Spit and feces test positive for SARS CoV-2 even after recovery

A new study reveals that samples of sputum and feces continue to test positive for the severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2) virus even after a person has recovered from COVID-19 and nasopharyngeal secretions test negative for the virus.

The study from researchers at the Institute of Infectious Diseases at Beijing Ditan Hospital, Capital Medical University, appeared in the latest issue of the journal Annals of Internal Medicine. The study is titled, “SARS-CoV-2–Positive Sputum and Feces After Conversion of Pharyngeal Samples in Patients With COVID-19”.

Novel Coronavirus SARS-CoV-2 Colorized scanning electron micrograph of a VERO E6 cell (blue) heavily infected with SARS-COV-2 virus particles (orange), isolated from a patient sample. Image captured and color-enhanced at the NIAID Integrated Research Facility (IRF) in Fort Detrick, Maryland. Credit: NIAID
Novel Coronavirus SARS-CoV-2 Colorized scanning electron micrograph of a VERO E6 cell (blue) heavily infected with SARS-COV-2 virus particles (orange), isolated from a patient sample. Image captured and color-enhanced at the NIAID Integrated Research Facility (IRF) in Fort Detrick, Maryland. Credit: NIAID

What was the study about?

The world has been brought down to its knees by the novel coronavirus or SARS-CoV-2, causing COVID-19 disease. Since declared a global pandemic, the number of cases and deaths due to the disease has steadily climbed. As of today, the total number of cases globally is 858,785 and the infection and its complications have killed 42,151 individuals. There are no specific therapies for COVID-19 nor vaccine for SARS-CoV-2 infection. At present, the only available options are the diagnosis and isolation of the positive patient to prevent transmission to others and treatment of the symptoms such as fever, and in more severe cases, difficulty breathing.

For diagnosis, real-time quantitative fluorescence polymerase chain reaction (RT-qPCR) testing of nasopharyngeal secretions for SARS–CoV-2 RNA is used. At present, apart from respiratory specimens, other specimens are also used for the detection of the virus. The specimens that test positive for the virus on RT-qPCR include blood, feces, and urine. However, there are no studies that look at the efficacy of testing multiple sites in the body for the virus.

The main aim of this study was to look at the results of RT-qPCR for SARS–CoV2 RNA from sputum as well as fecal samples of patients who tested negative for the virus in their nasopharyngeal samples.

What was done?

The study team looked at the admitted patients from the Beijing Ditan Hospital, Capital Medical University. They had all tested positive using paired RT-qPCR testing of their pharyngeal swabs and either their sputum or feces samples. For a positive diagnosis, at least 2 RT-qPCR–positive pharyngeal swabs are needed wrote the researchers. The patients were treated symptomatically, and at the end of their treatment course, the patients had to meet four criteria before they could be discharged from the hospital. These included;

  • No fever for three consecutive days
  • No respiratory symptoms
  • Significant improvement in the chest CT scan findings
  • Two consecutive negative RT-qPCR tests for SARS–CoV2 in the respiratory secretion samples. These two samples are to be taken at least 24 hours apart.

For this study, the team looked at least 1 follow up RT-qPCR positive sample of sputum or feces in the patients at least 24 hours after they had tested negative in their respiratory samples.  RT-qPCR assay, wrote the researchers looked at the “open reading frame 1ab (ORF1ab) region” and the “nucleoprotein (N) gene” along with negative control. They explained that the cycle threshold value they decided on was 37 or less, and Chinese national guidelines were followed to determine positive results.

What was found?

The researchers assessed samples of 133 patients who were admitted with COVID-19 between 20 January and 27 February 2020. The patients included 18 who were aged between 15 and 65 years and 4 children. 11 of the patients had a history of travel to regions where there were clusters of COVID-19 or had been exposed to an individual who had returned from Hubei Province in China in the last month. One of the most prevalent symptoms of the patients was fever. Five of the patients had at least one comorbid disease. From these, they identified 22 who had an initial or positive result from sputum and fecal samples paired with negative nasopharyngeal samples. A total of 545 samples were collected from the 22 patients, and these were 209 pharyngeal swabs, 262 samples of sputum, and 74 samples of feces.

All the enrolled patients met the criteria for hospital discharge and were subsequently discharged. The researchers noted that RT-qPCR positivity persisted in the sputum and feces for up to 39 and 13 days, respectively, even after the pharyngeal samples tested negative.

Limitations of the study

This study was not performed under usual protocols, say the researchers. They said the study was not conducted in a systemic manner, and it was still not clear if these patients testing positive in their sputum and fecal samples were a danger to their contacts. The team explains that sampling for this study was “convenience sampling.”

Conclusions and implications

This study reveals that there is much scope for study regarding the persistent presence of the virus in various bodily secretions and its implications in transmission. The team wrote, “These results warrant further study, including the systematic and simultaneous collection of samples from multiple body sites and evaluation of infectious risk.”

Journal reference:

Chen C, Gao G, Xu Y, et al. SARS-CoV-2–Positive Sputum and Feces After Conversion of Pharyngeal Samples in Patients With COVID-19. Ann Intern Med. 2020; [Epub ahead of print 30 March 2020]. doi: https://doi.org/10.7326/M20-0991

Dr. Ananya Mandal

Written by

Dr. Ananya Mandal

Dr. Ananya Mandal is a doctor by profession, lecturer by vocation and a medical writer by passion. She specialized in Clinical Pharmacology after her bachelor's (MBBS). For her, health communication is not just writing complicated reviews for professionals but making medical knowledge understandable and available to the general public as well.

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