Alicia L. Johnson, “The Benefits and Risks of Monitoring Airport Wastewater" (Houston: Rice University’s Baker Institute for Public Policy, December 14, 2023), https://doi.org/10.25613/WGMW-PP67.
Nearly one billion travelers pass through U.S. airports each year. The holiday season often sees an increase in air travel and unfortunately, illness. To combat outbreaks, the Centers for Disease Control and Prevention (CDC) recently announced the expansion of its Traveler-based Genomic Surveillance (TGS) program to include RSV, the flu, SARS-CoV-2, and other pathogens.
Surveillance of infectious disease outbreaks and new variants is vital to public health. However, the current program has privacy concerns that should be addressed before being implemented more broadly — both at the airport and community levels.
The main goal of the TGS program is to act as an early-detection system to track genetic variants of pathogens entering the U.S. The program collects voluntary nasal swabs from passengers, as well as wastewater from both airplanes and airport facilities. These samples are then tested for the presence of pathogens.
To date, this program has been active in seven major international airports — Seattle, San Francisco, Los Angeles, Boston, New York, Newark, and Washington, D.C. Combined, roughly 300 million passengers passed through these airports in 2022.
Variants present a public health concern because they can be more infectious and resistant to treatment, making them difficult to contain. Early detection can help mitigate the spread of disease and mobilize public health resources. For example, an earlier iteration of the program detected an omicron variant of the SARS-CoV-2 virus in August 2023.
Relying on voluntary nasal swab samples has proven unpredictable, as the number of people willing to volunteer samples can fluctuate. By contrast, sick individuals involuntarily shed viruses through their waste which ends up in a community’s wastewater. Samples of this wastewater can then be collected and tested. It is important to note that viruses are inactive after passing through the gastrointestinal (GI) tract. As a result, wastewater is regarded as a useful and reliable method for monitoring public health.
Wastewater monitoring is not new. It dates back to the 1850s when scientists tracked outbreaks of cholera, a waterborne disease, in London. Though direct detection of pathogens in wastewater would not occur until the 1940s, when Drs. James Trask and John Paul detected poliovirus and linked it to outbreaks in certain states. Since then, wastewater monitoring would prove crucial to tracking emerging variants and outbreaks — especially during the COVID-19 pandemic.
Earlier this year, researchers at Rice University showed a correlation between COVID-19 wastewater monitoring and traditional metrics such as positivity rate, emergency room visits, and ICU bed rate in Houston. As asymptomatic transmission and the decrease in mandatory testing leads to an underestimation of disease prevalence, wastewater monitoring remains an invaluable tool to identify emerging pathogens and outbreaks.
Data obtained from wastewater monitoring can provide a wealth of information about affected communities, health disparities, and even be used to allocate resources. However, the implications for privacy and data equity should be considered before expanding the implementation of the program in airports and communities across the U.S.
Wastewater is a combination of public waste and thus, it is inherently more difficult to identify individuals who are affected in highly dense areas, such as an airport. This does not mean that it cannot be done. In fact, the TGS program has made data publicly available and continues to upload it to other databases. But a research group at the University of Missouri may serve as a cautionary tale.
Marc C. Johnson’s research group developed wastewater detection protocols and strategies in which they detected a cryptic, uncommon strain of COVID-19 in Wisconsin.[1] After continuous sampling and gathering publicly available data, they were able to track this cryptic lineage to a small workplace in Wisconsin. Johnson’s group then found another cryptic strain in Ohio that could be tracked to Columbus and the Washington Court House. It is still unknown whether this strain is linked to a single person, although it is likely.
Being able to deduce an individual’s pattern of movement and eventually track variants to a specific workplace presents a very real privacy concern. In addition, measures must be taken to ensure that wastewater monitoring and its resulting data is used strictly for public health purposes and not to stigmatize communities, or increase law enforcement in affected communities.
Wastewater monitoring has its benefits: It is noninvasive, does not require intensive sampling procedures, and can quickly provide data about a potential outbreak. Due to the success of these programs, the CDC is poised to expand programs like TGS on a national scale — not just at airports, but at sewersheds (community areas served by a wastewater collection system) across the U.S. As these programs are scaled up and implemented in new communities, practitioners must take care that the data is used and responsibly shared to promote health and the equitable allocation of resources. These data should not be used to promote stigma or intensify already existing health disparities.
In their current form, wastewater samples do not reveal individual data. However, it is likely that genomic surveillance systems and data will become more robust over time. As the science evolves, policymakers and practitioners must be sure to evaluate potential risks to loss of privacy.
[1] This study is a preprint and has not been peer-reviewed as of December 6, 2023.
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