Clinical pathology selected abstracts

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Editor: Deborah Sesok-Pizzini, MD, MBA, chief medical officer, Labcorp Diagnostics, Burlington, NC, and adjunct professor, Department of Clinical Pathology and Laboratory Medicine, Perelman School of Medicine, University of Pennsylvania, Philadelphia.

SARS-CoV-2 stool testing and potential for fecal-oral transmission of virus

February 2021—SARS-CoV-2 is transmitted through respiratory droplets, close person-to-person contact, and infected surfaces. Those with COVID-19 often present with fever and respiratory symptoms, and diagnosis relies on detecting the virus through specimens from the upper and lower respiratory tract. However, an increasing number of patients are exhibiting such gastrointestinal symptoms as diarrhea, vomiting, and abdominal pain. A growing number of studies are reporting the presence of SARS-CoV-2 RNA in stool samples and anal swabs, generating interest in research focused on a fecal-oral route of transmission. The authors conducted a study to assess the clinical relevance of testing stool samples and anal swabs for SARS-CoV-2 and to provide a critical overview of literature addressing possible fecal-oral transmission. They conducted a systematic literature search of articles from December 2019 to July 7, 2020. They then analyzed the data collected using descriptive statistics. The investigators included 95 studies in the qualitative analysis, in which 43 percent of the patients tested positive for SARS-CoV-2 in stool samples or anal swabs, with a positive test result up to 70 days after symptom onset. A meta-analysis performed on studies with at least 10 patients showed a pooled positive proportion of 51.8 percent. Sixty-four percent of patients with positive fecal samples remained positive for SARS-CoV-2 for a mean of 12.5 days and a maximum of 33 days after respiratory samples became negative for SARS-CoV-2. Of interest, the analysis showed that in 22 (one percent) patients, SARS-CoV-2 infection would not have been diagnosed without gastrointestinal specimen testing. The authors noted that in most studies for which serial measurements were performed, viral RNA was more likely to be detected in respiratory tract samples during an early stage of COVID-19, whereas GI specimens were more likely to be positive later in SARS-CoV-2–infected patients. The authors concluded that infection with SARS-CoV-2 does not necessarily imply that viable infectious virions are present in GI specimens or that the virus can be spread through fecal transmission. Additional studies using fresh stool samples at later time points would be needed to better determine the potential for fecal transmission. However, the study suggests that stool sample or anal swab testing should be considered when making decisions about patient care.

Van Doorn AS, Meijer B, Frampton CMA, et al. Systematic review with meta-analysis: SARS-CoV-2 stool testing and the potential for faecal-oral transmission. Aliment Pharmacol Ther. 2020;52:1276–1288.

Correspondence: Dr. Nanne K. H. de Boer at khn.deboer@amsterdamumc.nl

Saliva as an alternative to upper respiratory swabs for SARS-CoV-2 diagnosis

Quantitative reverse transcription PCR (qRT-PCR) is the diagnostic standard for SARS-CoV-2, the causative agent of COVID-19. The testing is typically performed by collecting an upper respiratory specimen using swabs. Among the drawbacks to swab sampling are the need for multiple samples, low sensitivity, and discomfort during sampling. Furthermore, shortages of swabs, transport media, and personal protective equipment limit the ability to conduct SARS-CoV-2 tests. Another form of testing for the virus involves saliva sampling, a noninvasive alternative to upper respiratory swabbing. The authors conducted a study to compare self-collected saliva samples with nasal and throat swab specimens collected by health care workers. They compared saliva samples with nasal and throat swab specimens from 110 patients with suspected SARS-CoV-2 infection from April through June 2020. The analysis was part of a prospective study conducted at Royal Liverpool University and Aintree University Hospitals. Most of the patients tested were hospitalized, and 19.1 percent were discharged directly from the emergency department. The analysis showed that 10.9 percent of saliva and 12.7 percent of nasal and throat swab specimens of the 110 paired samples tested positive for SARS-CoV-2 RNA. The viral loads for all samples ranged from 36 to 3.3 × 10⁶ copies/mL. The authors reported insignificant viral load discrepancies among all positive samples. Discrepancies found in two samples might have resulted from different processing times, which may reduce the stability of RNA. The authors found that saliva sampling can improve SARS-CoV-2 diagnostic techniques and that saliva samples were easier to collect than nasal and throat samples and do not require sampling proficiency. However, the study focused on hospitalized patients, so additional studies are needed for patients with mild and asymptomatic SARS-CoV-2 infection. The authors also suggested that more research is needed to document the effects of storage and transport on RNA and viral loads. They concluded that as rates of SARS-CoV-2 infection increase, it is important to look at the ease and effectiveness of performing diagnostic techniques in clinical laboratories.