Coronavirus disease-2019 (COVID-19) is an infectious disease caused by a newly discovered coronavirus called Severe Acute Respiratory Coronavirus 2 (SARS-CoV2) [1]. The SARS-CoV2 belongs to a family of viruses that cause illness with various symptoms such as pneumonia, fever, breathing difficulty and lung infections [2].

The Coronavirus disease 2019 (COVID-19) pandemic has spread worldwide since its first recorded case in December 2019 [3]. Since the report of the index case in Nigeria in February 2020 by the Nigeria Center for Disease Control (NCDC), daily records of confirmed cases have been reported in several states in the country, including Ondo State. As of 28th August 2020, a total of 53,477 cases and 1011 deaths have been reported in Nigeria, while Ondo state ranked 11th among the states with a high number of confirmed cases in the country [4].

The Federal Ministry of Health through the Nigeria Centre for Disease Control (NCDC) has prioritized testing as one of the key strategies for the COVID-19 response in Nigeria. To contain the outbreak, the Government of Nigeria plans to rapidly scale-up diagnostic testing to cover all states and cities in Nigeria (NCDC scaling up laboratory testing) [5].

As the Coronavirus disease 2019 (COVID-19) pandemic continues to spread across the states and cities in Nigeria, there is an urgent need for rapid, simple, and accurate tests to diagnose severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2) infection [3] [6]. In September 2020, the World Health Organization (WHO) announced the emergency use authorization of two Antigen (Ag)-based rapid diagnostic tests (RDTs) kits namely SD Biosensor and Abbott for COVID-19 testing based on available data on both RDTs showing their ability to correctly identify individuals with the disease (sensitivity > 80%) and to accurately identify those who do not have the disease (specificity > 97%) [5] [7].

Rapid identification of infected subjects is a cornerstone for controlling a pandemic like the COVID-19 pandemic [8] [9]. Easy-to-handle antigen tests can easily be performed and provide timely results, which is of particular importance in primary care and outside the laboratory settings. [6]. However, concerns exist regarding the sensitivity of these rapid diagnostic testing kits. Hence, the study evaluated the performance of the SARS-CoV-2 Ag-RDT compared with the real-time PCR for SARS-CoV-2 for COVID-19 screening at an orientation camp in a southwest state of Nigeria.

Our study recorded more males as respondents than females. This is consistent with the study in a similar setting by Arinze [20] titled “entrepreneurship education on entrepreneurial intention of fresh graduates: A study of NYSC orientation camp, Umunya” who reported 67.9% of respondents were males. This finding is also in consonance with the study of Odega and Mofolorunsho [15] where more males were reported than females in their study in the NYSC orientation camp in Delta state southern Nigeria. Although this phenomenon cannot be readily explained, as it is dependent on the unbiased deployment process by the federal government system of graduates from higher learning institutions for mandatory one-year national service exercise.

Also, most of the respondents in this study were below 30 years of age. This is consistent with the federal government of Nigeria’s NYSC deployment policy where graduates who graduated at less than 30 years of age from polytechnics or universities either in Nigeria or outside Nigeria are deployed for the NYSC scheme [15] [21]. Furthermore, most of the respondents in this study were corps members than the NYSC camp officials. This can be attributed to the fact that the deployed NYSC members were more than the NYSC camp officials during NYSC orientation camp exercises [15].

The sensitivity and specificity of the Standard Q COVID-19 Ag test for rapid detection of SARS-CoV-2 antigen in our study revealed a moderate sensitivity (78.16%) and good Specificity (100%). Previous studies have documented and reported a much higher sensitivity and specificity for COVID-19 Ag RDT. For Panbio, other studies have reported sensitivity ranging from 73.3% - 91.7% with specificity in the range of 94.9% - 100% [22] [23] [24] [25]. Notably, the highest reported sensitivity of 91.7%/98.9% was reported by Alemany et al. [22]. Chaimayo et al. [3] in a similar study in Thailand using Standard^TM Q COVID-19 Ag kit (SD Biosensor^®, Republic of Korea) showed a higher sensitivity of 98.33% and a specificity of 98.73%.

Similarly, the manufacturer of Standard^TM Q COVID-19 Ag kit (SD Biosensor^®, Republic of Korea) has reported a sensitivity and specificity of 84.38% (95% CI, 67.21% - 94.72%) and 100.00% (95% CI, 97.85% - 100%), respectively (total n = 202; positive n = 32; negative n = 170). The manufacturer evaluated the sensitivity of the kit at a trial site in Malaysia using 32 RT-PCR-positive nasopharyngeal swabs from symptomatic patients. The specificity of this test was evaluated by the R&D team of SD Biosensor using 170 RT-PCR-negative samples. The monoclonal antibody specific to SARS-CoV-2 N antigen coated on the Standard Q COVID-19 Ag test was produced from the WUHAN-01 strain, which is genetically closely related to the SARS-CoV-2 strains detected in Thailand [3] [26] [27].

However, some studies where SD Biosensor COVID-19 Ag RDT was validated have reported lower sensitivity than our study. Treggiari et al. [28] in their study titled “SARS-CoV-2 rapid antigen test in comparison to RT-PCR targeting different genes: a real-life evaluation among unselected patients in a regional hospital of Italy” reported a sensitivity of 66.82% and specificity of 99.89%.

The lower sensitivity recorded in our study compared to previous studies such as Chaimayo et al. [3] might be attributed to the use of a mixed population of symptomatic and asymptomatic persons as study participants, with the asymptomatic participants representing more than three-quarters of the study participants in our study. This is consistent with the previous studies reporting an overall sensitivity within the range of 60% - 70% in heterogeneous patients [28] [29] [30]. This could also be due to other factors such as the sample quality, sample handling and processing techniques.

Also, the sensitivity increased significantly with the time of testing in our study. Other possible explanations could be linked to different testing time, as the test could have been performed either at the early or late phase of infection. Because infection of SARS-CoV-2 occurs in a large proportion of the population with the asymptomatic presentation, precautions should be observed when interpreting the results of the Ag-RDT test in these subjects. Conversely, we found a high specificity (100%), demonstrating a low occurrence of false-positive outcomes of the antigen test. Similar specificity was also reported by other authors [28] [31]. Diagnostic accuracy measures of a test are strictly dependent on the prevalence of the disease. For our study, the calculated NPV was 94.59% and PPV was 100% respectively. This could be due to the fact the study was conducted during the second wave of the COVID-19 outbreak in Nigeria within which a high number of confirmed COVID-19 cases and deaths were recorded daily in the country. However, there is a need to interpret Ag-RDT results with caution especially in low prevalence settings, due to the possibility of false-positive result outcomes.

Also, our study showed that age and sex were significantly associated with the antigen test performance, a finding that requires further investigation.

A preliminary search revealed this is the first field evaluation of antigen RDTs for the COVID-19 screening test in Nigeria Also, the selection of participants was random irrespective of their health status whether they were symptomatic or asymptomatic resulting in understanding the performance of the rapid test kit among these different groups and generalization of the findings.

The limitation of our study includes two swabs taken from each subject, with one from each nostril. One was tested immediately with the antigen RDT and the other was placed in a transport medium for subsequent RT-PCR testing at a national reference laboratory. Thus, the two swabs could be regarded as two different samples from the same participant.

Also, the storage and transportation of the samples to the reference laboratory could have influenced the outcome of the results as on some occasions the samples were batched for at most a day or two before being transported to the laboratory.

Furthermore, the collection of swab samples was done by different scientists with varying background training which may have introduced variability into the content or yield of swab material, however, minimal training on sample collection was provided to the research team prior to implementation of the study.

However, the findings from the study will boost the confidence of healthcare practitioners in implementing the use of antigen RDTs for the COVID-19 screening test in Nigeria.

Our study shows evidence that Standard^TM Q COVID-19 Ag kit (SD Biosensor^®, Republic of Korea) showed comparable sensitivity and specificity with real-time RT-PCR assay and can be an appropriate rapid antigen test that could be used to screen for positive tests and reduce the laboratory turnaround time for the tests conducted to guide rapid decision-making for clinical management of persons infected with COVID-19 for especially in closed settings and other clinical care settings.

The authors wish to appreciate all who participated in this study, public health administrators and officials of the State Ministry of Health for their candid support during data collection and the research process and the laboratory officers who carried out the testing both on the field and the molecular laboratory.

Elvis Efe Isere and Matthew Temitope Oluwole conceived the study. Elvis Efe Isere, Matthew Temitope Oluwole and Moses Adewale Adejugbagbe conceived the statistical analysis plan. Elvis Efe Isere, Matthew Temitope Oluwole, Moses Adewale Adejugbagbe, Temitope Olajumoke Omoju, Oluwatosin Oni, Ikeoluwapo Ajayi, Nosa Eniye Omorogbe, Stephen Fagbemi and Tolulope Aderonke Fagbemi contributed to the statistical analysis, interpretation of the results and writing of the first draft of the manuscript. All authors reviewed and approved the final manuscript for publication.

Data are available on reasonable request.

The study was conducted as part of an outbreak investigation and control hence ethical approval was obtained from the Ondo state Health Research Ethics Committee with protocol number OSHREC14/12/21/409. Also, Informed consent was obtained from the respondents. They were made to understand that participation is voluntary and there was no consequence for non-participation. All information obtained was kept confidential.

The authors declare that no conflicts of interest exist in this work.

Isere, E.E., Oluwole, M.T., Adejugbagbe, M.A., Omoju, T.O., Oni, O., Ajayi, I., Omorogbe, N.E., Fagbemi, T.A. and Fagbemi, S. (2022) SARS-COV-2 Rapid Antigen Test in Comparison with RT-PCR for Laboratory Diagnosis of COVID-19 in a Southwest State of Nigeria. Open Journal of Epidemiology, 12, 387-400. https://doi.org/10.4236/ojepi.2022.124032