Airports are integral to connecting towns, cities, and even countries—but in addition to shuttling passengers and cargo, they can also contribute to the spread of infectious pathogens like SARS-CoV-2, making them a strategic location for pathogen surveillance. Airport-based PCR testing can identify positive cases to potentially limit SARS-CoV-2 transmission. In normal PCR-based SARS-CoV-2 screening at airports, arriving passengers are required to undergo swab testing, which determines whether they will be allowed to enter the country at all, whether they must quarantine on arrival, or something similar. A portion of the swab samples collected from arriving passengers is usually submitted for full-genome sequencing to monitor the emergence of new variants as well, guiding worldwide public health efforts. However, collecting and processing thousands of individual swab samples can be logistically challenging, especially on an ongoing basis. Environmental surveillance provides a potential solution for this problem, and Agrawal et al.’s recent paper1 shows us how well this can work with detection of the Omicron variant by airport wastewater surveillance.
By collecting genetic material from SARS-CoV-2 particles found in the environment, particularly in wastewater, scientists can build an anonymized, non-invasive picture of the current state of the SARS-CoV-2 population in the area from whence that water comes. This can be repeated to track changes over time. Viral loads and variant composition can be monitored in specific populations by collecting samples at wastewater treatment plants or from wastewater streams with known origins. This method is already in use around the world to provide a sense of the SARS-CoV-2 situation within cities. The European Centre for Disease Prevention and Control (eCDC) has been a proponent of wastewater surveillance, spearheading efforts to boost the wastewater surveillance network across 20 European countries. In response to emergence of the Omicron variant, the eCDC suggested that airports use wastewater surveillance with genomic sequencing to detect the introduction of Omicron from incoming flights. Airports provide an especially interesting application of wastewater surveillance, combining the advantages of this high-level surveillance method with the chance to discover new strains arriving from afar, and Agrawal et al. used this method to impressive effect at Frankfurt Airport in Germany.
Agrawal et al. monitored two wastewater streams: a canal receiving wastewater from Frankfurt Airport and an influent stream at a wastewater treatment plant in the city of Frankfurt. Composite 24-hour samples were collected on November 2nd and November 23rd. They performed genomic sequencing with the Ion AmpliSeq SARS-CoV-2 Research Panel on Ion GeneStudio S5 instruments. The first known detection of Omicron in the Frankfurt area was in their wastewater sample from Frankfurt Airport on November 23rd. No other wastewater samples from the city of Frankfurt showed Omicron, nor were cases of Omicron SARS-CoV-2 known in Frankfurt before this reading. Frankfurt’s first Omicron case from an individual sample was reported a few days later on the 29th, collected from an arriving passenger at Frankfurt Airport on the 26th. Omicron was therefore identified in wastewater samples prior to its detection from an individual swab. This is not the first time that wastewater surveillance has provided an early warning of the arrival of new variants. Such capacity is especially important at Frankfurt Airport, a major hub for connecting flights between various European destinations, North America, and Asia.
Airports continue to be one of the most common ways that SARS-CoV-2 variants arrive in new countries, and monitoring the movement of the virus at airports provides an advance window on what the virus population will look like in cities in the weeks that follow. Agrawal et al.’s study demonstrates the value of wastewater surveillance with genomic sequencing at transportation hubs like airports for early, comprehensive variant detection. Combined with ongoing swab-based testing, wastewater surveillance can provide a comprehensive picture of SARS-CoV-2 variants around the world, enabling researchers and public health officials to make informed decisions on mitigation measures to potentially reduce the spread of new and emerging variants.
For Research Use Only. Not for use in diagnostic procedures.
1. Agrawal S, L Orschler, S Tavazzi, et al. (n.d.). Genome Sequencing of Wastewater Confirms the Arrival of the SARS-CoV-2 Omicron Variant at Frankfurt Airport but Limited Spread in the City of Frankfurt, Germany, in November 2021. Microbiol. Resour. Announc. 11(2):e01229-21.