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Updated: Mar 31, 2020 18:18 IST

Chinese doctors have found the novel coronavirus in the sputum and faecal samples of some patients with negative pharyngeal swabs for COVID-19.

The study, published in the journal Annals of Internal Medicine, found that some patients had positive, real-time fluorescence polymerase chain reaction (RT-PCR) test results for SARS-CoV-2 in the sputum or faeces after the pharyngeal swabs became negative.

Pharyngeal swabs are widely used to determine the appropriateness for a patient’s discharge from the hospital and whether isolation continues to be required, said researchers from the Capital Medical University in China.

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 with a diagnosis of COVID-19 and paired RT-PCR testing of pharyngeal swabs with either sputum or faeces.

Among 133 patients admitted with COVID-19 from January 20 to February 27, 2020, the researchers identified 22 with an initial or follow-up positive sputum or faecal samples paired with a follow-up negative pharyngeal sample.

RT-PCR positive for SARS-CoV2 of sputum and faeces 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 protocolised manner, and it is not known whether these positive sputum or faecal results indicate that the patient could still be infectious to others.

However, the findings are potentially important because they suggest that more study is needed in this area, the researchers said.