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SARS-CoV-2: Throat samples can detect better than nasal specimens

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Testing oropharyngeal secretions for SARS-CoV-2 resulted in fewer false-negative results among patients who seemed to have recovered from the infection, compared with nasal-sample testing, according to a study published in the Journal of Dental Research.

Although using
oropharyngeal secretions improved nucleic acid amplification testing for the
novel coronavirus, it should only be considered a surrogate for potential
transmissibility. Cultures of diseases that spread through aerosols such as
SARS-CoV-2 can only be tested accurately in a biosafety level 3 microbiology
laboratory, according to the authors. Dentists, like those in North
Carolina
, who were given the greenlight to administer tests that
detect COVID-19, may want to consider the type of test they choose to use.

“Detection of
viral RNA from a patient’s secretions is not confirmative of viral
infectivity,” wrote the authors, led by Jingzhi Ma, DDS, PhD, of Huazhong
University of Science and Technology in Wuhan, China.

A continuing threat to
public health

Worldwide, there have
been more than 11.5 million confirmed cases of COVID-19, including about
536,000, deaths reported to the World Health Organization. In addition to
recent surges in countries including the U.S., officials must also contend with
those patients who have seemingly recovered from the virus and been discharged
from hospitals only to test positive again later.

Recurrent positive
cases impede medical communities, health departments, and governing officials
from managing COVID-19 effectively. Relatively high rates of false-negative
results obtained from nucleic acid amplification testing via reverse
transcription polymerase chain reaction tests, which have sensitivity levels of
66% to 80%, may partially contribute to the issue.

The accuracy of
nucleic acid amplification testing is crucial for determining whether an
individual should be discharged; a patient must obtain two negative results
from this type of testing performed 24 hours apart before he or she can be
discharged. Recent evidence has shown that more SARS-CoV-2 can be found in
oropharyngeal than in nasopharynx secretions, so the authors opted to compare
the two methods performed in nucleic acid amplification testing.

The first study
included 75 COVID-19 patients who were set to be discharged and tested negative
using two consecutive nucleic acid amplification tests of viral samples
retrieved with nasopharyngeal swabs. Potential false-negatives were detected in
the first group, so oropharyngeal secretion and nasopharynx secretion samples
were collected from 50 additional COVID-19 recruits who were in recovery for a
second prospective study. The researchers compared the diagnostic value of the
two viral RNA sampling methods.

Oropharyngeal
secretions obtained from two of the 75 subjects in the first study yielded
positive results for SARS-CoV-2. In the second study, oropharyngeal secretion
samples were significantly more sensitive for detecting the virus than samples
taken from the nose. Samples taken from the throat missed only 14% of positive
cases, whereas those taken from the nose missed 59%, according to the authors.

A link in the chain

The study was not
without limitations, including measurement of the specificity of tests. Also
known as the true-negative rate, specificity refers to the proportion of actual
negatives that are correctly identified as testing negative for a disease.
Nucleic acid detection of SARS-CoV-2, which currently is not available, is
necessary to express specificity accurately. Also, the study had a small sample
size, they wrote.

“Results of the
present study are supportive of the notion that [oropharyngeal secretion]
sampling improves the accuracy of SARS-CoV-2 nucleic acid testing,” the
authors concluded.

-Courtesy by Dr Biscupsid


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