SARS-CoV-2 infection from contaminated water systems
COVID-19: SARS-CoV-2 infection from contaminated water systems. Jefferson T, Heneghan C.
Published on July 3, 2020
Transmission Dynamics of COVID-19
||Shutler J, Zaraska K, Holding TM, Machnik M, Uppuluri K, Ashton I, et al. Risk of SARS-CoV-2 infection from contaminated water systems. MedRxiv. https://doi.org/10.1101/2020.06.17.20133504 2020
|| Funding: European Union Marie Curie Innovative 205 Training Network AquaSense, Engineering and Physical Science Research Council (EPSRC), European Space Agency project Ocean SODA and the authors’ institutions
||Water flow, temperature
Based on data from 39 countries, SARS-CoV-2 can remain stable within water for up to 25 Days. Country-specific risk of infection posed by faecal contaminated water is environment-dependent, with water flow and temperature as important variables.
The authors designed a viral survivability curve based on what is known about viral properties.
They found that absolute viral concentrations are higher and will exist for longer within countries with a combination of higher relative risk, colder water and high population infection rates.
Countries with lowest relative risk of infection are those with both high domestic water usage and high dilution (eg Canada, Norway and Venezuela). Highest relative risk results from a combination of low to medium domestic water usage and low dilution (eg Morocco, Spain, Germany).
The authors conclude that viral concentrations reduce quickly in Morocco within 24 hours of a spill, but remain for longer in Spain and the UK where water temperatures are lower.
Source: Risk of SARS-CoV-2 infection from contaminated water systems. medRxiv. 2020:2020.06.17.20133504.
What did they do?
The study aimed at assessing the survivability of SARS-CoV-2 within water systems
on the basis of published in vitro study data and then carried out pollution analysis to calculate the dilution in rivers. Combined these data with a virus survivability model, the authors calculated the relative risk posed to humans by sewage spills in 39 countries. Using infection data as at 3 May 2020 for 21 countries in which inland water temperatures were available, the authors identified viable waterborne virus concentrations that would lead to high risk of infection if faecal contamination had occurred.
The authors applied these results to the proportion of the population infected within 21 countries on 3rd May 2020, assuming that a spill occurred, identifying the estimated upper and lower limit of viable waterborne virus concentration within the first 24 hours
The correlation is predicated on a mixture of available data and assumptions about water flow and rainfall. While the results appear plausible, the methods chapter is thin and countries with a high number of cases and deaths such as USA and Italy are not included^ (grey areas in the figure)
|Clearly defined setting
||Demographic characteristics described
||Follow-up length was sufficient
||Transmission outcomes assessed
||Main biases are taken into consideration
What else should I consider?
Although the correlation appears a relatively good fit with the incidence of cases and deaths, the gaps in the data set and the timing of the study mean that it requires replication.
About the authors
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, epidemiologist.