- • Most of patients with mild symptoms (up to 75%) and close contacts are visited and followed-up in primary health care centers or test sites.
- • The present study is the largest evaluation of the Panbio Ag-RDT in samples from symptomatic and asymptomatic patients in real-world context.
- • We found an overall sensitivity of the Panbio™ rapid antigen test of 71.4% (95% CI: 63.1%, 78.7% and a specificity of 99.8% (95% CI: 99.4%, 99.9%)
- • Our results support the use of the Ag-RDT for symptomatic patients within 5 days since the onset of the symptoms in PHC setting and test sites.
We aimed to evaluate the accuracy of the Panbio™ Ag-RDT at primary health care (PHC) centers and test sites in symptomatic patients and close contacts, using the Reverse-Transcription Polymerase Chain Reaction (RT-PCR) test as the gold standard.
The study was conducted in four PHC centers and two test sites in Mallorca, Spain. Consecutive patients older than 18 years, attending the sites for RT-PCR testing were included. Two nasopharyngeal samples were collected, one for RT-PCR and the other was processed on-site using the Panbio™ rapid antigen test kit for SARS-CoV-2. The sensitivity and specificity were calculated using RT-PCR as the reference, and the predictive values using the pretest probability results for each analyzed group.
A total of 1369 participants were included; mean age 42.5 ± 14.9 years and 54.3% women. The overall prevalence was 10.2%. Most participants (70.6%) presented within 5 days of the onset of symptoms. The overall sensitivity was of 71.4% (95% CI: 63.1%, 78.7%), the specificity of 99.8% (95% CI: 99.4%, 99.9%), the positive predictive value of 98.0% (95% CI: 93.0%, 99.7%) and a negative predictive value of 96.8% (95% CI: 95.7%, 97.7%). The sensitivity was higher in symptomatic patients, in those arriving within 5 days since symptom onset and in those with high viral load.
Ag-RDT had relatively good performance characteristics in suspected symptomatic patients within five days since the onset of symptoms. However, our data do not support the sole use of Panbio™ Ag-RDT in asymptomatic individuals.
The COVID-19 pandemic is a significant challenge to the populations and health-care systems of countries throughout the world. The early detection of infected persons using massive and accurate testing, contact tracing, and rapid isolation are effective in slowing virus transmission. A Reverse-Transcription Polymerase Chain Reaction (RT-PCR) is currently the gold standard for diagnosis, but it has certain inconveniences, such as limited access to disposables and reagents in some regions, high cost, long processing time, and a need for specialized laboratories and trained personnel.
Rapid antigen detection tests (Ag-RDTs) were available soon after the COVID-19 pandemic began. These simple and inexpensive tests use lateral flow assays to detect proteins from the SARS-CoV-2 active infection. Nevertheless, research conducted early during the COVID-19 pandemic reported they had unsatisfactory diagnostic performance1, especially a low sensitivity2. A Cochrane systematic review of 8 studies of 5 different antigen tests reported an average sensitivity of 56.2% (95% confidence interval [CI]: 29.5%, 79.8%) and a mean specificity of 99.5% (95% CI: 98.1%, 99.9%)3.
More recent studies have reported improved accuracy of Ag-RDTs, especially for patients with high viral loads, i.e. patients who present within 5 days since symptom onset2. On 11 September, the World Health Organization (WHO) published an interim guidance that recommended use of an Ag-RDT for diagnosis of COVID-19 when the RT-PCR test is not available. The WHO recommended that an Ag-RDT test must have a sensitivity of at least 80% and a sensitivity of at least 97%, based on the gold-standard RT-PCR test4. A patient with a positive Ag-RDT result within 5 days of symptom onset can be considered to have a SARS-CoV-2 infection because these individuals are more likely to have high viral loads. However, a negative result should be interpreted with caution, especially in patients with high pretest probability and confirmatory RT-PCR test following a negative Ag-RDT test is recommended5.
Ag-RDTs are promising point-of-care alternatives because they can be produced at low cost in high volume, are easy to use, and provide results within 15 min, thus allowing quicker clinical decisions. However, the RT-PCR test remains the gold standard for diagnosis because prospective and real-world data on the performance of Ag-RDTs are currently limited4. Nevertheless, for low- and middle-income countries that lack the resources to implement national RT-PCR testing strategies, the WHO has announced the availability of 120 million Ag-RDT kits6. Moreover, the Bill & Melinda Gates Foundation executed separate volume guarantee agreements with Abbott and SD Biosensor for production of an Ag-RDT.
Europe is currently experiencing a second wave of the COVID-19 pandemic and there is a greater demand for diagnostic testing. Fast diagnostic testing using an inexpensive, point-of-care, easy-to-use, and rapid technique might help alleviate the burdens experienced by testing laboratories and caregivers in primary healthcare (PHC) centers and COVID-19 test sites7. The increased demand for RT-PCR tests can cause delays in reporting of positive results and lead to delays in contact tracing, and thus have negative consequences for control of the COVID-19 pandemic.
Most previous studies that evaluated Ag-RDTs for COVID-19 examined symptomatic patients, were conducted in the setting of hospital emergency services, and examined patients who presented with moderate or severe symptoms of COVID-19. Thus, rigorous studies are needed before Ag-RDTs can be used for the diagnosis of SARS-CoV-2 in the setting of PHC centers or in the community.
The Panbio™ rapid antigen test kit for SARS-CoV-2 (Abbott Diagnostic GmbH, Jena, Germany) is a qualitative test using specimens from nasopharyngeal swabs. The manufacturer reported that the sensitivity for symptomatic patients was 93.3% overall and 98.2% in those RT-PCR cycle threshold (Ct) ≤33, and that the specificity was 99.4%8.
The main aim of this study was to evaluate the performance of the Panbio Ag-RDT at PHC centers and test sites in symptomatic patients and close contacts, using the RT-PCR test as the gold standard.
Design and setting
This prospective diagnostic study was conducted in Mallorca (Balearic Islands, Spain) from October 2–25, 2020. Two testing locations (COVID-EXPRESS) that cover the city of Palma and 4 PHC centers (Santa Ponça, Alcudia, Inca, and Coll d’en Rebassa) were included.
Individuals were invited to participate if they were older than 18 years, were not previously diagnosed with COVID-19, attended one of the above-named settings for RT-PCR testing, had symptoms suggestive of infection with referral by a general practitioner (GP), or had a close contact with another patient with an RT-PCR-confirmed infection.