26 Jul Sputum Sampling Most Sensitive For COVID, the Earlier the Better
MedicalResearch.com Interview with:
Jonathan Li, MD MMSc
Assistant Professor of Medicine
Harvard Medical School
Division of Infectious Diseases
Brigham and Women’s Hospital
MedicalResearch.com: Why did you do this study?
Response: The accurate diagnosis of COVID-19 is critical for our patients in order to receive appropriate care, and for infection control and public health. In the US, the gold standard for COVID diagnosis is sampling through a nasopharyngeal swab (NP) but is that really the best way to diagnose COVID? As many of your viewers may have experienced first hand, nasopharyngeal swabs require inserting a long swab into the back of the nose, which is incredibly uncomfortable for the patient, technically-challenging for the health care worker, and requires equipment and reagents that are in short supply. There are also alternative sampling methods for COVID diagnosis.
In Asia, oropharyngeal sampling(OP), or swabbing the back of the mouth, are commonly used and in my hospital, the Brigham and Women’s Hospital, we frequently test sputum as well for inpatients. But there’s a lot of confusion in the field about which of these methods is the most sensitive?
We undertook this study to try to bring some clarity to this question of what is the most sensitive way to diagnose COVID and detect SARS-CoV-2?
MedicalResearch.com: What did you do and find?
Response: We performed an exhaustive review of the literature and aggregated data from over 3000 NP swabs, OP swabs, and sputum samples. We also looked whether the timing of sampling affected the tests. The results were fairly clear – compared to our standard NP swab, OP swab was not as good, but sputum sampling was better and showed higher sensitivity in detecting the virus. In addition, we found that the earlier a patient was tested, the better. Regardless of which sampling site, the sensitivity of the test was best in the first week after symptoms started.
MedicalResearch.com: What are the limitations?
Response: Not all patients may be able to produce sputum and in those patients, NP swabs are still going to be the best bet. The patients included in this study were likely on the sicker end of the spectrum and additional studies are needed of patients who are asymptomatic or have mild symptoms. There are also a number of alternative sampling methods that people are using, including anterior nasal swabs and saliva, which will require more validation.
MedicalResearch.com: How should this change the way we test for COVID?
Response: The holy grail is to find a test that is readily acceptable by patients, easy to collect, and highly sensitive. We think that using sputum moves us one step closer to that scenario. At the BWH, clinicians can order a test sputum COVID test and this data validates that approach and suggests that for the sicker patients, sputum may be a better way to test and monitor patients. In the end, we need to do everything we can to lower the barriers to testing and I think that sputum testing can do that by making it easier for our patients and avoiding the need for swab supplies that are becoming more difficult to obtain
Abbas Mohammadi, Elmira Esmaeilzadeh, Yijia Li, Ronald J. Bosch, Jonathan Z. Li. SARS-CoV-2 detection in different respiratory sites: A systematic review and meta-analysis. EBioMedicine, 2020; 102903 DOI: 10.1016/j.ebiom.2020.102903
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