We conclude our cycle of interviews on how sewage surveillance to track the spread of SARS-CoV-2, the virus responsible for COVID-19, has developed this past year around the world by talking to Dr Zhugen Yang, Lecturer in Sensor Technology at Cranfield University. We also had the pleasure of speaking to him last April on Cranfield’s paper device technology they had just launched.
Question: What is the current status of environmental surveillance for SARS-CoV-2?
Answer: In the COVID-19 pandemic, wastewater surveillance, as known as wastewater-based epidemiology (WBE) has mainly been used for SARS-CoV-2 detection in wastewater to realize environmental surveillance for SARS-CoV-2. Currently, SARS-CoV-2 RNA fragments have been detected in wastewater and sludge samples from many countries in the world including Australia, France, the Netherlands, Italy, the United States and Spain. Some studies have shown a good correlation between the concentration of SARS-CoV-2 RNA in wastewater and clinical case reports of COVID-19. The local and national monitoring programme has been funded, for example on university campuses, in schools and national monitoring programmes in the UK, the Netherlands and Australia. These all show a great promise for environmental surveillance.
Q: Could you explain what are the difficulties involved?
A: However, there are still challenges in terms of sampling, transportation of samples (cold storage), long turnaround time, and samples analysis and data interpretation.
Each sampling site faces specific and logistic challenges, including access, personnel health and safety, sample variability, and the possibility of clogging. Particularly, virus particles are usually unevenly distributed in the environment, so the differences between samples are usually large.
There are still challenges in terms of sampling, transportation of samples (cold storage), long turnaround time, and samples analysis and data interpretation
Currently, reverse transcription quantitative polymerise chain reaction (rt-qPCR) is the gold-standard method. It needs a sample concentration for sewage before running RT-qPCR analysis. Although a variety of protocol has been used for sample concentration experiments, there is no standard method. Multiple experiments are needed to test the robustness of the concentration method. Moreover, the presence of certain chemical substances and biosolids can inhibit the PCR process, thereby differentially inhibiting the recovery efficiency of viral RNA and gene amplification. The matrix type of the sample will affect the detected genetic signal intensity (genetic copy number), and the environmental samples usually have a greater impact on signal intensity than the clinical samples. Sometimes, the uncertainties (e.g. diluted concentration due to rainfall) make difficulties for both detection and interpretation even more difficulties in the following:
Temperature, microbial activity and chemical substances will affect the rate of RNA degradation. Unsuitable sample transport, storage, handling and preparation will accelerate the rate of RNA degradation, which results in the underestimation of virus quantification in environmental samples. Currently, we do not fully understand the fate of viruses in environmental samples, including how virus particles are broken down, or how any free RNA behaves when transported in water.
Uncertainties, such as diluted concentration due to rainfall, make problems with both detection and interpretation even more difficult. In some resource-limited regions, the sewage infrastructure is poor, which may cause the virus to be directly discharged into the surface water and interfere with sampling and analysis. Therefore, it is necessary to further understand the environmental dynamics, persistence and spread of SARS-CoV-2 to promote environmental surveillance for SARS-CoV-2.
Q: What do you see as future research directions in this area?
A: Analytical method can be improved to save cost and time and data interpretation. For example, low-cost and rapid sewage sensors (e.g. paper-based sensors) may play an increasing role in this surveillance, which will enable immediate decision making for early warning.
Sampling, transportation, concentration, extraction and detection methods need to be improved, control and quality standards need to be formulated. The analytical performance (e.g. sensitivity and specificity) are an indispensable part of environmental surveillance for SARS-CoV-2. Researchers from different laboratories (cross-validation) are required to make concerted efforts to standardize and coordinate experimental methods and strategies. This will need to combine multidisciplinary and cross-subject expertise.
It is necessary to further understand the environmental dynamics, persistence and spread of SARS-CoV-2 to promote environmental surveillance for SARS-CoV-2
Environmental surveillance for SARS-CoV-2 will be used to discuss virus transmission trend, transmission trend changes and community infection evaluation. Various experiments are necessary to analyze the shedding rate and duration of SARS-CoV-2, the relationship between the SARS-CoV-2 genetic signal and the infection prevalence, and the specific impact of the environmental matrix on the SARS-CoV-2.
Low-cost, portable and rapid sampling, concentration, extraction and testing kits need to be developed for on-site testing, especially in the resource-limited regions. These areas lack advanced laboratories, sufficient equipment and experienced researchers, it may not be possible to use common laboratory-based methods to realize environmental surveillance for SARS-CoV-2.
Q: Can you comment on the success of efforts to implement SARS-CoV-2 monitoring in wastewater in support of public health responses?
A: It’s very positive to see that this method has been rapidly rolled out in different regions and countries, including both developed and developing areas. Though we are facing lots of challenges, especially during the pandemic, the facilities and reagents may be constrains, as well as logistical issue for sampling. As mentioned, many sectors of countries are very active to support this surveillance programme from both researches to pilot level. I think the key is that wastewater monitoring is beneficial as an early warning of pandemics. Studies have shown that an increase in SARS-CoV-2 RNA can be detected in environmental samples a few days before the clinical detection. This is of significant importance for people who have no or mild symptoms. Wastewater monitoring may also be used to detect the unrecognised spread of SARS-CoV-2 and to determine whether COVID-19 is contained in an area, which can help to inform adjustments to social measures to improve public health.
Wastewater surveillance can also be used to assess the spread of COVID-19 infection among populations in resource-poor areas
Q: To what extent do you think wastewater surveillance can contribute to disease prevention and control during the remainder of this pandemic and any future ones?
A: Wastewater surveillance serves as an early warning of COVID-19 outbreaks in the population of a specific sewage collection community, and can reflect the infection rate, infection trend and changes in the infection trend at the population level, which is beneficial for the government to formulate epidemic prevention policies and protect public health. Wastewater surveillance can also be used to assess the spread of COVID-19 infection among populations in resource-poor areas. In addition, genetic sequencing of viruses can indicate the presence of SARS-CoV-2. In principle, this approach can also be used for other infectious diseases by detecting the genetic biomarkers of disease for early warning. In the future, with the progress of technology, it can be used as a routine monitoring method to inform public health. In particular, in resource-limited regions, insufficient medical resources will result in low clinical testing capabilities, so wastewater monitoring can be an effective and economic way for monitoring infections in the community.