Wastewater-based epidemiology for COVID-19 monitoring and public health protection at three UK airports

In a recently published study by PLOS Global Public HealthResearchers tracked severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2) at UK airports using effluent monitoring.

Research: Wastewater-based monitoring of SARS-CoV-2 at UK airports and its potential role in international public health surveillance.  Image credit: Caron Badkin/Shutterstock
Research: Wastewater-based monitoring of SARS-CoV-2 at UK airports and its potential role in international public health surveillance. Image credit: Caron Badkin/Shutterstock

Background

Air travel plays a significant role in the spread of many enteric and respiratory infections around the world, including coronavirus disease 2019 (COVID-19). Although travel restrictions have been implemented worldwide, asymptomatic or pre-symptomatic carriers of SARS-CoV-2 may transmit the virus.

To estimate SARS-CoV-2 penetration rates across international borders, additional methodologies need to be developed as current clinical surveillance systems are still limited. One such method is wastewater-based epidemiology (WBE), which allows unbiased sampling of SARS-CoV-2 samples among groups of passengers entering airports.

Regarding the research

In the current study, the team studied sewage found in terminal and aircraft samples at three UK international airports over one to three weeks.

The team evaluated five sample concentration procedures on SARS-CoV-2-spiked samples and used the most effective approach for follow-up samples. As a process control, the SARS-CoV-2-spiked samples were split into three aliquot groups, further impregnated with phi6 bacteriophage. Along with each sample batch, positive and negative process controls were used to assess infection efficiency and recovery. Each sample underwent two preliminary treatments that included beef extract (BE)-sodium nitrate (NaNO3) and sodium chloride (NaCl) along with two concentration techniques that included ultrafiltration and polyethylene glycol (PEG) precipitation.

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One of the aliquot groups was concentrated with PEG precipitation as well as ultrafiltration without any prior treatment. The second set was combined with sodium chloride. The samples were centrifuged to separate solids from the supernatant, which were then soaked in PEG to form NaCl/PEG, followed by ultrafiltration to form NaCl/Amicon. In the third set, sodium nitrate and beef extract were combined. Centrifugation and PEG precipitation of the samples resulted in the formation of BE-NaNO3/PEG samples.

results

The BE-NaNO3/PEG precipitation approach demonstrated the highest virus recovery among the investigated procedures, for the SARS-CoV-2 N1 gene fragment as well as for the process control virus phi6. Also, a Shapiro-Wilk normality test revealed that the data distribution for phi6, SARS-CoV-2 and crAssphage strikingly deviated from normality. Kruskal Wallis rank sum test and Pairwise Wilcoxon tests showed that BE-NaNO3 technique was significantly superior for SARS-CoV-2 and phi6 and crAssphage recovery. Therefore, the follow-up samples were treated with BE-NaNO3 prior to PEG precipitation.

The control virus was detected in most samples; However, none of the vacuum truck samples from Heathrow Airport reported a viral presence. Recovery rates of vacuum truck samples at Heathrow and Bristol Central Terminal (CTA) sites were low. In several cases, SARS-CoV-2 and crAssphage were found in samples without Phi6 recovery, possibly as a result of low spike amounts.

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Most of the wastewater samples collected from the three airports contained crAssphage deoxyribonucleic acid (DNA) and SARS-CoV-2 ribonucleic acid (RNA). The Edinburgh International Terminal (JR)-1 samples showed the lowest SARS-CoV-2 levels and detection rates. The rest of the samples collected in Edinburgh tested positive for SARS-CoV-2, with the exception of one sample collected at a wastewater treatment plant (WWTP).

All samples collected at Edinburgh Airport reported high amounts of crAssphage. However, pumping station sites (P1), JR2, and JR3 showed significantly higher turbidity, ammonium levels, and electrical conductivity than WWTP and JR1 sites. No noteworthy trends in SARS-CoV-2 concentrations over time were noted at any of the sampled sites.

At Bristol and Heathrow airports, all sewage samples received from the terminals tested positive for SARS-CoV-2 and crAssphage. In these locations, the amounts of ammonium and turbidity in the samples were higher than those in the Edinburgh samples. The pH values ​​of samples obtained at the Bristol sites were also higher than at Heathrow and Edinburgh. Furthermore, no correlation was detected between viral levels and chemical data.

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The contents of vacuum trucks carrying aircraft sewage have also been tested for the presence of SARS-CoV-2. At Bristol and Edinburgh, all samples tested positive for SARS-CoV-2, while at Heathrow, all but two samples tested positive. Also, crAssphage was detected in all vacuum truck samples received from Bristol and Edinburgh airports and 40% of those received from Heathrow airport. In addition, the team found no relationship between detection rates or levels of SARS-CoV-2 and crAssphage. Also, the sample’s pH, orthophosphate levels, turbidity, and in some cases, electrical conductivity were significantly higher than those of the other samples.

Summary

The study findings showed that WBE may be used as an effective surveillance technique for SARS-CoV-2 and other viral infections in airports to locate international outbreak hotspots and assess trends in infection incidence. The study noted that even with highly efficient extraction techniques, aircraft sewage samples may contain solids and chemicals that reduce the likelihood of effective virus detection.

The researchers believe that regular sampling of aircraft and airport effluents can be used as a targeted surveillance method for new diseases and other agents that are not yet endemic to the country.

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