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Medical diagnosis by patient feces has a long but, until recently, largely ineffective track record. The early published record dates to the mid-1600s when various guides to visual fecal characteristics were created for the guidance of physicians. Today, we apply modern high sensitivity chemical, immunological and molecular analysis on relevant bodily secretions to characterize the presence and causes of disease. For many years, wastewater testing was used to detect opioids and thereby quantify that epidemic’s spread. Most recently, one of the most effective and least invasive tests for asymptomatic colorectal cancer is Exact Sciences’ fecal DNA test.
Can poop and poop pooling analysis work for COVID-19?
COVID-19 detection is primarily focused upon respiratory secretions since this is the primary body system attacked by the causative virus SARS-CoV-2. Inhalation of infected sputum particles from the lungs through coughing and expelled air during normal breathing are the dominant routes of person-to-person transmission. Hence COVID-19 testing requires swabs of the nasal cavities and/or saliva.
While gastrointestinal symptoms themselves are relatively rare in COVID-19, about half of patients excrete detectable levels of the virus in feces. This means that poop is not consistent or reliable enough at the individual patient level, but when pooled across a community of individuals, it is quite adequate to provide an assessment of the COVID-19 prevalence and severity.
Using high sensitivity rtPCR, it is possible to detect and quantify the presence of these particles in feces in the wastewater stream, even after substantial dilution from uninfected individuals and considerable volumes of water. The process is to take samples at convenient locations and track the presence or absence of the virus over time. Any measurable change is an indicator of the prevalence of active disease in the population whose waste passes any particular sampling point. When a virus is discovered in community wastewater, more accurate testing methods can be deployed to identify and isolate infected individuals and their close contacts. This is the technique being used by several universities to monitor on-campus COVID-19 status.
In addition to colleges and universities, many states and communities are implementing wastewater surveillance systems to better estimate the prevalence of disease in the community. If sampling occurs over large sections of a city or town, it is not practical to screen each resident therein, but it does reveal the underlying problem.
The Centers for Disease Control and Prevention (CDC) and the US Department of Health and Human Services (HHS) recently announced the National Wastewater Surveillance System (NWSS). The data generated by NWSS will help public health officials to better understand the extent of COVID-19 infections in communities. The CDC is developing a portal for state, tribal, local and territorial health departments to submit wastewater testing data into a national database.
So while the COVID-19 pandemic began with our collective obsession with toilet paper, maybe it can end with our collective effort to analyze what is on that toilet paper.