Keywords COVID-19 - SARS-CoV-2 - rapid antigen test - nasopharyngeal - nonrespiratory samples
Introduction
A novel human pathogen emerged at the end of 2019 at the city of Wuhan, China and
is now known as severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2), causing
the coronavirus disease 2019 (COVID-19).[1 ] In COVID-19, fever is usually the first symptom with subsequent development of respiratory
symptoms.[2 ]
[3 ] Most patients with COVID-19 experience a mild disease course; albeit, approximately
20% develop severe disease with high mortality rate.[2 ]
[3 ]
Laboratory diagnosis and management of COVID-19 has been helpful in combating the
spread of SARS-CoV-2. At present, the gold standard for COVID-19 diagnosis is reverse
transcription-quantitative polymerase chain reaction (RT-qPCR) which uses nasopharyngeal
swabs, throat swabs, or saliva samples.[4 ] RT-qPCR kits that do not require viral ribonucleic acid (RNA) extraction and high-throughput
RT-qPCR systems have also been developed. Although such tests are widely utilized
in tertiary care centers and large well-equipped hospitals, they are rarely available
in the local clinics which are more approachable for the patients who are under suspicion.
Studies done on rapid antigen tests (RATs) have shown sensitivity of 61.70% and specificity
of 98.26% for diagnosis of COVID-19.[5 ] In the present study, we have used RAT to detect SARS-CoV-2 antigen in samples other
than nasopharyngeal.
Material and Methods
This descriptive study was done at a single center dedicated for COVID-19 patients
in a tertiary care center in North India. RAT was done on samples like ascitic fluid,
pleural fluid, drain fluid, bile, bronchoalveolar lavage (BAL), cerebrospinal fluid,
endotracheal tube aspirate (ETA), sputum, tissue, and urine, which were sent to the
microbiology laboratory for culture and sensitivity testing. The RAT was done according
to the kit insert provided by the STANDARD Q COVID-19 antigen test which is ideally
for testing nasopharyngeal sample. Samples were used directly without any dilution.
Test was performed as soon as the sample was received and result noted within 30 minutes
of the test.
Ethical Approval
Since the samples consisted of routine samples for culture, ethical consent was not
taken. However, a blanket ethical clearance for evaluation of all COVID antigen kits
was obtained having the ethical committee approval number IEC 668/ July 3, 2020.
Result
A total of 150 patients were included in the study admitted in the hospital. Out of
150 patients, 88 (58.66%) were male and 62 (41.33%) were female. Patients before admission
were confirmed as having COVID-19 disease by RT-PCR (73), Truenat Beta (14), Xpert
(20), antigen test (17), Xpert and antigen (1), RT-PCR and antigen (6), Truenat and
RT-PCR (17), and Xpert and RT-PCR (2). Samples other than nasopharyngeal swab collection
were tested. [Table 1 ] shows the distribution of sample and their test results. Eleven (7.33%) samples
were positive and 138 (92.66%) were negative for the test. Out of the 11 specimens
which were positive for the antigen test, 7 were respiratory, 3 were fluid, and 1
was bile. The duration of illness was 6.2 days (95% CI: 3.6–8.7) for the majority
of patients with positive specimens. Exceptions were there as for one sample (BAL)
test was positive after 2 weeks of onset of symptoms and for another (sputum) patient
was asymptomatic. [Fig. 1 ] shows the time interval for each positive sample depicting starting of symptoms
to the test.
Fig. 1 Time interval from symptoms to the test (days).
Table 1
Clinical samples with severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2)
antigen test results
Samples
Antigen test
positive/negative
Total
Ascitic fluid
2/11
13
Drain fluid
1/6
7
Pleural fluid
0/4
4
Cerebrospinal fluid
0/6
6
Bile
1/3
4
Urine
0/74
74
Tissue
0/1
1
Sputum
1/6
7
Endotracheal aspirate
4/26
30
Bronchoalveolar lavage
2/2
4
Total
11/139
150
Discussion
Since the outbreak of COVID-19, various strategies are being tried, tested, and followed
for the rapid detection, treatment, and containment of this disease. Many have lost
their life due to this pandemic. Globally, 101,636,470 have been infected and 2,194,790
have died.[6 ]
In our country, till now 10,727,240 have suffered and 154,069 have succumbed to this
disease.[6 ] As far as diagnostics is considered, at present rRT-PCR is considered the gold standard.
To minimize infrastructure cost, various other modes of nucleic acid detection modalities
like Truenat and CBNAAT are also in use. Antigen testing with high specificity[5 ] has also helped in rapid detection, isolation, and treatment of individuals suspected
of having COVID-19. RATs for SARS-CoV-2 are being usually done in throat and nasopharyngeal
sample. In a study done in Japan, samples other than nasopharyngeal and throat were
also tested with RT-PCR and four different kits of rapid antigen for SARS-CoV-2 were
evaluated.[6 ] Sample tested were gargle lavage, saliva, throat swab, nasal vestibule swab, nasopharyngeal,
sputum, and tracheal aspirate. Swabs were transported in BD universal viral transport
medium; saliva, sputum, and tracheal aspirate samples were diluted in BD universal
viral transport medium if needed and were used as test specimens. Gargle lavages were
tested directly. Among the four antigen test kits, one kit was same as what we had
used. That kit was able to identify SARS-CoV-2 antigen in saliva (10/27), nasopharyngeal
swab (8/18), sputum (1/4), and tracheal aspirate (7/17). In our study, the kit detected
the antigen in endotracheal aspirate (4/29), BAL (2/4), sputum (1/7), ascitic fluid
(2/13), drain fluid (1/7), and bile (1/4).
With regard to detection of SARS-CoV-2 in nonrespiratory samples, studies have shown
its presence in various nonrespiratory samples. RT-PCR has detected SARS-CoV-2 RNA
in stool sample in many studies.[7 ]
[8 ]
[9 ]
[10 ]
[11 ]
[12 ] In some studies, where serum or blood were tested, the viral RNA was detected in
30 to 87.5% of patients with COVID-19. The viral RNA shedding was for longer duration
in intensive care unit patients (14.63 ± 5.88 days standard deviation [SD]) compared
with non-ICU patients (10.17 ± 6.13 days SD).[13 ]
[14 ]
[15 ]
[16 ] This viral RNA has also been detected in ocular tissue too.[17 ] Ours is a novel study on antigen detection on samples other than nasopharyngeal
with positivity of 7.33%. Our study shows that viral antigen and therefore the virus
may be present in many other organs apart from the respiratory tract.
Conclusion
The COVID-19 antigen test kit, though dedicated for nasopharyngeal samples was able
to detect presence of antigen in other clinical samples. The sample infectivity and
transmissibility albeit cannot be assessed with this test alone.
