The unprecedented reaction to the COVID-19 pandemic has included a remarkable response from the water science community in a race to fill knowledge gaps. The Source looks at some of the key issues.
Training and planning for disasters and major incidents is part of the water industry’s preparedness as an essential service. But the sector, as with the world at large, has been astonished at the way our modern mobile lives, in particular, fuelled an escalation of the COVID-19 pandemic to a global concern in just a matter of weeks. The extent and speed of the measures it has provoked have been extraordinary, and the water science community around the world has been playing its part in the response.
The water sector has human health at the heart of what it does and why it exists. So, this science community has been called upon to examine what the disease – and, more specifically, the SARS-CoV-2 virus responsible – means for the sector and those it serves. The pandemic has brought new opportunities, including the prospect of using wastewater monitoring as a tool in tracking outbreaks, covered in a separate article. But the rapid spread means there has been cause, virtually simultaneously, around the world to revisit even some of the basic aspects of what the sector does and how it operates.
Confidence in our baseline
The disease may be new, but the sector is already armed with a great deal of relevant knowledge, including knowledge based on the SARS epidemic of 2002-04. It is a baseline that appears relatively straightforward, but is important nonetheless. To start with, COVID-19 is, at least primarily, a viral respiratory disease mainly transmitted through droplets and respiratory secretions. That means transmission by coughing and sneezing, but also simply by talking, with direct airborne transmission, as well as indirect transmission by fomites – surfaces of any kind on which droplets may settle.
The word ‘coronavirus’ has now entered common use by the global population. One important virus feature is the lipid envelope that encases the virus RNA.
“We think it is good news that this virus has a lipid envelope. That means it should be less stable in the environment,” says Dr Rosina Girones, Professor of Microbiology at the Microbiology and Statistics Department, University of Barcelona, and a member of the IWA COVID-19 Task Force. She makes a comparison with, for example, the enteric viruses on which the water sector is normally focused.
This aspect about the normal focus of the water sector is another important part of the baseline, too. Viruses in water have been studied for more than 70 years, with important enteric viruses, including hepatitis A. Water source protection and management, and the treatment of drinking water – including residual chlorination – already take account of viruses. The safety of drinking water with respect to viruses is long-established, including for viruses transmitted by water, such as adenoviruses, enteroviruses and noroviruses.
It is for this reason that Dr Gertjan Medema, Principal Microbiologist at KWR Water Research Institute in The Netherlands, explains the advice that could be given early on in the pandemic to his country’s drinking water suppliers – and which they, in turn, could communicate to their customers. The treatment processes in use are “adequately inactivating or removing these viruses that are more robust than the SARS-CoV-2, so we can safely say that drinking water is safe against these pathogenic viruses, including this new coronavirus”, he says.
The faecal question
Set against this relative certainty are the many questions around the presence and significance of the SARS-CoV-2 virus in faeces. The virus is excreted in respiratory secretions by infected people for prolonged periods, but often for longer in faeces. Here, water sector scientists have been following the progress made by the medical community.
Medema has pioneered the early work on use of wastewater monitoring of the virus as a public health tool, based on polymerase chain reaction (PCR) methods that detect viral genetic targets in wastewater. This testing option emerged quickly using the information on gene sequences provided from China.
One of the critical goals of the science community is to determine whether or not the virus in faeces is infective. Current information, which is minimal, suggests that the virus loses its infectivity in faeces. However, more studies are needed. As this requires use of culture-based methods in secure (biosafety level 3) laboratories, the virus inactivation rates are taking much longer to establish.
“We see that the virus is detectable in sewage with RNA-based methods,” says Medema. This connects back to faecal stool samples in which, he says, the virus has been found “quite extensively” and “in relatively high concentrations”. He adds: “The reports on occurrence of infectious virus in the stool samples of this SARS-CoV-2 are mixed, so we take [from this] that it is difficult to find infectious virus in stool samples, and it indicates that live virus are not present in high concentrations there.”
Presence of infective virus in faeces would open the way for potential faecal-oral or faecal- pharyngeal transmission, and the potential spread through contamination of water sources.
“There has not been any proof of faecal-oral transmission,” says Girones, who adds that there has been increasing data showing the virus may multiply in the intestine, meaning the ingestion route needs further study.
In any case, potential spread by contamination of surfaces overlaps with the already clear risk posed by airborne sources contaminating surfaces. These converge with one of the other areas of clarity in the pandemic and the role of contaminated hands: that handwashing has a central role to play in reducing the rate of transmission, alongside the now widely practised social distancing measures.
One of the biggest immediate concerns for the sector has been around what risk its workforce faces. As has become clear for all sectors, work roles may present a risk of person-to-person transmission. Utilities have had to comply with government calls for homeworking and protective measures, such as social distancing, while at the same time ensuring continuity of essential water services.
Many of the further questions for the water sector around COVID-19 stem from a need to understand the significance of the virus in faeces. For wastewater operators in particular, this has prompted the question of whether further occupational safety measures are needed, in addition to the more general person-to-person measures.
Medema sums up the general situation in this respect: “For the current pandemic, there is no epidemiological signal emerging in any of the countries that are experiencing the epidemic that sewer workers and sewage treatment plant workers are at special risk from this virus.”
This complements the position before the pandemic that most epidemiological studies do not reveal excess risk for wastewater treatment plant workers around the world in terms of gastrointestinal illness, or even respiratory illness, when – importantly – proper safety measures are in place. This means when good personal protection is used – which, for such workers, includes gloves, eye protection, masks, and handwashing.
The main concern is likely to be from exposure to bioaerosols of sewage released to the atmosphere. The time for which droplets of different sizes remain airborne, and how far they travel, is a whole other area of study, both for exhaled droplets – as in sneezing or speaking – and aerosolised liquids. The significance of this depends also on the survival of the virus. There is general confidence building as more information is discussed on the survival of this virus, and the control of viruses in general in wastewater, despite the gaps and concerns about the severity of the disease regarding SARS-CoV-2.
“The closer you get to the headworks in the [wastewater treatment] plant itself, and to areas where you have the potential for aerosolisation, I think would be areas of greater concern,” says Professor Chuck Haas, LD Betz Professor of Environmental Engineering at Drexel University. This means areas such as bar screens or wet wells. But he adds: “The risk is low, although yet to be quantified, and standard PPE that wastewater operators should be wearing ought to be effective to reduce that risk further.”
The clear evidence that the virus is arriving at wastewater treatment plants has prompted a need to understand whether there is any cause for concern about subsequent release to the environment.
“It is important to distinguish between detection of RNA virus target and detection of viable SARS-CoV-2 virus,” says Haas. “There are only a few reports of detection of viable virus at levels that might be significant for risk in excreta, and none in sewage. However, viral RNA has been detected, and if, in fact, that represents the potential for viable virions to be there, it is important for risk assessment.”
Medema explains that his work looking at wastewater monitoring has involved taking some final effluent samples after treatment at activated sludge plants. “So far, those have been negative, which is good news,” he says.
Knowledge gaps remain, but wider experience does offer a guide. For example, Haas says that work done elsewhere demonstrates greater removal of other enveloped viruses by secondary treatment compared with enteroviruses. “We would expect, particularly in activated sludge, to have a fairly high level of removal,” he adds. A high level of degradation of SARS-CoV-2 would also be expected because of the RNA-ase enzymes that degrade RNA in biological treatment, he adds.
Studies on surface inactivation, including work making comparisons with SARS, also indicate that chemical disinfection should be effective. Haas says that studies have shown SARS-CoV-2 is more sensitive than SARS to various chemical surface disinfectants, including bleach, indicating that there should be a “reasonably high” sensitivity to chlorine-based disinfection, as well as ozone and peracetic acid.
“The persistence of SARS-CoV-2, and amenability to chemical inactivation, is similar to that of SARS, which, in turn, is more sensitive than other viruses we encounter in the water sector,” Haas adds. “So, certainly, treatment either on the wastewater side or the drinking water side is expected to deal with the problem.”
Filling the knowledge gaps
There has been cause for confidence from a water perspective, essentially because of the likely and relatively lower significance of SARS-CoV-2 compared with the many other viruses the sector already has to consider. But this does not suggest there is room for complacency.
During the SARS epidemic of 2002-04, faulty operation of the sanitary system in a high-rise building in Hong Kong was found to be the cause of transmission between residences by aerosols. Hospitals and healthcare facilities are another natural focus of interest, given that any concerns around potential transmission from wastewater will be accentuated here, alongside a higher need for hygiene.
“Transmission could be possible in very highly contaminated environments,” says Medema, mentioning the Hong Kong example and hospital sewers. “But in terms of how likely it is that it is spread through the urban water cycle, I think the likelihood is pretty low.”
There are further knowledge gaps, including some that may be unintended consequences of measures brought in by governments in response to the pandemic.
For example, as communities start to emerge from lockdown, commercial and industrial buildings, and facilities such as cooling towers, will need to be brought back into service. “We need to pay a lot of attention to how these are brought back into service, so that we don’t have other concerns in terms of what the building plumbing has been growing during periods of stagnation,” says Haas.
Haas also notes that there has been a move in some locations to use hotels for the isolation and quarantine of either suspected or confirmed cases of COVID-19, and that these premises may not be set up to handle infectious waste in the same way that hospitals are. “I would want to keep an eye on those potential hotels that have not been set up for infectious waste, to be sure that we have a handle on what is happening there,” he says.
The race around risk
Much of the science work that is needed is, ultimately, about filling gaps around all the factors that contribute to the risk of transmission of COVID-19.
Substantial work is needed to answer fundamental questions such as the connection between the dose of virus received by inhalation and infection. Given the time involved for this, sources such as animal data from SARS have to be used.
This has to be combined with an understanding of how the virus can persist and remain viable, which depends on having a reliable cell culture method. Even with one, a full picture only comes after looking at a whole range of variables – including basic ones such as temperature, let alone the complex conditions in a wastewater treatment plant – and understanding, for example, any tendency of the virus to adhere to particles. Again, other sources need to suffice in the meantime, such as information from the study of human and feline coronaviruses, and how these compare with other viruses, such as polio virus.
Given that the characteristics of SARS-CoV-2 include having a lipid envelope, there are basic expectations about it degrading in the aquatic environment – that the virus will begin to degrade in a matter of a few hours, but may be persistent for a few days, quite possibly longer.
Professor Joan Rose is Homer Nowlin Chair in Water Research at Michigan State University and chairs the IWA COVID-19 Task Force. She sums up the overall picture: “We already know there are hundreds of enteric viruses in wastewater, and we have studied these and their removal. The further away we get from faeces, from raw water and sewers, and move into treated wastewater and rivers, we think it is going to be less likely that these envelope viruses can be transmitted very far in surface or groundwaters, and persist or then pass through the food chain.”
But, she adds, that the monitoring data is only just now emerging. Despite the strong grounds for anticipating that SARS-CoV-2 represents less of a risk in the water context compared with other viruses, the prominence and prevalence of COVID-19 means it is expected that reassurance will be sought around, for example, irrigation with used water, other reuse options, the reuse of sewage sludge, and recreational waters.
“We have some understanding about how to prevent exposure,” says Rose, who notes that quantitative data are needed – and are starting to appear – to confirm aspects such as inactivation rates and, with it, the wider picture on risk.
“We believe that risk is orders and orders of magnitude lower than the viruses that we normally would deal with in wastewater systems.”
Looking ahead, Rose notes in particular the very positive contribution the water science community is seeking to make, including developing and exploring further the potential use of wastewater monitoring for assessing COVID-19 in the community and supporting public health action (see separate article).
“There certainly is an urgency and desire for the water industry and environmental virologists to continue work on the wider water science aspects of COVID-19,” she says.
Rose believes use of a risk framework provides an approach to place the COVID-19 work into existing science approaches, including occurrence, concentrations, viability, persistence and removal by treatment processes. “By examining viral transport and fate, a robust foundation has been laid,” she says.
Viability and inactivation rates are some of the most significant gaps that Rose sees need to be addressed soon. It will also be important to keep vigilant in the monitoring of any outbreaks, to provide lessons learned on what may have gone wrong and the role of any transmission outside of the respiratory route.
“I have been very privileged to be part of the water industry and health-related water microbiology science communities,” says Rose. “This global response has been simultaneous and rapid, and, via our networks, we are learning more each day that will allow us to respond to this crisis and any new threats in the future.”
Information resources on water and COVID-19 – iwa-network.org/news/information-resources-on-water-and-covid-19
‘COVID-19: A Water Professional’s Perspective’, iwa-network.org/learn/covid-19-a-water-professionals-perspective, held 8 April 2020
Article based on input from the IWA COVID-19 Task Force and comments made during online discussion ‘COVID-19: A Water Professional’s Perspective’, iwa-network.org/learn/covid-19-a-water-professionals-perspective, held 8 April 2020. Additional reporting by Keith Hayward
Filling the wastewater risk assessment gap
One of the early tasks of the IWA COVID-19 Task Force has been to prepare an authoritative paper reviewing potential issues and concerns around the SARS-CoV-2 virus and connections with sewage treatment.
The water sector is used to thinking about viruses, both in relation to water supply and sanitation. This is why, for example, there is a high degree of confidence that the virus does not present a threat in treated drinking water supplies. SARS-CoV-2 does, though, have its own specific characteristics. Sewage treatment represents a focal point for the sector in terms of where knowledge gaps need to be filled.
The aim of the Task Force paper is to provide needed guidance to support risk mitigation based on currently available knowledge of viruses in wastewater.
Viral material is found in sewage, but this does not mean that infectious virus particles are present. More scientific research is needed to fill gaps in relation to SARS-CoV-2, such as any risk of faecal-oral transmission, the survival of the virus in sewage and other human waste streams of faecal origin, and the potential for transmission by aerosols.
Against this backdrop, it is nonetheless important that appropriate control measures are in place for wastewater treatment processes. The Task Force paper aims to present an overview of existing evidence-based research regarding the relationship between COVID-19 and wastewater, and of appropriate control measures that could be used for disease transmission mitigation.
The Task Force has, therefore, reviewed the science around SARS-CoV-2 in human faecal waste and untreated sewage. It has reviewed the effects of wastewater treatment and, so, its role in controlling the spread of the virus. This has involved looking at primary and secondary treatment, and at tertiary treatment and disinfection.
An important feature of the Task Force is that it brings together representatives of 10 of the most relevant Specialist Groups of IWA. It is also able to draw on input from the supporting Science Team convened by the Task Force. Given this, the paper also reviews other key aspects, including wastewater sludge, the reuse of water from treated effluents, and specific points relating to small wastewater treatment plants, as well as presenting a perspective in relation to developing country contexts.
Details of the paper’s publication will be available at iwa-connect.org/group/iwa-covid-19-task-force