The lavatory lens: Tracking the global movement of pathogens via aircraft wastewater

Modern commercial air travel connects disparate human populations. The global airline industry transported as many as 4.5 billion passengers annually in the years leading up to the COVID-19 pandemic. While such connections are convenient for commerce and tourism, air travel networks can also be efficient distributors of infectious diseases. During the COVID-19 pandemic, public health agencies used multi-layered control strategies to manage the risk of COVID-19 transmission associated with air travel. Simultaneously, the surveillance of aircraft wastewater was further developed as a promising new method to screen for COVID-19, including newly emerging lineages, among international travelers. Herein, we review the potential of aircraft wastewater for public health surveillance. The known itinerary and defined passenger population along with the highly concentrated waste stream and ease of sampling during routine ground handling make aircraft wastewater a strategic opportunity for unintrusive surveillance of the global circulation of human pathogens. We estimate in the case of a fecal- or urine-shed pathogen, surveying 10% of all global long-haul flight passengers would require sampling from 3,500 and 1,250 flights per week, respectively. In the case of the United States, achieving 10% coverage of all international arrivals would require sampling from 925 and 322 flights per week for each shedding pathway, respectively. Aircraft wastewater surveillance can also be integrated with network and infectious disease models to better target traditional public health control measures during epidemic onset. Given the demonstrated potential for public good and the tremendous economic costs of epidemics, governments should consider international collaboration and investment to create a global aircraft wastewater surveillance system.