In a recent study published in PLOS Global Public Healthresearchers conducted surveillance for severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2) at UK airports using sewage monitoring.
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 limitations have been put into practice around the world, asymptomatic or pre-symptomatic carriers of SARS-CoV-2 can transmit the virus.
To assess SARS-CoV-2 infiltration 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 for unbiased sampling of SARS-CoV-2 samples among groups of passengers entering airports.
About the study
In the current study, the team explored wastewater found in terminal and aircraft samples at three international airports in the UK for one to three weeks.
The team evaluated five sample concentration procedures on samples spiked with SARS-CoV-2 and used the most efficient approach on surveillance samples. As a process control, the SARS-CoV-2 spiked samples were split into three sets of aliquots, further spiked with bacteriophage phi6. With each batch of samples, positive and negative process controls were also used to assess cross-contamination and recovery efficiency. Each sample was subjected to two pretreatments involving beef extract (BE)-sodium nitrate (NaNO3) and sodium chloride (NaCl) as well as two concentration techniques involving ultrafiltration and polyethylene glycol precipitation ( PEG).
One of the aliquot sets was concentrated with PEG precipitation as well as ultrafiltration without any pretreatment. The second set was combined with sodium chloride. Samples were centrifuged to separate solids from supernatant, which were then PEG precipitated 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.
The BE-NaNO3/PEG knockdown approach demonstrated the highest viral recovery among the procedures studied, for the SARS-CoV-2 N1 gene fragment as well as for the phi6 process control virus. Additionally, a Shapiro-Wilk normality test revealed that the distribution of data for phi6, SARS-CoV-2, and crAssphage deviated remarkably from normality. A Kruskal Wallis rank sum test and pairwise Wilcoxon tests showed that the BE-NaNO3 technique was significantly superior for the recovery of SARS-CoV-2 and phi6 and crAsphage. Therefore, monitoring samples were treated with BE-NaNO3 before PEG precipitation.
Control virus was detected in the majority of samples; however, none of the vacuum truck samples from Heathrow Airport reported viral presence. Sample recovery rates from vacuum trucks at the Bristol and Heathrow Central Terminal Area (CTA) sites were low. In a few cases, SARS-CoV-2 and crAssphage were found in samples without Phi6 recovery, possibly due to low amounts of doping.
Most of the sewage samples collected at the three airports contained crAssphage deoxyribonucleic acid (DNA) and SARS-CoV-2 ribonucleic acid (RNA). Samples from International Terminal (JR)-1 at Edinburgh Airport showed the lowest levels and detection rates of SARS-CoV-2. The remaining samples collected in Edinburgh tested positive for SARS-CoV-2, except for one sample collected at the Wastewater Treatment Plant (WWTP).
All samples taken at Edinburgh Airport reported elevated amounts of crAssphage. However, the pump stations (P1), sites JR2 and JR3 had much higher turbidity, ammonium levels and electrical conductivity than sites WWTP and JR1. No remarkable trends were noted in SARS-CoV-2 concentrations over time at any of the sites sampled.
At Bristol and Heathrow airports, all sewage samples taken from the terminals tested positive for SARS-CoV-2 and crAssphage. At these locations, the amounts of ammonium and turbidity in the specimens 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. Additionally, no link was identified between viral levels and chemical data.
The contents of vacuum trucks carrying aircraft wastewater were also examined 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. Additionally, crAssphage was identified in all vacuum truck samples obtained from Bristol and Edinburgh airports and 40% of those obtained from Heathrow airport. Additionally, the team found no link between detection rates or levels of SARS-CoV-2 and crAssphage. Additionally, sample pH, orthophosphate levels, turbidity, and in some cases electrical conductivity were significantly higher than the other samples.
The study results showed that WBE could be used as an effective surveillance technique for SARS-CoV-2 and other viral infections at airports to locate outbreak hotspots internationally and to assess trends in the prevalence of infections. The study noted that even with extremely efficient extraction techniques, aircraft wastewater samples could contain solids and chemicals that decrease the likelihood of effective virus detection.
The researchers believe that regular sampling of aircraft and airport wastewater can serve as a targeted surveillance method for new diseases and other agents that are not yet endemic in the country.
. epidemiology based on water for surveillance COVID19 protection public health in three UK airports