A timeline for viral shedding of coronavirus disease 2019 (COVID-19) in the stool has been published in Gastroenterology. According to study data, viral ribonucleic acid (RNA) persisted for a longer duration of time in the feces than in respiratory samples from the same patients, suggesting that rectal swabs may be crucial in the diagnosis and management of COVID-19.

Samples were collected from 401 patients admitted to the Shenzhen Third People’s Hospital in China for the treatment of COVID-19. All patients had laboratory-confirmed disease. Rectal and respiratory swabs were taken from all patients. Swabs taken on the same day were considered a “pair”. Researchers tested samples for severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2) RNA using quantitative reverse transcription polymerase reaction (RT-qPCR). Patients shown to be positive for fecal viral RNA were stratified based on duration of viral shedding (≤4 weeks vs 4 weeks). The researchers performed multivariable logistic regression to identify correlates of viral shedding duration.

In total, the researchers collected 1758 rectal swabs from 401 patients within 0-98 days of illness onset (median, 33 days). Overall, 80 patients (19.95%) tested positive for SARS-CoV-2 from rectal swab test. Rectal swab positivity was more common in pediatric patients compared with adults (56.67% vs 16.98%). When rectal samples were grouped by collection timepoint, viral RNA was present in 44.19%, 30%, 16.67%, 12.29%, 12.3%, 5.22%, and 0.76% of samples at weeks 1, 2, 3, 4, 5, 6, 7 since disease onset, respectively. After week 7, no samples were shown to be positive for fecal RNA. Demographic and clinical characteristics were similar between patients who were negative for SARS-CoV-2 viral RNA in the feces and patients who were positive. Paired respiratory samples were available for 80 patients who had positive fecal tests at any point. Of these patients, 58 (11.8%) pairs were double positive, 112 (21.7%) were positive in the rectal sample only, and 40 (7.7%) were positive for the respiratory sample only. The proportion of patients with higher viral loads in rectal vs respiratory samples increased with time since illness onset. Likewise, researchers concluded that fecal viral shedding tended to outlast respiratory shedding. Duration of fecal shedding was associated with higher neutrophil levels (OR, 1.549; 95% CI, 1.055-2.405; P =.034) and greater interval between illness onset and antiviral treatment (OR, 1.168; 95% CI, 1.011-2.369; P =.042). The longest observed period of prolonged fecal shedding was 43 days. RNA positivity was not associated with gastrointestinal symptom severity, suggesting that SARS-CoV2 may “use the intestine as a reservoir without altering…[function].”

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These study data suggest that SARS-CoV-2 RNA remains in fecal samples for a prolonged period of time after illness onset. Fecal samples had a higher viral load than paired respiratory samples, and typically remained positive for a longer duration of time. According to multivariable regression, early antiviral treatment administration may reduce SARS-CoV-2 persistence in the intestinal tract. “The gastrointestinal viral reservoir is potentially a long-lasting fomite for SARS-CoV-2 transmission even for asymptomatic patients,” researchers wrote. In order to avoid false negative test results, authors endorsed the use of viral diagnosis in stool specimens.  

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Zhao F, Yang Y, Wang Z, Li L, Liu L, Liu Y. The time sequences of oral and fecal viral shedding of coronavirus disease 2019 (COVID-19) patients [published online May 16, 2020]. Gastroenterology. doi: 10.1053/j.gastro.2020.05.035