Conversion of pharyngeal specimens from SARS-nCoV-2-positive to negative may not correlate with end of viral shedding

1. In this study conducted in China, several patients with SARS-CoV-2-negative respiratory samples had sputum and feces that remained positive for several weeks.

2. A number of patients had respiratory samples revert to SARS-CoV-2-positive during hospitalization. This suggested the need for further research regarding the relationship between nucleic acid testing and infectivity.

Evidence Rating Level: 3 (Average)

Study Rundown: Given the high transmissibility of SARS-Cov-2, isolating infectious individuals is essential in controlling the spread of the virus. Testing of respiratory specimens through real-time quantitative fluorescence polymerase chain reaction (RT-qPCR) is the current standard for detection, but it is unknown whether this metric alone is adequate for the evaluation of infectious risk. This study found that sputum and feces samples from patients with COVID-19 continued to test positive for SARS-CoV-2 weeks after follow-up pharyngeal samples had become negative. This finding suggests that a negative swab from a single body site may not indicate that a patient is truly virus-free; rather, it may be necessary to sample additional sites for confirmation. While this study was based on a convenience sample and did not adhere to a strict protocol, these results highlight the need for further research into this area.

Click here to read the article in Annals of Internal Medicine

Relevant Reading: Positive RT-PCR Test Results in Patients Recovered From COVID-19

In-Depth [case series]: In the period from 20 January to 27 February 2020, 133 patients were admitted to Beijing Ditan Hospital, Capital Medical University with a diagnosis of COVID-19. Of these patients, 22 were identified to have had a positive fecal or sputum sample paired with a follow-up negative pharyngeal swab. 14 patients were male, and 18 were between the ages of 15 and 65. For the majority of patients, fever was the first symptom and the disease did not progress beyond mild pneumonia. 545 specimens, including 209 pharyngeal swabs, 262 sputum samples, and 74 feces samples, were collected over the course of ~55 days. Sputum and feces samples were found to remain positive for up to 39 and 13 days, respectively, after negative conversion of pharyngeal samples. While a criterion for hospital discharge was two consecutive negative samples at least 24 hours apart, multiple patients were found to have met this criterion and tested positive again at a later date. These findings suggest the importance of repeat testing as well as testing in multiple body sites.

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