DISCUSSION
Early and accurate diagnostic
tests are essential to curb the spread of SARS-CoV-2 and control the
ongoing COVID-19 pandemic. Since the current variant of the SARS-CoV-2
virus has high transmissibility and evades human immunity, it is urgent
to determine whether one is infected by SARS-CoV-2 who has some early
common COVID-19 symptoms such as cough, low fever, and headache. Early
and accurate detection helps patients to adjust their lifestyle by
increasing sleep, stopping alcohol and smoking, separating them from
young or old family members or members having basic diseases, and
storing some required foods and medicines for recovery time. Considering
the reduction of available nuclei acid test sites and cross infections
by other positive patients, people tend to have a self-test with rapid
SARS-CoV-2 antigen test with nasal swab specimens at home to know
whether they are infected.
PCR test has been a gold standard to diagnose SARS-CoV-2 infection
because of its sensitivity. However, it has shortcomings such as false
negative results, crossing infections, long procedure time, and
professional personnel and instrument involvement. As a substitutive
test, rapid SARS-CoV-2 antigen tests are carried out using a specimen of
nasal swabs. The rapid antigen test has several advantages such as high
accuracy, portable use, and no requirement for professional background.
However, the essential shortcoming is the low sensitivity in detection
of SARS-CoV-2 compared to the PCR test. Currently, our research updated
the collection method of specimens and used phlegm samples for rapid
SARS-CoV-2 antigen tests. Using this new sampling method, we
demonstrated the sensitivity in detection of SARS-CoV-2 in rapid antigen
tests is about 6000-fold higher than that using nasal swab specimens.
Importantly this sensitivity enhancement of rapid antigen tests with
phlegm specimens made it comparable to PCR tests for diagnosing
SARS-CoV-2 infection. Two reasons possibly contribute to the elevated
sensitivity. First, the common symptom caused by the omicron variant of
SARS-CoV-2 is sore throat suggesting virus titer is high in throat
secretion; Second, more viruses are picked in the tests by dipping
phlegm.
Using the rapid antigen test with phlegm specimens, from 41 volunteers
we diagnosed 31 positive cases of SARS-CoV-2 infection, and these cases
all developed as typical COVID-19 suggesting the method has 100%
accuracy. Thirteen cases showed negative rapid antigen tests with nasal
swab specimens but positive phlegm specimens, indicating rapid antigen
tests with phlegm specimens can earlier detect SARS-CoV-2 infection
cases than with nasal swab specimens. From 6 cases, we found the
advanced time by rapid antigen test with phlegm specimens is about 12-42
hours compared to the tests with nasal swab specimens (Figure 1-4). The
advanced time is a big window for patients to arrange the following plan
and prevent their family members from further infection, and for
physicians to start specific therapy against severe symptoms at the
early stage of COVID-19 development. Even though the antigen test with
phlegm specimens and the PCR test detected SARS-CoV-2 at the same time,
technically the former test notified of the output result
~10 hours earlier than the latter one (Figure 3, 4).
During recovery from COVID-19, antigen tests with phlegm specimens
better determine a negative time, which is comparable to PCR tests
(Figure 5). It helps patients to wisely make decisions for recovery
avoiding the side effects of improper treatments. Taken together,
antigen tests with phlegm specimens accurately and early detect
SARS-CoV2, and better determine the recovery time suggesting a good aid
to monitor the health conditions of COVID-19 patients.