The COVID-19 virus may be present in GI tract and faecal samples of recovered patients for weeks after respiratory samples are negative, clinicians in China have found.

In a study of respiratory and faecal test samples from 74  patients with COVID-19 they found that 41 (55%) had faecal samples that were positive for SARS-CoV-2 RNA.

In these patients the respiratory samples remained positive for SARS-CoV-2 RNA for a mean of 16·7 days after first symptom onset and faecal samples remained positive for a mean of 27·9 days (ie, an additional 11·2 days after respiratory samples were negative).

In two notable patients the faecal samples remained positive for SARS-CoV-2 at 33 days and 47 days respectively after their respiratory samples tested negative for the virus.

Prolonged duration of SARS-CoV-2  in faecal samples was not associated with gastrointestinal symptoms or disease severity but was associated with antiviral treatment.

Doctors at the at the Fifth Affiliated Hospital of Sun Yat-sen University, Zhuhai, said a positive faecal test did not necessarily mean viral viability, but the findings nevertheless “suggest the possibility of extended duration of viral shedding in faeces, for nearly five weeks after the patients’ respiratory samples tested negative for SARS-CoV-2 RNA.”

This implied that the COVID-19 virus is actively replicating in the patient’s gastrointestinal tract and that faecal–oral transmission could occur after viral clearance in the respiratory tract, they wrote in Lancet Gastroenterology and Hepatology.

However they cautioned that there had yet to be any confirmed reports of faecal-oral transmission of COVID-19, although this had been seen with previous coronavirus outbreaks involving as seen with SARS CoV and MERS CoV.

The finding of prolonged viral shedding suggested that routine stool sample testing with real-time RT-PCR should continue for patients after the clearance of viral RNA in a patient’s respiratory samples, they concluded.

“Strict precautions to prevent transmission should be taken for patients who are in hospital or self-quarantined if their faecal samples test positive,” they recommended.

The findings also raised the question of how long to continue quarantine precautions to prevent transmission in patients who have recovered from COVID-19.

Currently, a decision to discharge a patient may be made if they show no relevant symptoms and at least two sequential negative results by real-time RT-PCR of sputum or respiratory tract samples collected more than 24 h apart.

But in the Chinese patients there were no or very mild symptoms reported after respiratory tract sample results became negative.

“No cases of transmission via the faecal–oral route have yet been reported for SARS-CoV-2, which might suggest that infection via this route is unlikely in quarantine facilities, in hospital, or while under self-isolation,” the authors wrote.

“However, potential faecal–oral transmission might pose an increased risk in contained living premises such as hostels, dormitories, trains, buses, and cruise ships.”