Coughed up samples provide best rate of COVID-19 detection in tests, Boston study shows

BOSTON — A sample of phlegm coughed up by a test subject is the most accurate way of testing for COVID-19, according to new research published by researchers in Boston.

There are three primary ways people are tested for the presence of the coronavirus, through a nasal swab, a throat swab or through what is called sputum -- a substance coughed up by the test subject.

A team led by Dr. Jonathan Li, MD, a faculty member in the Division of Infectious Diseases at the Brigham, conducted a survey of test results. These studies included results from a total of 3,442 respiratory tract specimens.

The team looked at how often each collection method produced a positive result. For nasal swabs, the rate was 54 percent; for throat swabs, 43 percent; for sputum, 71 percent. The rate of viral detection was significantly higher in sputum than either swabs, the study reported. Detection rates were highest within one week of symptom onset for all three tests.

“The accurate diagnosis of COVID-19 has implications for health care, return-to-work, infection control and public health,” Dr. Li said. “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 with swab or sputum. From more than 1,000 studies, they identified 11 that met their criteria.

Not all patients are able to produce a sputum sample; for such patients, a nasopharyngeal swab may be the best collection method, the study noted.

“The holy grail will be to find a test that is readily acceptable by patients, easy to collect, and highly sensitive,” said Li.

This study was funded in part by the National Institutes of Health and the Harvard University for AIDS Research.

Abbvie and Jan Biotech both contributed to Li’s fees.

Paper cited: Li, Jonathan et al. “SARS-CoV-2 Detection in Different Respiratory Sites: a Systematic Review and Meta-Analysis” EBioMedicine DOI: xxx

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