As states and countries begin to reopen and people come in closer contact, public health officials worry about the potential for new COVID-19 outbreaks. Vigilance and infection monitoring can help identify new COVID-19 cases before they spread throughout communities. However, current testing measures have limitations that may preclude early detection and prevention. Many counties in the United States (U.S.), for example, lack testing sites. Similarly, the timing of viral testing can be too late to halt significant spread. Individuals usually get tested for the virus, using a nasopharyngeal swab, only after they have symptoms. Unfortunately, they may have been contagious for up to 3 days before feeling anything. With current testing procedures and timing, people can easily spread the virus to others and a surge in cases may already be underway.
Rather than waiting for the presence of infection, which signals that others have been exposed to, and possibly contracted, the virus, scientists are exploring a more proactive way to monitor COVID-19 in communities: sewage testing. Researchers take samples of fecal matter (yes, poop!) from sewage treatment plants and measure coronavirus particles. These particles represent small genetic parts of the virus that can indicate whether people from within that sewage plant’s distribution are shedding virus before they develop symptoms. Not only does this have the potential to predict possible hot spots, it also offers convenience and the efficiency of wider spread testing. Fecal sampling (also called wastewater testing) allows experts to monitor viral levels across a large group of people without requiring in-person testing. Researchers quantify the particles detected to estimate how many people in the region may be carrying the coronavirus. This can allow for isolation of specific neighborhoods at high risk for outbreaks before they occur by testing the wastewater of areas upstream of the sewage plant.
Similar testing has been applied globally to test for poliovirus, hepatitis A, and norovirus to predict risk of each of these infections in a given region
Testing Ramp Up
COVID19 can infiltrate cells lining the gut, causing viral particles to shed in the feces up to one to two weeks before symptoms begin.
The idea of sewage testing may seem unpleasant. But, COVID19 can infiltrate cells lining the gut, causing viral particles to shed in the feces up to one to two weeks before symptoms begin. Feasibility simulations, run by Drs. Hart and Halden of Arizona State University, estimate that current methods of testing for COVID-19 particles in the sewage can detect infection of a single person in the fecal matter of between 100 and 2,000,000 people. In France, researchers looked back at fecal samples from the month surrounding the outbreak’s peak; fecal viral levels accurately predicted the rise in COVID-19 cases in Paris. In the U. S., many efforts like the collaboration between Clean Water Services and Oregon State University, the startup company BioBot, and several state-sponsored projects (including, California, Washington, Utah, and others), are already sampling in many cities across the country. Their data seems to accurately predict increases in cases in the affected towns. It’s now a matter of ramping up testing coverage and integrating the insights from the sewage with directed public guidance on protective measures to take. Great Britain and Wales are also exploring ways to apply sewage monitoring of COVID-19 more broadly to know how to interpret the information and prevent second waves of coronavirus infections in those countries.
Early detection of potential COVID-19 cases from sewage testing will allow public health officials to take early action
If experts know that a group of people have been infected but have not yet become symptomatic, they can target guidance on quarantine measures, procure increased swab testing, and direct medical personnel and resources (e.g. PPE and mechanical ventilators) to the impacted area. These steps might prevent large-scale infectious spread without disrupting the lives and routines of uninfected areas, protect healthcare providers, and make sure that adequate equipment is available to treat those who become sick. Moreover, according to Drs. Hart and Halden, each fecal test kit costs, on average, only $15. The lower cost and broader sampling measures compared to swab testing could extend the value to larger groups of people and save money.
Downside of Fecal Testing
Sewage testing has its limitations. Infections from homes whose septic systems don’t connect to public sewage plants would be missed. Additionally, transit time within sewage pipes and environmental factors, like hot temperatures, affect how quickly viral particles degrade. This means that the test might be less accurate in detecting infections from buildings farther from the sewage plant and/or during the summer. Also, a critical factor to understand is that sewage testing combines samples from many people all together. This method could not tell an individual person whether they should isolate or quarantine and could not replace traditional swab tests, especially for those who have symptoms. But sewage testing in combination with existing detection methods may provide additional data that can help policy stay ahead of potential outbreaks. It may have application for predicting resurgences and second waves or peaks; as such, communities might be able to shed light on whether measures to reopen are safe, including for schools and businesses.
Much is still uncertain about how the reopening process will affect the course of coronavirus spread. It’s important to approach these new phases with caution and use social distancing measures wherever possible. But large-scale, careful monitoring of the sewage may help predict where additional precautions should be directed while allowing normal activity in disease-free zones.
By Arpita Jajoo; Edited by Dr. Jacki Hart