Patients diagnosed with COVID-19 who have negative pharyngeal tests and are subsequently released from the hospital may not be virus free, according to a research report published in the Annals of Internal Medicine that found some patients still tested positive for the virus in sputum and feces testing.
“Pharyngeal swabs are widely used to determine the appropriateness of a patient's discharge from the hospital and whether isolation continues to be required,” Chen Chen, PhD, of the Beijing Ditan Hospital, Capital Medical University and Beijing Key Laboratory of Emerging Infectious Diseases, and colleagues wrote.
Chen and colleagues retrospectively identified a cohort of patients with COVID-19, defined by two positive pharyngeal tests, who presented at a hospital in Beijing. Patients included in the analysis had real-time quantitative fluorescence polymerase chain reaction (RT-qPCR) testing completed on pharyngeal swabs in addition to either sputum or fecal samples. Those with at least one positive sputum or fecal sample that was collected within 24 hours of a negative pharyngeal sample were further analyzed.
Patients were discharged when they no longer had a fever for a minimum of 3 days, had resolved respiratory symptoms, showed improvement on chest CT and had two consecutive RT-qPCR tests of respiratory samples obtained at least 24 hours apart that were negative for SARS-CoV-2.
The researchers evaluated 133 patients admitted to the hospital between Jan. 20, 2020, to Feb. 27, 2020. Of those, 22 patients had an initial or follow-up sputum or fecal sample test positive for SARS-CoV-2, along with a negative pharyngeal sample.
Among these patients, Chen and colleagues found that sputum samples remained positive for up to 39 days and fecal samples remained positive for up to 13 days after the negative follow-up pharyngeal sample was obtained.
“These [findings] raise concern about whether patients with negative pharyngeal swabs are truly virus free, or sampling of additional body sites is needed,” Chen and colleagues wrote.
They noted that it is not currently known whether SARS-CoV-2 detected in sputum and fecal samples is infectious, and that further research is needed.