COVID-19 can be detected for longer in the feces than in the respiratory tract. But further studies are required.
In March 2020, researchers showed the virus that causes COVID-19 stays in the feces. The paper, which was published in the Lancet, suggested that the virus "shed in the feces(stools) for nearly five weeks after the patients' respiratory samples tested negative for COVID-19 RNA." They advised routine stool sample testing with real-time RT-PCR after the clearance of viral RNA in a patient's respiratory samples.
A paper in the American Society for Microbiology also showed that COVID-19 was detected in the upper respiratory tract after "two to three weeks post-symptom-onset in most patients." On the other hand, COVID-19 was detected in the "stool of some patients for greater than four weeks."
The CDC's journal has also described how the virus was detected in the fecal matter of an asymptomatic child up to 17 days after exposure to COVID-19. Respiratory tract specimens were negative by reverse transcription PCR. However, there were limitations, such as delay in RT-PCR testing after the first recognition of the virus.
National Geographic reported Andrew Karaba, an infectious disease fellow at Johns Hopkins University, explained that: "A PCR test can tell you whether someone has recently caught the disease, but it cannot distinguish between the live replicating virus and non-infectious viral debris. Even when the virus is no longer infectious, there's a period of time when you can still detect its RNA."
Other research has concluded that "stool testing cannot solely be used to rule out disease since not all patients shed viral RNA in the stool" and that "the use of stool testing should be limited and utilized only after results of upper respiratory PCR are available."
The COVID-19 pandemic has given rise to a lot of potentially dangerous misinformation. For reliable advice on COVID-19, including symptoms, prevention, and available treatment, please refer to the World Health Organization or your national healthcare authority.