Respiratory Sampling Strategies for Detecting SARS-CoV-2 Compared

Sputum sampling was found to be a valuable method for diagnosing and monitoring patients with coronavirus disease 2019 (COVID-19), according to a recent systematic review and meta-analysis published in EBioMedicine.

Currently, the most commonly used method of specimen collection for the diagnosis of COVID-19 is through the use of nasopharyngeal (NP) swabs. However, this method has several drawbacks, such as being technically challenging and uncomfortable for patients. The procedure is also associated with frequent coughing and sneezing, which may put healthcare providers at increased risk.

In this analysis, investigators at Brigham and Women’s Hospital aimed to compare different respiratory sampling strategies used to detect the RNA of the virus that causes COVID-19, severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2). These sampling strategies included oropharyngeal swab, sputum sampling, and NP swab. Eleven studies that assessed ≥2 respiratory sampling sites in COVID-19 patients were included in the analysis. A total of 3442 respiratory tract specimens were analyzed in the review.

“Compared to nasopharyngeal swab sampling, sputum testing resulted in significantly higher rates of SARS-CoV-2 RNA detection while oropharyngeal swab testing had lower rates of viral RNA detection,” the study authors stated. Estimated percentages of positive samples were reported to be 43% (95% CI, 34-52) for oropharyngeal swabs, 54% (95% CI, 41-67) for NP swabs, and 71% (95% CI, 61-80) for sputum sampling.

Additionally, findings of the analysis revealed an association between earlier sampling following symptom onset and improved detection rates, with the highest detection rates occurring within 1 week of symptom onset for all 3 collection methods.

“In summary, this systematic review and meta-analysis demonstrates that compared to nasopharyngeal swab sampling, sputum testing resulted in significantly higher rates of SARS-CoV-2 RNA detection while oropharyngeal swab testing had lower rates of viral RNA detection,” the study authors concluded. They added, “Earlier sampling after symptom onset was associated with improved detection rates, but the differences in SARS-CoV-2 RNA detection was consistent between sampling strategies regardless of the duration of symptoms.”

References:

1. Mohammadi A, Esmaeilzadeh E, Li Y, Bosch RJ, Li JZ. SARS-CoV-2 detection in different respiratory sites: A systematic review and meta-analysis. EBioMedicine. 2020; 102903. doi: 10.1016/j.ebiom.2020.102903.
2. Sputum testing provides higher rate of COVID-19 detection. https://www.eurekalert.org/pub_releases/2020-07/bawh-stp072420.php