Clinicians from the Institute of Infectious Diseases at Beijing Ditan Hospital, Capital Medical University found that some patients had positive real-time fluorescence polymerase chain reaction (RT-PCR) test results for SARS-CoV-2 in the sputum or feces after the pharyngeal swabs became negative. Pharyngeal swabs are widely used to determine the appropriateness for a patient's discharge from the hospital and/or whether isolation continues to be required. These findings raise concerns over whether patients with negative pharyngeal swabs are truly virus-free or if sampling of additional body sites might be needed.

The clinicians retrospectively identified a convenience sample of patients admitted to Beijing Ditan Hospital, Capital Medical University with a diagnosis of COVID-19 and paired RT-PCR testing of pharyngeal swabs with either sputum or feces. Among 133 patients admitted with COVID-19 from January 20 to February 27, 2020, the authors identified 22 with an initial or follow-up positive sputum or fecal samples paired with a follow-up negative pharyngeal sample. RT-PCR positive for SARS-CoV2 of sputum and feces was seen up to 39 and 13 days, respectively, after the obtained pharyngeal samples were negative.

The researchers caution that the study was not carried out in a systematic fashion with sampling of all patients in a protocolized manner, and it is not known whether these positive sputum or fecal results indicate that the patient could still be infectious to others. However, their findings are potentially important because they suggest that more study is needed in this area.