Sentinel surveillance of SARS-CoV-2 in wastewater anticipates the occurrence of COVID-19 cases.

Sentinel surveillance of SARS-CoV-2 in wastewater anticipates the occurrence of COVID-19 cases. Jefferson T, Heneghan C.

Published on July 13, 2020

Reference Chavarria-Miró G, Anfruns-Estrada E, Guix S, Paraira M, Galofré B, Sáanchez G, et al. Sentinel surveillance of SARS-CoV-2 in wastewater anticipates the occurrence of COVID-19 cases. medRxiv. 2020:2020.06.13.20129627. 2020
Study type
Country Spain
Setting Water/Sewage/Community
Funding Details REVEAL project, funded by SUEZ Spain
Transmission mode Orofecal, waterborne
Exposures Wastewater

Bottom Line

SARS-CoV-2 was detected in sewage 41 days before the declaration of the first COVID-19 case in Spain and in frozen samples dating back to 12 March 2019. If confirmed, the results suggest SARS CoV-2 has been around longer than first thought.

Evidence Summary

The copies or antigenic concentration closely resembled the shape of the epidemic curve apart from a break possibly due to dilution secondary to heavy rainfall. SARS-CoV-2 was detected in sewage 41 days (January 15th) before the reporting of the first COVID-19 case (February 25th), making wastewater surveillance a possible method to forecast cases of a disease with agents excreted in stools.

Because most COVID-19 cases present with ILI and because there had been hypothesized cases before the index case, the researchers analysed frozen WWTP2 samples and found one positive, dating from 12th March 2019, some 10 months before the index case appearance. 

This suggested the presence of SARS-CoV-2 long before its appearance as a virulent infection. Of note is that earlier samples from January 2018 to January 2019 were negative for viral genome antigens.

What did they do?

The study reports the testing of 24-hour composite raw sewage samples from two large wastewater treatment plants (called WWTP1 and WWTP2) which were analysed weekly for the presence of SARS-CoV-2 in the periods from April 13th (the peak of the epidemic) to May 25th.  

Additionally, WWTP2 archived frozen samples were also analysed for the periods from 2018 (January-March), 2019 (January, March, September-December) and 2020 (January-March). The researchers used RT PCR to look for 5 different viral antigens.

Study reliability

The results of this study are potentially very important but need replicating, although similar studies included in the review showed similar results. In particular, the PCR testing technique could have produced false positives, although the researchers report following the FDA testing protocol^. It is also improbable that some of the viral material was infectious, so the results of this study should not be interpreted as proof of orofecal transmission.

Clearly defined setting Demographic characteristics described Follow-up length was sufficient Transmission outcomes assessed Main biases are taken into consideration
Yes No Yes Partly Partly

What else should I consider?

The results of the study need replicating in other locations and the samples re-testing using different techniques.

About the authors

Carl Heneghan

Carl is Professor of EBM & Director of CEBM at the University of Oxford. He is also a GP and tweets @carlheneghan. He has an active interest in discovering the truth behind health research findings

Tom Jefferson

Tom Jefferson, epidemiologist.