COVID-19 Resource Center
COVID-19 Resource Center
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Disclosures: The authors report no relevant financial disclosures.
August 17, 2020
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Study shows drawbacks of deep-throat saliva for COVID-19 testing

Source/Disclosures
Disclosures: The authors report no relevant financial disclosures.
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Deep-throat saliva, although advantageous for COVID-19 testing because it is self-collected, is suboptimal in sensitivity compared with sputum and pooled nasopharyngeal and throat swabs, according to study data.

In several countries, including the United States and South Korea, well-protected health care workers collect nasopharynx plus throat swabs from passengers at drive-through testing sites, Paul K.S. Chan, MBBS, MSc, MD, professor of microbiology at the Chinese University of Hong Kong, and colleagues noted. However, Hong Kong “has adapted an alternate approach of home-based screening” that uses self-collected deep-throat sputum, the wrote.

Paul K.S. Chan

Deep-throat saliva is the specimen type of choice by the Hong Kong government to screen for COVID-19 cases in the community,” Chan told Healio. “Deep-throat saliva has an advantage of being self-collected, thus avoiding infectious exposure to health care workers. However, its performance, especially sensitivity, has not been properly evaluated. If the false-negative rate is high, it could create false reassurance and inadvertent spread in the community.”

Chan and colleagues conducted a prospective study in two regional Hong Kong hospitals during which they examined 563 serial samples collected during the virus shedding periods of 50 patients 150 deep-throat saliva (DTS) samples, 309 pooled-nasopharyngeal (NP) samples and throat swabs, and 104 sputum samples.

According to the study, DTS had the lowest overall RT-PCR positive rate (68.7% vs. 89.4% for sputum samples and 80.9% for NP and throat swabs), as well as the lowest viral RNA concentration (mean log copy/mL 3.54 vs. 5.03 for sputum samples and 4.63 for NP and throat swabs). They found that analyses with respect to time from symptom onset and severity yielded similar results.

Chan and colleagues estimated that the overall false-negative rate of DTS could be 31.3% and that the false-negative rate of non-sputum producers was 2.6 times higher than that of sputum producers.

“Persons receiving [a] deep-throat saliva test should be reminded of the possibility of false-negative results and remain vigilant to minimize transmission to others. If deep-throat saliva is used, public health strategy to cover the expected proportion of false-negatives is needed,” Chan said. “Whenever feasible, it is advisable to replace deep-throat saliva with specimens of higher diagnostic yield, eg, sputum, nasopharyngeal or throat swabs.”