Virus World

Saliva Specimens to Detect SARS-CoV-2 Infection In this letter, the investigators report that saliva specimens and nasopharyngeal swab specimens had similar sensitivity in the detection of COVID-19.  Rapid and accurate diagnostic tests are essential for controlling the ongoing Covid-19 pandemic. Although the current standard involves testing of nasopharyngeal swab specimens by quantitative reverse-transcriptase polymerase chain reaction (RT-qPCR) to detect SARS-CoV-2, saliva specimens may be an alternative diagnostic sample. Rigorous evaluation is needed to determine how saliva specimens compare with nasopharyngeal swab specimens with respect to sensitivity in detection of SARS-CoV-2 during the course of infection. 

A total of 70 inpatients with Covid-19 provided written informed consent to participate in our study available with the full text of this letter at NEJM.org). After Covid-19 was confirmed with a positive nasopharyngeal swab specimen at hospital admission, we obtained additional samples from the patients during hospitalization. We tested saliva specimens collected by the patients themselves and nasopharyngeal swabs collected from the patients at the same time point by health care workers. Using primer sequences from the Centers for Disease Control and Prevention, we detected more SARS-CoV-2 RNA copies in the saliva specimens (mean log copies per milliliter, 5.58; 95% confidence interval [CI], 5.09 to 6.07) than in the nasopharyngeal swab specimens (mean log copies per milliliter, 4.93; 95% CI, 4.53 to 5.33).  In addition, a higher percentage of saliva samples than nasopharyngeal swab samples were positive up to 10 days after the Covid-19 diagnosis. At 1 to 5 days after diagnosis, 81% (95% CI, 71 to 96) of the saliva samples were positive, as compared with 71% (95% CI, 67 to 94) of the nasopharyngeal swab specimens. These findings suggest that saliva specimens and nasopharyngeal swab specimens have at least similar sensitivity in the detection of SARS-CoV-2 during the course of hospitalization...

Published in New England J. Medicine (August 28, 2020):

https://doi.org/10.1056/NEJMc2016359

Early and accurate detection is critical for preventing the spread of COVID-19 and providing appropriate care for patients. Nasopharyngeal (NP) swabs, which require inserting a long shaft into the nasal cavity to collect a sample from the back of the nose and throat, are currently the gold standard for collecting a specimen for diagnosis. But the procedure is technically challenging, often uncomfortable for patients and requires personal protective equipment that may be in short supply. Other approaches to collecting specimens—including from an oropharyngeal swab and sputum—have been tested in small studies, but there is uncertainty about which method is best for detecting the virus. In a new study published in EBioMedicine, investigators from Brigham and Women's Hospital conducted a systematic review and meta-analysis, analyzing data from more than 3,000 specimens to compare the three approaches. The team found that sputum testing detected the RNA of the virus that causes COVID-19 at significantly higher rates while oropharyngeal swab testing had lower rates. Regardless of the collection method, the earlier samples were collected after symptoms began, the higher the detection rate.

"The accurate diagnosis of COVID-19 has implications for health care, return-to-work, infection control and public health," said corresponding author Jonathan Li, MD, a faculty member in the Division of Infectious Diseases at the Brigham. "Our gold standard in and out of the hospital is the nasopharyngeal swab, but there's a lot of confusion about which sampling modality is best and most sensitive. Our study shows that sputum testing resulted in significantly higher rates of SARS-CoV-2 detection and supports the use of this type of testing as a valuable method for the diagnosis and monitoring of COVID-19 patients." Li and his colleagues scoured the literature—both preprints and published papers—for studies that assessed at least two respiratory sampling sites using an NP swab, oropharyngeal swab or sputum. From more than 1,000 studies, they identified 11 that met their criteria. These studies included results from a total of 3,442 respiratory tract specimens. The team examined how often each collection method produced a positive result. For NP swabs, the rate was 54 percent; for oropharyngeal swabs, 43 percent; for sputum, 71 percent. The rate of viral detection was significantly higher in sputum than either oropharyngeal swabs or NP swabs. Detection rates were highest within one week of symptom onset for all three tests.

Study Published in EbioMedicine (July 18, 2020):

https://doi.org/10.1016/j.ebiom.2020.102903