FIGURE LEGENDS
Figure 1. Rapid antigen test with phlegm specimens is more sensitive than that with nasal swab specimens. (A) A patient with mild symptoms of COVID-19 volunteered simultaneously for rapid antigen tests with both phlegm and nasal swab specimens. Viral antigens of phlegm liquids from the deep throat or specimens from the nostril were extracted with antigen extraction buffer from a rapid antigen test kit. Three drops of extracted antigen were applied for tests. Test time 0 h indicated when the phlegm specimen was initially positive, and 12 h was the passed time after the phlegm specimen was positive; (B) The phlegm sample was consecutively diluted at 3-fold for a test of sensitivity in detection of SARS-CoV-2. Sixty microliters of the original or diluted sample were applied for rapid antigen tests. SARS-CoV-2 antigen was still detectable in the 2187-fold diluted phlegm. The antigen levels in the 6561-fold diluted phlegm sample are comparable to that in the nasal swab sample indicated in rapid SARS-CoV-2 antigen tests. Control is the antigen extraction buffer only.
Figure 2. The time to detect SARS-CoV-2 in antigen tests with phlegm specimens is earlier than with nasal swab specimens. (A) In patient 1, the SARS-CoV-2 antigen in the phlegm specimen was not detectable on Day 0 and was detected on the next day (Day 1, 0 h). SARS-CoV-2 antigen in the nasal swab specimen was not detectable at the beginning of Day 1 (0 h), but detected 13 hours after the phlegm specimen was positive on the same day (13 h); (B) In patient 2, on Day 1, SARS-CoV-2 antigen was detected in phlegm specimens (0 h and 13 h). In nasal swab specimens, antigen was not detected (0 h, 13 h) till Day 2 (24 h) and the relative intensity of the “T” band was stronger after 35 hours (35 h); (C) In patient 3, SARS-CoV-2 antigen was detected in the phlegm specimen on Day 1 (0 h), but not detected in nasal swab specimens until 42 hours later on Day 3 (42 h). The yellow triangle indicates the time when the SARS-CoV-2 antigen was initially detected in the phlegm specimen; The blue triangle stands for the time point when the antigen was initially detected in the nasal swab specimen.
Figure 3. The rapid antigen test with phlegm specimens notified the patient of SARS-CoV-2 infection earlier than the PCR test.A patient was exposed to a positive case of COVID-19 and collected specimens for viral detection. On Day 0 , a phlegm specimen was collected for a rapid antigen test, and the nucleic acid specimen was collected for a PCR test (the result was notified on Day 1). Both tests showed negative results. On Day 1 , both phlegm and nasal swab (N. Swab) specimens were tested for rapid SARS-CoV-2 antigen as indicated. Viral antigens in the phlegm specimen were detected (0 h), and a nucleic acid specimen was collected for a PCR test, with notification of the positive nucleic acid specimen 11 hours after the phlegm sample was positive (11 h). On Day 2, SARS-CoV-2 antigens from the nasal swab specimen were detected, 35.5 hours after positive phlegm was determined (35.5 h). The yellow or blue triangle indicates the time when SARS-CoV-2 antigens were detected in phlegm or nasal swab specimen respectively. The green or red triangle designates the time when the results of a PCR test of SARS-CoV-2 RNA were notified.
Figure 4. Rapid antigen test with phlegm specimen facilitates monitoring the health of COVID-19 patients. On Day 1 , a tiny amount of SARS-CoV-2 antigen was detected at a weak band in phlegm (0 h), and the nucleic acid specimen was collected for PCR test on the same day. On Day 2 , the patient was notified of the positive nucleic acid sample 10 hours later than the first positive phlegm specimen, and the specimen of the nasal swab in antigen test was detected 21 hours after the first positive phlegm specimen (21 h). The patient had no symptoms until the nasal swab specimen was positive 21 hours after the first positive phlegm specimen. The patient had a slight cough, and an increase in body temperature 29 hours post the first positive phlegm specimen. The yellow, blue, or red triangle indicates the time when SARS-CoV-2 was initially detected in the phlegm specimen, the nasal swab specimen, or the nucleic acid sample by a PCR test (time with the notified result) respectively.
Figure 5. Rapid antigen tests with phlegm specimens can be used to direct recovery. Day 9 - 12 is the 9th – 12th day after the first positive phlegm specimen.(A) On Days 9 – 11, the nasal swab specimens of Patient 1 were negative but the phlegm specimens were still positive, indicating a rapid antigen test with phlegm specimens more accurately showed the patient’s infection condition. On Day 12, both specimens were negative;(B) On Day 9, both the phlegm and the nucleic acid samples of Patient 2 were still positive, but the nasal swab specimen by an antigen test was negative. On Day 10, both the PCR test and the phlegm antigen test showed negative results. The red or green triangle designates the time when SARS-CoV-2 nucleic acid specimens were collected and tested as positive or negative in PCR tests; (C) On Day 11, the phlegm specimen of Patient 3 was positive but the nasal swab one was negative. On Day 12 both antigen specimens and the nucleic acid sample with PCR test became negative in SARS-CoV-2 detection, suggesting the rapid antigen test with phlegm was comparable to the PCR test directing recovery from COVID-19.