Introduction
Infection with Coronavirus (CoV) diseases (COVID-19), which is caused by novel sever acute respiratory syndrome CoV-2 (SARS-CoV-2), was firstly reported in Wuhan, China in December 2019 (Akashi et al., 2019). On 11 March 2020, the World Health Organization (WHO) declared COVID-19 as a pandemic of global concern (WHO, 11 March 2020.). After one year from the initial China outbreak, there have been tremendous increase in the number of confirmed cases as well as death records worldwide. As of 21 January 2021, ~ 95 million COVID-19 cases were confirmed worldwide and more than two million deaths were reported (WHO, 11 January 2020.). Egypt was among the first 10 countries in Africa that experienced COVID-19 cases (Nkengasong & Mankoula, 2020). By 3 January 2021, Egypt has reported 144.583 confirmed cases with 5.4% of them (7.918) died of the pandemic (WHO, 11 January 2020.). The sudden and unprecedented surge in the number of reported cases is overwhelming the capacity of the national healthcare system, particularly in the developing countries (Leung et al., 2020). Central to the containment of the ongoing pandemic is the availability of rapid and accurate diagnostic tests that could pinpoint patients at early disease stages before further spread occur.
Reverse transcriptase quantitative real-time PCR (RT-qPCR) assay has been the gold standard for diagnosing COVID-19 in many health sectors and laboratories (Shen et al., 2020; Tang, Schmitz, Persing, & Stratton, 2020; van Kasteren et al., 2020). However, this assay often done in large centralized hospitals or laboratories away from the access of local inhabitants, it requires long time-to-results, skilled staff and specialized instruments and is of high cost. This is particularly the case in many developing countries, including Egypt (Anjum, Anam, & Rahman, 2020). In Egypt, the RT-qPCR diagnosis is mostly done in Cairo, the capital or in capitals of governorates leading to an overall turn-around-time of ~ 24 hours at best between shipping the samples and obtaining the results (Sheridan, 2020). Indeed, suspected individuals often go first to the local clinics for emergency where RT-qPCR might not be available. The RT-qPCR may not be able to cope with the testing or screening needs in the low and middle-income countries due to limited infrastructure, low fund and limited human resources (Olalekan et al., 2020). To fill in this gap and to improve this situation, rapid antigen tests (RATs) are being developed and are in use as point-of-care diagnostic tools in local settings and emergency departments (Wee et al., 2020). They offer the advantage of being quick and can be done simply without need for special equipment (Lambert-Niclot et al., 2020; Nalumansi et al., 2020; Scohy et al., 2020). Determining the diagnostic performance of commercialized RAT is crucial because this gives indication about their reliability and clinical utility during the time of pandemic.
There have been many RAT available for diagnosis of COVID-19 (reviewed in (Olalekan et al., 2020)), yet their clinical applicability is questionable because their accuracy is low as compared to RT-qPCR, their diagnostic performance is highly variable, even when the same assay was applied in two different population with different ethnicity background (Chaimayo et al., 2020; Nalumansi et al., 2020) and their accuracy is host- and virus-dependent (Chaimayo et al., 2020; Tang et al., 2020). Similar to other countries, several RATs have been under development in Egypt, but the available studies lack detailed characterization of RAT performance, especially the impact of patients criteria, clinical features, sampling time and viral load on the test performance. Actually, only one RAT (BIOCREDIT COVID-19 antigen test) has been recently evaluated in Egypt (A. M. Abdelrazik, S. M. Elshafie, & H. M. Abdelaziz, 2020). In the current study, we aimed to add to the current knowledge by evaluating the clinical utility of a recently commercialized RAT, Standard ™ Q COVID-19 Ag, in a number of Egyptian participants, who are suspected of having COVID-19. We also studied the influence of various factors on the assay performance and tested the hypothesis that measuring laboratory parameters could enhance RAT predictive accuracy when RT-qPCR is not available.