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Evaluation of Rapid Antigen Tests Using Nasal Samples to Diagnose SARS-CoV-2 in Symptomatic Patients
Introduction
Since December 2019, the number of Coronavirus disease 2019 (COVID-19) confirmed cases has been rising rapidly despite the efforts to limit its spread (1, 2). The World Health Organization (WHO) declared COVID-19 to be a pandemic on March 12, 2020 (2). To date, the total number of cases worldwide has exceeded 120 million, with over 2.5 million deaths (3). The National COVID-19 Taskforce in Bahrain has been working diligently to confine this disease’s spread since the start of the pandemic. Bahrain has had more than 140,000 COVID-19 cases, afflicting about 8% of the population (4).
One of the most effective ways to mitigate a viral outbreak in the absence of population-wide vaccination is the efficient detection of cases early enough to take the necessary precautions that could halt its spread to contacts and allow for the adequate management of high-risk patients. However, this is difficult to achieve in the absence of a readily available, rapid, and cost-effective test with sufficiently high specificity and sensitivity for early detection of COVID-19 infected patients in the general population (5–8).
Until now, nasopharyngeal Real-Time Polymerase Chain Reaction (RT-PCR) is the gold standard diagnostic test for COVID-19 (5–8). RT-PCR has multiple limitations, including delayed availability of results and the need for specialized laboratory equipment as well as specialized technicians (1, 5, 6, 8). As a result, the number of tests performed per day is restricted by these limitations, risking delaying the appropriate management of positive cases. Therefore, other diagnostic techniques are needed to limit the virus’s spread and effectively monitor the degree of COVID-19 infection in the population (1, 5, 6, 8). Current literature explores the possibility of using point-of-care rapid antigen tests as a cost-effective and simple modality that has been used effectively with other viruses such as Influenza and respiratory syncytial virus (RSV) (9). However, the studies report an overall low sensitivity and high specificity compared to RT-PCR (1, 5, 6, 8).
Our study explores nasal swabs’ diagnostic performance as they do not require a skilled professional, are less time consuming, and cause less discomfort. Furthermore, nasal swabs—which are routinely used in microbiology labs with no risk of supply disruption—have been validated as an alternative procedure to collect nasal secretions, with nearly equivalent detection abilities to nasopharyngeal swabs (10). Nasopharyngeal swabs however are the reference sampling method for the detection of SARS-COV-2 as per the World Health Organization (11). We aim to demonstrate the efficacy of nasal antigen tests in mildly symptomatic cases. This would provide a simple, reliable test that might eliminate negative cases with a certain level of confidence. Implementation of such tests will reduce the workload on healthcare professionals and institutions, as these tests can be done at clinics or home and facilitate reopening and relaxing nationwide restrictions.
Objective
To determine the nasal swab antigen test’s accuracy in detecting SARS-COV-2 compared to nasopharyngeal RT-PCR in mildly symptomatic individuals.
Methods
Study Population
The study involved 4,183 mild symptomatic individuals. Definition of “mildly symptomatic” individuals followed Bahrain’s protocol (12). It included fever (<38°C), loss of taste or smell, flu-like symptoms, sore throat, gastrointestinal symptoms, myalgia, and fatigue. The study participants were referred to the national testing center’s symptomatic hall at the Bahrain International Exhibition and Convention Center.
Setting
All testing was conducted in the symptomatic hall in the National Testing Centre at the Exhibition Centre in Manama, Bahrain.
Study Design
We conducted a cross-sectional study to determine the diagnostic performance of the rapid antigen test compared to RT-PCR. Two swabs were taken from each individual, one nasal swab for the antigen test and one nasopharyngeal swab for the RT-PCR. For rapid antigen test, Abbott panbio COVID-19 antigen rapid test device (Abbott Rapid Diagnostic Jena GmbH, Jena, Germany) to detect SARS-CoV-2 nucleocapsid protein was used. The contained membrane strip is pre-coated with immobilized anti-SARS-CoV-2 antibody on the test line and mouse monoclonal anti-chicken IgY on the control line (13). The nasopharyngeal samples for RT-PCR were transferred to a viral transport media immediately after collection and transported to a COVID-19 laboratory for testing. The RT-PCR test was conducted using Thermo Fisher Scientific (Waltham, MA) TaqPath 1-Step RT-qPCR Master Mix, CG on the Applied Biosystems (Foster City, CA) 7500 Fast Dx RealTime PCR Instrument. The assay used followed the WHO protocol and targeted the E gene. If the E gene was detected, the sample was then confirmed by RdRP and N genes (14). The E gene Ct value was reported and used in this study. Ct values >40 were considered negative. Positive (virus-like particles of SARS-CoV-2 and RNase P) and negative (RNase-free Water) controls were included for quality control purposes.
Sample Collection
All samples were collected by a trained healthcare professional in the national testing center. The nasal samples were collected using the nasopharyngeal swab provided with the RADT kit from both nostrils. Based on the CDC guidelines, the patient’s head was tilted back by 70°. The swab was inserted approximately 2 cm into the nostril while gently rotating it, rolling it several times before removing it. The swab tip was placed in the buffer fluid inside the extraction tube, with 5-drops of extracted specimen dispensed onto the specimen well (S) on the device. Results were read after 15 min.
The nasopharyngeal samples used for RT-PCR were collected through both nostrils from the nasopharynx using a nasopharyngeal swab. The nasopharyngeal swab was inserted into the nostril parallel to the palate until resistance was encountered, or the depth was equivalent to the distance of the nose from the ear. The swab was rolled and rubbed gently, left in place for multiple seconds, then removed slowly while rotating it and placed into the transport tube (15).
Participants
• Inclusion criteria:
° Suspected COVID-19 cases with mild symptoms [defined by Bahrain’s protocol (12)] presenting to the testing center.
• Exclusion criteria:
° Suspected cases with severe symptoms
° Any asymptomatic suspected case
Data Handling and Statistical Analysis
Antigen test results and RT-PCR result with the corresponding Ct value were collected for all mildly symptomatic cases. The antigen’s diagnostic performance was assessed using sensitivity, specificity, positive predictive value, negative predictive value, and respective 95% Confidence interval. Agreement between nasopharyngeal RT-PCR and nasal antigen tests was assessed using kappa coefficient of agreement. The Ct value of identified and missed cases by antigen tests were summarized using median and interquartile range. Ct Value of identified and missed cases were compared using a two sample t-test. All p-values were two-sided, and P < 0.05 was considered significant. Data collection was performed through a live google sheet and extracted to Microsoft Excel 2016. Statistical analysis was performed using STATA (16).
Ethical Considerations
Ethical and research approval was obtained from the National COVID-19 Research and Ethics Committee (approval code: CRT-COVID-2020-088). All methods and analysis of data were approved by the National COVID-19 Research and Ethics Committee and carried out according to the local guideline and ethical guidelines of the Declaration of Helsinki 1975. Written Informed consent was waived by the Research and Ethical Committee for this study due to the absence of any patient identifying information.
Results
A total of 4,183 mild symptomatic cases were tested by RT-PCR (using a nasopharyngeal sample) and by antigen test (using a nasal sample). 56.5% of the cases were males, and 43.5% were females. The mean age of the tested population was 30.9 years (± 14.5 years). Days from symptom onset ranged from 0 to 14 with a median of 2 (IQR 1–3). Table 1 summarizes the demographics of the tested cohort. 17.5% (733/4,183) of the population tested positive by RT-PCR; no equivocal results were reported. Using the antigen test, 15.1% were positive, while the remaining tested negative, and none of the tests were equivocal.
