by Mechas
Using wastewater to monitor human populations is a growing trend. The waste products found in this water, discarded after domestic, commercial, or industrial use, reflect the habits and consumptions of society and provide a pool of information on our customs and behaviors. The recent surge in interest on analyzing wastewater stems from its value for probing pathogens and informing on health concerns that aid public health decisions.
The Cloaca Maxima under the Roman Forum, photo credit Marco Gradozzi. Source.
Archeological remains indicate that disposing of human wastes and wastewater has troubled people for millennia. Systems to remove wastes from urban centers were present in the Mesopotamian Empire, in Ancient Greece, and, of course, in Rome. Romans, who excelled as architects and engineers, constructed complex systems to both transport water and remove wastewater from urban centers, an example of the latter being the large and impressive Cloaca Maxima. But more often than not, wastes were disposed of in streets and public places, frequently resulting in serious health problems and pandemics, as occurred throughout Europe during the Middle Ages.
Only until recently in human history have we understood the importance of wastewater management and sanitation to public health. And even more recently have we realized the value of using wastewater for pathogen surveillance. Tracking pathogens in wastewater rose to prominence during the COVID-19 pandemic as an easily accessible scheme for probing nearby populations without invasive testing. This approach was quickly implemented in many countries as a rapid and cost-effective strategy for community surveillance, providing early warning of possible SARS-CoV-2 outbreaks. Since then, interest in wastewater-based epidemiology has surged. The sensitivity of molecular methods, particularly targeted PCR techniques and metagenomic sequencing, can accurately identify potential pathogens and other threats to public health.
Despite this recent burst of activity, the use of urban sewage to track viruses is not new. Wastewater was used as early as 1939 to track poliovirus. Only much later, in 2003, was wastewater-based epidemiology formally recognized by the World Health Organization and by 2020, when we were hit by the COVID-19 pandemic, it was an established and reliable method for public health monitoring. Today, it is used to identify other viral pathogens like influenza virus and respiratory syncytial virus. But wastewater contains more than just pathogens. It has been used recently, for example, to monitor consumption trends, such as illicit drug use, and to determine the presence and spread of antibiotic-resistance genes.
Wastewater has played at least one other prominent role in microbiology. It was at the root of work done by the Phage Group and thus critical in the early history of molecular genetics. As described in a previous post, the physicist Max Delbrück met Emory Ellis at Caltech. Before meeting Delbrück, Ellis was already working with phages. His aim was to replicate and expand Felix d'Hérelle's growth experiments which indicated that phages were parasites – analogous to plant and animal viruses – that multiplied in bacteria. For this, Ellis sampled a site likely to contain phages: the sewage system of Pasadena, California. W.C. Summers documents this in a paper on the use of bacteriophage by the Phage Group: "Ellis, together with his wife, Marion Ellis, obtained some sewage from the Pasadena sewage treatment plant and, following d'Herelle's methods, isolated a phage active on E. coli."
The encounter between Delbrück and Ellis set the stage for using E. coli and its phages as a key model system, work that proved foundational for molecular biology. But why did Emory Ellis select E. coli? This serendipitous choice will be explained in next Monday's post. Stay tuned.
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