In a new review study, researchers compared different COVID-19 tests and found that sputum testing detected the RNA of the virus that causes COVID-19 at much higher rates while oropharyngeal swab testing had lower rates.
The research was conducted by a team from Brigham and Women’s Hospital.
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 the study, the team did a systematic review and meta-analysis, analyzing data from more than 3,000 specimens to compare the three approaches.
Regardless of the collection method, the earlier samples were collected after symptoms began, the higher the detection rate.
The team examined how often each collection method produced a positive result. For NP swabs, the rate was 54%; for oropharyngeal swabs, 43%; for sputum, 71%.
The rate of viral detection was much higher in sputum than either oropharyngeal swabs or NP swabs. Detection rates were highest within one week of symptom onset for all three tests.
The findings showed that sputum testing resulted in much higher rates of SARS-CoV-2 detection and supported the use of this type of testing as a valuable method for the diagnosis and monitoring of COVID-19 patients.
The team says when it comes to testing, the earlier the better, as diagnostic accuracy is improved earlier after symptom onset, regardless of the sampling site.
Unlike antibody testing, it’s very rare to have a false positive qPCR test when diagnosing COVID-19 early in the course of the disease using these methods
Nasopharyngeal swabs are collected through the nasal cavity; oropharyngeal swabs are collected by inserting a shaft through the mouth, and sputum samples are generally collected by having a patient cough deeply to produce and expel phlegm.
Not all patients are able to produce a sputum sample; for such patients, a nasopharyngeal swab may be the best collection method.
The team says the holy grail will be to find a test that is readily acceptable by patients, easy to collect, and highly sensitive.
One author of the study is Jonathan Li, MD, a faculty member in the Division of Infectious Diseases at the Brigham.
The study is published in EBioMedicine.
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