In the above cases, all patients are medically stable after more than 10 days of hospitalization for medical antiviral treatment. The patients recovered well as the vital signs back to normal ranges, categorized as cured patients according to the current clinic guidelines. However, the viral nucleic acid test is still positive in the fecal specimens, despite repeated negative results observed in the specimens of respiratory secretions. We noticed this discrepancy in multiple cases with diverse clinical backgrounds, independent of genders, age ranges, and clinical backgrounds. To be pointed out, no patient in our study demonstrated gastrointestinal symptoms. It is worth to be noted that for the patient of case 2, three consecutive negative results in nasopharyngeal swabs were observed with 24-hour intervals, which satisfied the discharge standards stipulated by the Novel Coronavirus Pneumonia Prevention and Control guideline issued by the Chinese National Health Committee [4]. However, the strong positive result (lower Ct values) of viral RNA in the fecal specimens suggested the existence of viable virions with the patients, implying highly infectious and transmissible capabilities.
During the preparation of our manuscripts, two independent clinic reports demonstrated the detection of viral RNA by RT-PCR with rectal swabs after nasopharyngeal testing turn negative [7, 8]. It was then proposed that the gastrointestinal tract may shed virus and fecal-oral transmission may be possible, although in vivo infection evidence was not provided to show that the virus in the fecal samples is transmissible. In our study, the prolonged duration of viral RNA in the stool specimens of the patients can last for more than 20 days after hospitalization for medical treatments, and more than 8 days after free of the virus in the respiratory specimens (Table 1, case 1). Generally, it is unexpected that the viral RNA could exist for such a long time without the protection of active virions in the environment.
Our findings recommended that clinicians should pay more attention to the negative result of the viral nucleic acid tests when evaluating the treatment effect and discharge of the patients. Parallel tests should be conducted with different types of specimens to make the evaluation or assessments accurate, such as saliva, sputum, alveolar lavage fluid, feces, etc. Also, we proposed that viral nucleic acid tests of fecal specimens should be included in the screening of suspected patients and more precaution procedures were necessary for the medical care providers.
Molecular assays such as RT-PCR can detect viral RNA for a longer duration than other biochemical tests (e.g., antigen detection diagnostic tests). However, our clinical findings reinforced the concern that although molecular assays have high sensitivities, negative molecular assay results may not always exclude a diagnosis of infection, such as the negative respiratory specimens we reported here. The reasons underlying this issue is complicated, but it is plausible to propose that new criteria, in this scenario, need to be integrated for a comprehensive evaluation of the discharge of the patient and the cure of the disease. Moreover, strict hygiene or sanitation precautions are required during the hospitalization or quarantine, considering the extra-pulmonary viral shedding in COVID–19 patients.
There are many unknown features for the novel coronavirus outbreak in 2019. Investigations are underway to better understand transmission dynamics, epidemiological and clinical characteristics of the illness [9]. We will continue to track viral nucleic acid tests of fecal and other specimens in more patients, as well as in the hospital environment, and try to reveal the associations between the presence of virions with clinical features of this emerging disease. The cell culture on positive stool PCR samples is also proposed to be conducted to prove that the virus is viable and transmissible.