Wastewater Epidemiology for Biosecurity – Demystified
This project was runner up for the "Simple Explainer" prize on our Pandemics (May 2024) course. The text below is an excerpt from the final project.
Introduction
Imagine a tool that can spot the spread of a virus before anyone even shows symptoms. It might sound like science fiction, but this is the promise of wastewater-based epidemiology - sometimes called WBE or wastewater epi. In this explainer, I’ll explore the basics of this powerful public health tool, its limitations, and what we can expect from it in the future.
The Challenge: How Do We Detect Outbreaks Early?
It’s the early hours of an outbreak - doctors suspect a highly concerning virus when they diagnose one or a few patients. To have any chance of containment, public health professionals race to learn how many people are sick, where they are, and whom they have contacted. Equally important, they calculate measures like basic and effective reproduction numbers, generation time, serial intervals, and lethality - these help characterize the outbreak’s scale, severity, and containability.
What do these words mean?
- Basic reproduction number (R0): How many people one person can infect when no one is immune and no protections are in place.
- Effective reproduction number (Rt): How many people one person is actually infecting at a specific time, considering factors like immunity or prevention measures.
- Generation time: The average time between someone getting infected and passing it to someone else.
- Serial intervals: The time between when one person shows symptoms and when the person they infected shows symptoms.
- Lethality: The percentage of people who die from the virus out of those who get infected.
Patient-level testing and contact tracing are, of course, the first and most important steps to determine how an outbreak should be addressed. However, traditional diagnostics have limitations and rely heavily on human behaviors. Patients may not be tested if they are asymptomatic, lack access to testing services, or simply do not want to test. Even if patients are tested, results can be delayed or inaccurate. When patients use at-home rapid tests, most results will never get reported to public health officials. Additionally, privacy regulations require the removal or masking of personal identifiers before data is aggregated and shared, which can further slow down the reporting process.
To be clear, wastewater epi should be used to complement patient level testing, not replace it. WBE doesn’t tell us which individual is sick, how severe their illness is, or with whom they have been in contact. We will always need patient-level data to answer those questions. But wastewater can help fill in gaps left by patient-level testing, by telling us sooner, more accurately, and more cheaply if and how much of a virus is circulating within a community.
Testing challenges in action
At the start of COVID-19, patient-level testing faced significant challenges. The U.S. CDC's initial tests were flawed, and strict federal testing criteria delayed diagnoses, even for patients showing symptoms. By late February 2020, fewer than 4,000 tests had been conducted nationwide, meaning there was little understanding of the scale and severity of the outbreak. In fact, it wasn't until researchers from the Seattle Flu Study—defying federal and state guidelines—tested flu samples for COVID-19 that community transmission was confirmed.
Getting on the Same Page: What Is Wastewater-Based Epidemiology?
Before diving in, let’s clarify a key distinction between wastewater epi and environmental wastewater monitoring.
Environmental wastewater monitoring usually means a focus on water quality and addressing Clean Water Act concerns like pollution, factory runoff, and contamination. Wastewater epi, on the other hand, looks at wastewater samples to understand the health of a community. Instead of checking for pollution, it checks for things like viruses, chemicals, or even drugs to see what might be circulating in a population. These two types of wastewater monitoring do not need to be mutually exclusive; however, they generally involve different priorities, methods, and stakeholders.
While people usually talk about wastewater epi in terms of biological concerns, like viruses, it can also be used to look at chemicals. Analyzing chemicals in wastewater has been a helpful tool in combating the opioid epidemic.
We could talk all day about wastewater epi, but for the sake of brevity, for the rest of this explainer we will focus specifically on how biological wastewater epi is used in the U.S.
Full project
You can view the full project here.