Sleuthing the Sewage: Pondering the Poop

Reading Time – 11 Minutes, Difficulty Level 1/5

Down the drain and off the brain? 

“Flush and forget” is understandably most people’s approach to toilets and sinks – why think about sewage more than you need to? However, to sewage sleuthing scientists, a toilet flush can be full of valuable information – if your body has carried it, such as pathogens, drugs and toxins, it will eventually be found in your waste. For instance, data present in sewage and wastewater can inform researchers about the current active infections in a community, what illicit drugs may be commonplace, and even the community’s eating habits. This unique method of obtaining information about a community’s health has led to the field of wastewater-based epidemiology (WBE). WBE gained a strong foothold as a public health tool during the COVID-19 pandemic, but the field has proven helpful for a wide range of epidemiological and public health inquiries, such as community pesticide exposure and antibiotic resistance. In this article, we will discuss why, what, and how that toilet flush is a powerful tool for public health professionals, researchers, and policymakers.

This unique method of obtaining information about a community’s health has led to the field of wastewater-based epidemiology (WBE). WBE gained a strong foothold as a public health tool during the COVID-19 pandemic, but the field has proven helpful for various epidemiological and public health inquiries, such as community pesticide exposure and antibiotic resistance. In this article, we will discuss why, what, and how that toilet flush is a powerful tool for public health professionals, researchers, and policymakers.

What Exactly is Wastewater?  

To understand why wastewater is so valuable for public health professionals, defining and understanding the term’ wastewater’ is essential. Generally, wastewater is defined as water that has been ‘used’ by homes, businesses, and industries. ‘Wastewater’ is a broad term and includes both wastewater from domestic activities, like shower drains and stormwater, and wastewater from industrial practices like oil and gas production. While the terms’ wastewater’ and ‘sewage’ are often used interchangeably, there are some nuanced differences – sewage is a type of wastewater that only comes from domestic activities, such as the water and waste from sinks, toilets, washing machines, bathtubs, showers, etc. Sewage can include soap, kitchen scraps, human excrement, and toilet paper. Sewage then travels as raw sewage through sewers to wastewater treatment plants. WBE always uses wastewater, but researchers can take samples from sewage or wastewater treatment plants, depending on the research goal. 

Why is Wastewater so Useful to Epidemiologists? 

Simply – Everyone Poops. Only some people go to the doctor.

As science advanced its understanding of the infectious nature of human waste, engineers worked hard to isolate, treat, and dispose of sewage and wastewater, spending billions on plumbing and treatment plants. So why would scientists now purposely seek out and study human sewage? Perhaps Victor Hugo answered that question best in the 1862 novel Les Miserables: ‘A sewer is a cynic. It tells all.’

A community’s wastewater is often a better indicator of disease levels than clinical testing simply because everyone poops. Only some sick people will visit a doctor’s office or get tested for a given virus or bacteria, which can lead to levels of disease being underreported and underrepresented. However, because wastewater can indicate an entire community’s disease burden, we can get a better idea of the true level of disease.

The Proof is in the Pudding…errr…wastewater

As the field of WBE evolves, no virus, bacteria, pollutant, or pharmaceutical will be able to hide its presence in the community. To a public health scientist, a community’s poop and urine contain a treasure trove of information that can be used to determine real-time disease, drug, and contaminants of concern levels. In addition, disease biomarkers will often appear in wastewater much earlier before individuals even know the disease is circulating in their community, allowing for much earlier detection than clinical tools. Monitoring wastewater is also anonymous and relatively inexpensive. The benefits of WBE listed above make wastewater monitoring the perfect early warning system for public health issues, such as preventing outbreaks and identifying toxic contaminants in water.  

Combining Wastewater with Epidemiology – How it works

WBE works off the concept of ‘biomarkers.’ Short for ‘biological markers,’ are unique biological ‘fingerprints,’ such as specific proteins and hormones that can give information about the state of the body. These act as indicators for a disease state, smoking status, or even levels of stress. For WBE, a biomarker could be a variety of metabolites (in wastewater, a metabolite is a small molecule produced during metabolism and excreted in urine or feces). Researchers have identified biomarkers in wastewater for dozens of public health concerns, such as illegal drugs, viruses like polio and SARS-CoV-2, alcohol, tobacco, and even caffeine. Water samples are typically taken from a location in the sewage system before the flow reaches the wastewater treatment plant. The water samples are then ‘mined’ for metabolites and chemicals of interest that can provide information about a community’s infectious disease agents, antibiotic resistance, industrial chemicals, hormones, and even nutritional status. WBE can track increases or decreases and trends to better understand a community’s health state.    

Examples of data that Researchers can Mine:

Infectious Diseases

Wastewater surveillance for tracking levels of infectious diseases was first used for in the 1940s. However, the true usefulness of wastewater surveillance was not fully recognized until the Global Polio Eradication Initiative in 1988 when the World Health Organization (WHO) incorporated testing sewage as part of polio surveillance worldwide. WBE is advantageous for identifying infectious diseases and implementing and evaluating public health interventions in several ways. First, because many contagious viruses and bacteria are shed in the feces of infected individuals, the concentration in wastewater samples increases with the higher number of infected people in a community. This indicates the community’s viral load without requiring invasive testing or individuals visiting a doctor’s office. In addition, analyzing sewage samples can detect the presence of the virus in a community even before clinical cases are reported. This early warning system allows for a proactive response to prevent the spread of viruses or bacteria. WBE was also a significant player in understanding disease levels during the COVID-19 pandemic. For SARS-CoV-2, surveillance of wastewater proved to be an early warning sign of a community’s disease level, which allowed for a more proactive approach – earlier decision-making, better resource allocation, and prioritizing actions to limit disease spread.  

Illicit drugs and pharmaceuticals

WBE has been particularly useful in tracking illicit drug use, such as opioids and methamphetamines. Traditional monitoring of illegal drug use requires self-reporting and police data, all of which can lead to under-reporting and can be subject to bias. Using WBE for illicit drug use can give a more accurate indication of use levels in a community because it does not rely on self-reporting or other qualitative data but instead gives a quantitative measure of a community’s illicit drug use. Together with survey-based monitoring, WBE can evaluate drug abuse more comprehensively and indicate if government policies to scale down drug abuse are effective. In a similar vein, WBE has also been effective in tracking a community’s use of certain pharmaceuticals, such as ibuprofen, antibiotics, and antidepressants. By measuring exposure to pharmaceuticals in wastewater, WBE can monitor their use, provide insights into the burden of disease, and also provide insight into trends, such as the increase or decrease in the use of antibiotics due to government policies, etc.

Toxic Contaminants

Recently, WBE has been utilized to understand a community’s exposure to toxic environmental contaminants, such as pesticides, mycotoxins, nitrosamines, acrylamide, and parabens. Rapid assessment of public exposure to chemical stressors is necessary to prevent, control, or mitigate risks. WBE allows for much more rapid identification of a community’s exposure to toxic chemicals, as current methods require individual testing, which is invasive, costly, and slow. WBE can be used to assess a community’s level of exposure to dangerous contaminants and allows for a low-cost, rapid identification of potential exposure. This allows for interventions to be set in motion more quickly, reducing the possible adverse health implications. Similarly, once researchers identify a potential exposure and implement measures to minimize it, they can more easily evaluate the effectiveness of those measures.

Antimicrobial Resistance and Antimicrobial Resistance Genes

Antimicrobial resistance is a serious threat to public health. Wastewater is particularly useful for monitoring antimicrobial resistance, as it contains many known bacterial genes that confer resistance to antimicrobials. In addition, wastewater can also indicate the level of antibiotic use in a community, as antibiotics can be identified by their specific biomarkers. Analyzing the level of antibiotic use in a community alongside antibiotic-resistance genes can provide critical information on the level and presence of resistant bacterial communities in wastewater. Again, one of the significant benefits of WBE is the ability to give rapid results and respond to threats more quickly than clinical data. It also allows policymakers to evaluate the effectiveness of implemented policies, such as limiting antibiotic use to lower antibiotic-resistant genes.   

While WBE has shown immense promise as an epidemiological tool for numerous issues of public health concern, it has its challenges and limitations. Countries and cities that lack central wastewater systems, wastewater flow rates, biomarker discovery, estimates of population size serving the wastewater sample in question, and extracting the low concentrations of biomarkers from the complex mixture of wastewater are just a few of the ongoing challenges that WBE faces. These areas remain under active research, which will only make the field more robust and valuable. The COVID-19 pandemic rapidly propelled the field into the public eye and demonstrated WBE as an effective community surveillance strategy. As the field grows and our understanding and methods advance, it stands to reason that WBE will become a critical component of public health strategy and policy making, in addition to an early warning system for detecting disease outbreaks. Maybe flushing the toilet will no longer be ‘down the drain, off the brain?’

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