January 2023. China reopens its international borders after nearly three years of strict COVID-19 controls. European governments, uncertain what viral variants might be circulating among Chinese travelers, scramble for surveillance intelligence. Some reinstate testing requirements for flights from China. Others implement airport wastewater programs. Brussels Airport does something more ambitious.

The study

Researchers at the Rega Institute and the University of Leuven, working with Brussels Airport authorities, collected wastewater samples from 32 direct flights arriving from Beijing between January and February 2023 — the weeks immediately following China's border reopening [1]. They then applied hybrid-capture metagenomic sequencing using Twist Bioscience enrichment panels, a method designed to detect not just known viral targets but any viral genomic material present in the sample.

Of the 32 samples:

  • 19 tested positive for SARS-CoV-2
  • The detected lineages included BA.4, BA.5, and XBB — confirming that the COVID variants circulating on these flights matched patterns then emerging globally

But the SARS-CoV-2 findings were not the most significant part of the study.

What the metagenomics revealed

Beyond COVID-19, the hybrid-capture approach recovered complete or near-complete genomes from viruses in multiple families that targeted PCR panels would have entirely missed:

  • Polyomaviridae — a family of viruses that includes BK virus and JC virus, which can cause serious disease in immunocompromised individuals
  • Papillomaviridae — human papillomaviruses, which are shed in skin and mucosal cells
  • Herpesviridae — including Epstein-Barr virus (EBV) and cytomegalovirus (CMV), both of which are latent in a significant proportion of the global population
  • Hepatitis B virus (HBV) — a bloodborne pathogen that can also be shed in saliva and feces

Finding Hepatitis B in aircraft wastewater is not, in itself, alarming — HBV is endemic in many parts of the world, and its presence on a flight from Beijing reflects the epidemiology of the departure region. But its detection illustrates the breadth of what metagenomic sequencing can capture: the full virome of the passenger population, not just the targeted subset.

The intelligence value for under-surveilled regions

The study makes an important argument that extends beyond Beijing. Aircraft wastewater, the researchers argue, is an especially valuable intelligence source precisely when the departure region has limited domestic genomic surveillance [1]. If a novel variant is circulating in a country where clinical sequencing rates are low or nonexistent, it will not appear in GISAID until it spreads to a country with dense surveillance. But it will appear in the wastewater of inbound flights — because the surveillance happens at the destination airport, not in the departure country.

This is the global equity argument for aircraft wastewater surveillance. It does not require the departure country to have laboratory capacity. It captures the pathogen biology of the passenger population regardless of where those passengers came from, what infrastructure existed there, or whether any local surveillance program would have noticed the variant at all.

The Brussels lesson for Bangkok

Suvarnabhumi handles direct flights from dozens of countries across Asia, the Middle East, and Africa — including countries with genomic surveillance programs that range from sophisticated to essentially nonexistent. A metagenomic surveillance program at BKK would capture the virome of passengers from all of those departure regions, simultaneously, passively, and without requiring anything from the countries they came from.

The Brussels study used one of the most powerful sequencing methods currently available. A starting operational program at Suvarnabhumi would likely begin with targeted PCR panels — faster and more cost-effective — with metagenomic capacity added as laboratory infrastructure matures. That sequencing step is what catches the unknown: the variant that does not yet have a name.

The choice between targeted PCR and metagenomic sequencing is not either/or. It is a progression — and the Brussels study documents what lies at the end of that progression.