Rapid antigen test with phlegm is more sensitive and detects SARS-CoV-2
earlier than with nasal swab
Abstract
Omicron is the current variant of SARS-CoV-2. It has high
transmissibility and evades human immunity. Early and accurate diagnosis
is essential for therapy, prognosis, and curbing the spread of the
virus. Here we reported a new sampling method for the rapid antigen
test, with specimens from phlegm, instead of from nasal swabs.
Sensitivities in detection of SARS-CoV-2 antigen were compared within
the two specimens, and between rapid antigen tests with phlegm specimens
and PCR tests. Of 41 volunteers, thirty-one with positive phlegm
specimens of SARS-CoV-2 eventually had typical COVID-19 symptoms, which
suggested rapid antigen tests with phlegm specimens had 100 % accuracy.
Fourteen of these had antigen tests with nasal swab specimens: 13
negative and 1 positive. Combined with that the antigen levels of the
6561-fold diluted phlegm specimen were comparable to those of the
original nasal swab specimen, antigen tests with phlegm specimens are
more sensitive and earlier detect SARS-CoV-2 than with nasal swab
specimens. Interestingly, case studies indicated antigen tests with
phlegm specimens earlier notified patients of positive infection than
PCR tests. Phlegm specimens enhanced sensitivity in detection of
SARS-CoV-2 in antigen tests, resulting in earlier diagnosis (12 to 42
hours, n=6) than nasal swab specimens. The sensitivity of antigen tests
with phlegm specimens is comparable to that of PCR tests, but the former
earlier outputs test results. Rapid antigen tests with phlegm specimens
facilitate monitoring the health of COVID-19 patients and direct
recovery.