Big poo, big data: what your poo says about you

Have you thought about how much you poop and pee every day? More importantly, what crucial data from your excreta are you flushing away?

It may surprise you that a healthy adult produces about 320 lbs (145 kg) of excrement yearly — just a little more than the weight of an adult panda, and anywhere between 400 to 2,000 millilitre of urine a day or about 34,400 litres in a lifetime, equivalent to 46 hot tubs. Scientists are becoming increasingly aware that this gunk is more than just a bad smell; it holds crucial information, which can be collected through a process called wastewater analysis. Specifically, getting health information through wastewater analysis is called wastewater-based epidemiology and is a well-established scientific practice. For example, scientists have used wastewater-based epidemiology to track the genetic material of SARS-CoV-2, the virus that causes COVID, to track its spread. 

How wastewater-based epidemiology works

Scientists can identify SARS-CoV-2 in the wastewater of a large population and quantify how much of it there is. Knowing how much SARS-CoV-2 is in wastewater leads to an understanding of what percentage of that population has COVID. Below is an example of wastewater-based epidemiology (Figure 1). It is different from clinical COVID tests such as RT-PCR or ART tests, which focus on individuals, in that it finds the rate of COVID infection in an entire population or community so that we know which population is more or less affected by the virus.

The US has spent approximately 200 billion dollars to manually test a large sample of people to get information on COVID infection rates. That’s a significant amount of money diverted from other parts of the economy. Wastewater-based epidemiology provides a cheaper and faster way to gather such information. Compared to the $200 billion dollars that were spent on manual testing in the US,  wastewater-based epidemiology, which costs between $150-$300 USD, is clearly a much more frugal alternative. It is also very fast; it can predict a COVID outbreak in around 4 to 5 days. That’s one week earlier when compared to clinical testing, in fact, even before people begin showing symptoms.

Other applications of wastewater-based epidemiology

A technique like this is useful for other applications also. Wastewater-based epidemiology has, for example, been used to track illicit drug use by analysing drugs and their metabolites in the wastewater. Immediately after consumption, these drugs undergo a series of biochemical reactions in our bodies and are finally excreted as active drugs or metabolites. In one study, wastewater was analysed in 80 European cities and revealed the flow of active drugs with the exact information on where and when this drug use took place. Wastewater-based epidemiology has also been used to identify Alzheimer’s, Parkinson’s and Huntington’s diseases, and even antimicrobial resistance forming in a population (Figure 2). It was also used to study other viral outbreaks, including influenza outbreaks in the US. Such analyses therefore hold immense value, potentially saving billions of dollars and enabling policymakers to respond faster. 

Challenges

The accuracy of wastewater-based epidemiology depends on several factors. These factors could be as simple as the volume of the sample and the sampling time, to more complex things like sample preparation and instrument detection levels (Figure 3).

Collecting as many samples as possible may sound good at first. However, quality trumps quantity in this case. In fact, fewer but more proportional samples that represent a large sewage catchment/area may provide better information. Impurities present in the wastewater may also derail the analysis of these biomarkers, even with the use of different measurement instruments such as Fluorescence Spectroscopy, High Resolution – Liquid Chromatography – Mass Spectrometry (HR-LC-MS), and digital PCR (dPCR). The temperature and condition at which viral RNA or chemical markers are stored are also critical considerations. 

Nonetheless, these challenges are inconsequential when compared to the benefits of wastewater-based epidemiology. With 1 millilitre of concentrated wastewater, we can discover a significant amount of information, making wastewater-based epidemiology a breakthrough that can change the face of public health.