Public health decision-makers are left with few options to understand the spread of the virus in communities and populations due to the rapid transmission of the COVID-19 Omicron variant. This has led to a new phase of the pandemic, one in which conventional public health surveillance methods such as PCR tests or at-home antigen tests are insufficiently available to provide useful information on how many people are infected, where, and when.
In this context, one notable exception is the use of wastewater surveillance or wastewater-based epidemiology (WBE) as a public health surveillance tool.
How wastewater testing works
Early in the current pandemic, fragments of SARS-CoV-2—the virus that causes COVID-19—was discovered in human feces. The virus is detectable in stools as soon as people become infected, days before they develop symptoms and even if they remain asymptomatic. Wastewater testing uses the same PCR test that is used for clinical testing, a test that is so sensitive that SARS-CoV-2 can be detected even when wastewater is diluted with rainwater or mixed with industrial effluents.
Testing can be done on samples collected anywhere that wastewater flows or is treated, for example outlets at specific locations, wastewater lagoons or open trenches, or large treatment facilities in areas with well-developed collection systems.
The case for investing in wastewater-based epidemiology
. In communities worldwide, signs of Omicron have been discovered in wastewater before clinical cases were reported. In South Africa, for example, the presence of SARS-CoV-2 in wastewater rose quickly, as the Omicron variant took hold; while in the United States, in many large cities such as Houston, Texas, Omicron was detected in wastewater days before clinical tests came back positive.
The resource requirements for wastewater testing are typically much lower than for clinical testing. The total cost of clinical testing increases considerably during surges and waves, whereas for wastewater testing the cost generally remains constant.
Wastewater testing is typically performed two to three times each week, but the frequency can increase or decrease depending on the level of circulating SARS-CoV-2.However, costs can vary from US$0.20 to over $3 per person depending on the proportion of the population served by wastewater treatment facilities, the frequency of testing, and other factors.
For example, wastewater can be a lens into the broader health of our communities. A single sample can be analyzed for a variety of pathogens: influenza, hepatitis A, polio, antimicrobial resistance, and other diseases. The proportion of different variants, including Omicron, can be assessed.
Wastewater in Latin America and the Caribbean
Of the 3,000+ wastewater testing sites worldwide, most are in high-income countries. Although wastewater testing is not a replacement for clinical testing, it is well suited to low- and middle-income countries. The value is particularly clear when testing capacity is overwhelmed, as we are currently seeing with the Omicron variant.
Pilot sites have begun in an increasing number of sites in LAC such as Ecuador and Argentina. This is relevant both during peaks of pandemics but also during lower levels of contagion as a low-cost instrument to monitor levels of infections of populations with the virus.
With the rapid expansion of wastewater testing during the COVID-19 pandemic, some important challenges have emerged and may be resolved by implementing practical interventions detailed in the World Bank Guidebook on wastewater-based epidemiology.
Building the partnerships and infrastructure needed for successful wastewater testing can take time. But investments today can reap long-term benefits by strengthening a country’s ability to mount a timely, well-informed response for a range of public health issues.
This is what is leading the United States and Europe to massively invest in wastewater-based epidemiology to prepare better for future pandemics.
. This is an affordable, effective, and a smart investment, an ally to clinical testing and a low-cost surveillance approach well suited to low- and middle-income countries.