The source and fate of pandemic viruses in the urban water cycle

This paper was produced by Dr Krista Rule Wigginton, Associate Professor in the Department of Civil and Environmental Engineering at the University of Michigan and two students under her supervision (Y. Ye and R.M. Ellenberg). It was commissioned by the Editors of the Royal Society of Chemistry journal “Environmental Science: Water Research & Technology” as part of their “Emerging Investigator” series.

The paper provides a thorough review of a number of important viral outbreaks, with much of the emphasis on coronaviruses (SARS and MERS), from the perspective of drinking water and wastewater management. Among the key findings are:

  • In general, these enveloped viruses are not considered a major threat for the wastewater and water industries due to their assumed low concentrations in municipal wastewater and high susceptibilities to degradation in aqueous environments.
  • A number of clinical reports, however, suggest that certain enveloped viruses are excreted in human faeces during infection. Furthermore, survivability studies show that many enveloped viruses are capable of retaining infectivity for days to months in aqueous environments.

The authors conclude that there remain a number of important research questions that must be answered “before the water and wastewater industries can confidently assure the public, through the dissemination of evidence-based guidance, that irrigation waters, recreation waters, and drinking water sources are safe during a viral outbreak or pandemic event”.

A number of important observations are made regarding coronaviruses and their potential presence in the urban water cycle (references to support these statements are provided in the paper):

Presence in excreted material (faeces and urine)

During one cluster of cases at an apartment complex in Hong Kong, the [SARS] outbreak spread via aerosolized faecal particles in the air ducts of the apartment complex. SARS-CoV RNA was often detected in the faeces of infected individuals, with the detection frequencies in different cohorts ranging from 16% to 97%.

MERS-CoV RNA was detected at low levels in the stool and urine of one infected individual, but absent in stool samples from two other infected individuals. Likewise, human coronavirus (HKU1-CoV) RNA has also been detected in stool samples.

Survival in untreated municipal wastewater

SARS-CoV has a T90 value of 9 days in culture media at room temperature. Inactivation rates are highly dependent on the water temperature and matrix. Higher temperatures are associated with higher inactivation rates, as is increased salinity.

In two studies of human coronaviruses in water, temperature was found to have the most pronounced effect of a range of variables on survivability, with up to an order of magnitude difference in decay rates between samples at 4 °C and room temperature.

The water composition, such as the presence of proteins or microorganisms, also influences virus survivability. Viruses in sterilized wastewater, for example, are inactivated at different rates than viruses in non-sterilized wastewater.

The presence of suspended solids and organic material increased the survivability of enteric viruses in aqueous environments. Likewise, coronaviruses survived longer in unfiltered primary effluent than in filtered primary effluent.

Wastewater treatment

The authors state that to their knowledge, there are no reports on the fate of enveloped viruses through wastewater treatment trains. Information is given regarding the fate of non-enveloped human viruses, indicating that removal and inactivation depends on the type of virus and on the treatment processes employed at a particular treatment plant.

Drinking water treatment

The authors state that more experiments are needed on enveloped viruses in water quality engineering processes before major conclusions can be drawn on their fate in wastewater and drinking water treatment. In general, enveloped viruses are more susceptible to common drinking water disinfectants than non-enveloped viruses. However, SARS-CoV was reported to be relatively persistent in experiments with UV disinfection.

Detecting enveloped viruses in water

The authors provide an overview of the available and emerging methods for detection of enveloped viruses in water matrices. However, they state that research on enveloped virus presence and fate in water is currently hindered by the lack of proven detection methods.

Conclusions

The overarching conclusion of this review is that “major knowledge gaps exist on the potential role of the urban water cycle in the spread of enveloped viruses, particularly for avian influenza viruses and coronaviruses”.

The authors propose a number of areas needing further research. Among others, these include:

  • Development of suitable (and validated) analytical methods for detection in water matrices
  • Presence and fate of enveloped viruses during wastewater and drinking water treatment processes
  • Quantitative risk assessments for highly pathogenic enveloped viruses in wastewater, recreational waters, and drinking waters.

Notably, the authors state that “it is quite plausible that a highly virulent new coronavirus like SARS-CoV will emerge in the future and pose challenges for the water and wastewater industries”.

Reference:

Wigginton KR, Ye Y and Ellenberg RM (2015) Emerging investigators series: the source and fate of pandemic viruses in the urban water cycle. Environmental Science: Water Research & Technology, 1(6), 735-746.

https://doi.org/10.1039/C5EW00125K

Published by Stuart Khan

Professor of Civil & Environmental Engineering, University of New South Wales

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