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An international team of scientists who spent five years studying the poo of 647 Danish babies found something astonishing. The nappy samples contained 10,000 species of virus—10 times the number of bacterial species in the same children. Most of the viruses had never been described before.

This may alarm many readers. Viruses haven’t exactly had a good reputation in recent years. But what many people don’t realize is that the overwhelming majority of viruses do not make people sick and do not infect humans or animals at all.

The viruses I’m referring to are bacteriophages. They exclusively infect bacteria and make up a large part of the human microbiome. It’s these bacteriophages that the researchers found so abundantly in baby poo. Indeed, around 90 percent of the viruses found in the nappies of the Danish babies were these bacteria killers.

Enlarge / A bathroom on an Airbus A321neo. (credit: Getty | Nicolas Economou/NurPhoto )

The US Centers for Disease Control and Prevention is considering blending sewage sampling from airplanes into the mix of its wastewater surveillance system, which has proven useful for monitoring the spread and prevalence of a variety of pathogens, particularly SARS-CoV-2.

Amid the pandemic, the CDC launched wastewater testing programs across the nation, trying to get ahead of SARS-CoV-2 surges. Viral particles are often shed in fecal matter and can be an early indication of an infection. The fecal focus has proven useful for sniffing out community-wide transmission trends and disease spread for not only COVID-19 but also other recent outbreaks as well, namely polio and mpox (formerly monkeypox). Adding surveillance from airplanes and airports could flush out yet more information about infectious disease spread, such as global travel patterns and the debut of novel viral variants.

A study published last week in PLOS Global Public Health found such sewage surveillance in UK airport terminals and airplanes was effective at tracking SARS-CoV-2 among international travelers. Overall, the surveillance data suggested that it is a "useful tool for monitoring the global transfer rate of human pathogens and other disease-causing agents across international borders and should form part of wider international efforts to monitor and contain the spread of future disease outbreaks," the authors, led by Kata Farkas of Bangor University, concluded.