., 2020. COVID-19: mitigating transmission via wastewater plumbing systems. The Lancet Global Health (23 March 2020).  (Paper here)

[6] Medema, G., Heijnen, L., Elsinga, G., Italiaander, R. and Brouwer, A., 2020. Presence of SARS-Coronavirus-2 in sewage. medRxiv. (Preprint here)

[7] Quantitative reverse transcription PCR (RT-qPCR) is used when the starting material is RNA.  See explanation at ThermoFisher.

[8] Mallapaty, S., 2020. How sewage could reveal true scale of coronavirus outbreak. Nature, 580(7802), pp.176-177 (paper here).

[9] Mao, K., Zhang, H. and Yang, Z., 2020. Can a Paper-Based Device Trace COVID-19 Sources with Wastewater-Based Epidemiology? (paper here).

[10] Wurtzer, S., Marechal, V, Mouchel, JM, and Moulin, L., 2020.  Time course quantative detection of SARS-CoC-2 in Parisian wastewaters correlates with COVID-19 confirmed cases.  Not peer reviewed. Preprint submitted to MedRxiv on 17 April 2020.

[11] Kate Baggaley, 27 April 2020.  Poop could be the key to tracking COVID-19 outbreaks.  Popular Science. (article here).

[12] Shapley, Dan, Riverkeeper blog post.  04.12.20 “ Is COVID-19 virus present in water?” (Blog post here).

[13] World Health Organization, 2020. Water, sanitation, hygiene, and waste management for the COVID-19 virus: interim guidance, 23 April 2020 (No. WHO/2019-nCoV/IPC_WASH/2020.3). World Health Organization. (Guide here)

[14] Willard-Bauer, E., Smith, J.A., Garver, JI, Goldman, D., Newcomer, B., 2020.  Enterococci levels in the Hans Groot Kill and Mohawk River, Schenectady NY.  In Garver, J.I., Smith, J.A., and Rodak, C. 2020. Proceedings of the 2020 Mohawk Watershed Symposium, Union College, Schenectady, NY, March 20, 2020, Volume 12, p. 63-68 (abstract in this volume).

[15] Wu, F., Xiao, A., Zhang, J., Gu, X., Lee, W., Kauffman, K., Hanage, W., Matus, M., Ghaeli, N., Endo, N., Duvallet, C., Moniz, K., Erickson, T., Chai, P., Thompson, J., Alm, E., 2020. SARS-CoV-2 titers in wastewater are higher than expected from clinically confirmed cases Authors: (not peer reviewed) medRxiv. https://doi.org/10.1101/2020.04.05.20051540. (Paper here)

[16] Hennig, K. and C. Drosten (2020). Coronavirus Update. Folge 21 (transcript of the Podcast is here - in German).

[17] W. Ahmed, N. Angel, J. Edson, et al., 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, Science of the Total Environment (2020). (paper here)