key: cord-0269826-ql05sozc
authors: Konstantinus, I. S.; Chiwara, D.; Ndevaetela, E.-E.; Ndarukwa-Phiri, V.; Garus-oas, N.; Frans, N.; Ndumbu, P.; Shiningavamwe, A.; van Rooyen, G.; Schiceya, F.; Hlahla, L.; Namundjebo, P.; Ndozi-Okia, I.; Chikuse, F.; Hailu Bantiewalu, S.; Tjombonde, K.
title: Laboratory and field evaluation of the STANDARD Q and PanbioTM SARS-CoV-2 antigen rapid test in Namibia using nasopharyngeal samples
date: 2021-09-23
journal: nan
DOI: 10.1101/2021.09.21.21263886
sha: 7bc9a7ce4ecc115bfe97f549e619a769ccefa89c
doc_id: 269826
cord_uid: ql05sozc

Abstract Background As new SARS-CoV-2 variants of concern emerge, there is a need to scale up testing to minimize transmission of the Coronavirus disease 2019 (COVID-19). Many countries especially those in the developing world continue to struggle with scaling up reverse transcriptase polymerase reaction (RT-PCR) to detect SARS-CoV-2 due to scarcity of resources. Alternatives such as antigen rapid diagnostics tests (Ag-RDTs) may provide a solution to enable countries to scale up testing. Methods In this study, we evaluated the PanbioTM and STANDARD Q Ag-RDTs in the laboratory using 80 COVID-19 RT-PCR confirmed and 80 negative nasopharyngeal swabs. The STANDARD-Q was further evaluated in the field on 112 symptomatic and 61 asymptomatic participants. Results For the laboratory evaluation, both tests had a sensitivity above 80% (PanbioTM = 86% vs STANDARD Q = 88%). The specificity of the PanbioTM was 100%, while that of the STANDARD Q was 99%. When evaluated in the field, the STANDARD Q maintained a high specificity of 99%, however the sensitivity was reduced to 56%. Conclusion Using Ag-RDTs in low resource settings will be helpful, however, negative results should be confirmed by RT-PCR where possible to rule out COVID-19 infection.

As new SARS-CoV-2 variants of concern emerge, there is a need to scale up testing to minimize transmission of the Coronavirus disease 2019 . Many countries especially those in the developing world continue to struggle with scaling up reverse transcriptase polymerase reaction (RT-PCR) to detect SARS-CoV-2 due to scarcity of resources. Alternatives such as antigen rapid diagnostics tests (Ag-RDTs) may provide a solution to enable countries to scale up testing.

In this study, we evaluated the Panbio TM and STANDARD Q Ag-RDTs in the laboratory using 80 COVID-19 RT-PCR confirmed and 80 negative nasopharyngeal swabs. The STANDARD-Q was further evaluated in the field on 112 symptomatic and 61 asymptomatic participants.

For the laboratory evaluation, both tests had a sensitivity above 80% (Panbio TM = 86% vs STANDARD Q = 88%). The specificity of the Panbio TM was 100%, while that of the STANDARD Q was 99%. When evaluated in the field, the STANDARD Q maintained a high specificity of 99%, however the sensitivity was reduced to 56%.

Using Ag-RDTs in low resource settings will be helpful, however, negative results should be confirmed by RT-PCR where possible to rule out COVID-19 infection.

The pandemic caused by Severe Acute Respiratory Syndrome Coronavirus 2 (SARS-CoV-2) identified originally in China has now become a public health throughout the world, and we are now dealing with emerging variants of concern (VOCs) of which some are more infectious compared to the founder virus [1, 2] . Reverse transcription polymerase chain reaction (RT-PCR) is the laboratory gold standard method to detect SARS-CoV-2 in people with coronavirus disease 2019 (COVID-19). However, this method has its challenges such as long turnaround time, high-cost and requires trained laboratory personnel.

Due to the challenges of using RT-PCR, antigen-rapid diagnostic tests (Ag-RDTs) are being considered in several countries for epidemiological surveillance and even diagnostic purposes in symptomatic individuals [3] . These tests are less expensive, produce results faster than molecular tests; yielding results in as little as 15 to 30 minutes, and they do not require specialized laboratory techniques [4, 5] . The WHO recommended that Ag-RDTs that meet at least 80% sensitivity and 97% specificity can be utilized in settings where RT-PCR is limited [6] . The Namibian Medical Regulatory Council (NMRC) has proposed a framework for these tests to undergo incountry laboratory and field verification before being recommend for use.

In the present study, the Panbio TM and STANDARD Q were evaluated in detecting SARS-CoV-2 antigens in frozen nasopharyngeal samples The STANDARD Q test was further evaluated in the field using fresh nasopharyngeal samples. is the author/funder, who has granted medRxiv a license to display the preprint in (which was not certified by peer review) preprint 

The laboratory evaluation was a cross-sectional, retrospective verification of the performance of the STANDARD Q (SD Biosensor, Republic of Korea) and Panbio TM is the author/funder, who has granted medRxiv a license to display the preprint in (which was not certified by peer review) preprint

The copyright holder for this this version posted September 23, 2021. Negative Predictive Values (NPV) were also calculated. Mann-Whitney U test was computed to compare the differences between two groups using Prism V9 (GraphPad Software).

To determine the specificity and sensitivity of both Ag-RDT, frozen VTM from nasopharyngeal swabs were used. The sensitivity for the STANDARD Q was 88% (95% CI: 79% to 93%) and the specificity was 99% (95% CI: 93% to 99%), while that of Panbio TM was 86% (95% CI: 76% to 91%) and 100% (95% CI: 95% to 100%) respectively ( Table 1 ). The PPV for the STANDARD Q and Panbio TM was 99% and 100% respectively, while the NPV was 89% and 87% respectively. is the author/funder, who has granted medRxiv a license to display the preprint in (which was not certified by peer review) preprint We then compared samples which were SARS-CoV-2 positive using RT-PCR grouped according to their Ag-RDT results (Figure 1) . STANDARD Q had 70 true positives and 10 false negatives; and Panbio TM had 68 true positives and 12 false negatives.

Interestingly for both Ag-RDTs, samples which had a negative result were those with a high CT value. For STANDARD Q, the median CT value for the negative samples was 33 compared to a median CT value of 24 in the positive samples. The median CT value for the negative samples using the Panbio TM was 32 compared to that of 24 in the positive samples.

Nasopharyngeal samples from 173 participants were included in the field evaluation.

The demographic and clinical characteristics are shown in Table 2 . The median age was 33 years, with an almost equal distribution of females (51%) and males (49%). Of these participants, 65% (n=112) reported having symptoms onset within 5-7 days, with having a cough being the most prevalent symptom (37%) followed by headache (28%); while vomiting was the least common symptom in this cohort. A total of 36 samples tested positive by RT-PCR representing 21% positivity, of which 29 samples were from symptomatic and 7 were from asymptomatic participants. is the author/funder, who has granted medRxiv a license to display the preprint in (which was not certified by peer review) preprint We also compared the CT values in participants who were SARS-CoV-2 PCR positive grouped according to their STANDARD Q test result (Figure 2A) is the author/funder, who has granted medRxiv a license to display the preprint in (which was not certified by peer review) preprint

The copyright holder for this this version posted September 23, 2021. ; https://doi.org/10.1101/2021.09.21.21263886 doi: medRxiv preprint

Molecular testing is inherently difficult to scale up as it requires laboratories with specialized equipment and reagents which are costly, and trained laboratory personnel [4, 7] . By the end of 2020, African countries have seen an increase in COVID-19 cases in the second wave of the pandemic compared to the first wave, as new variants of concern such as the Beta and Delta reported to be more infectious spread across the continent [8, 9] . Namibia has not been spared from this, being one of the worst affected African countries during the third wave. Timely and accurate COVID-19 testing is a critical component of surveillance, contact tracing, infection prevention and control and clinical management of COVID-19 cases. Hence, there is a need to scale up testing and Ag-RDTs might be useful for this in resource limited countries including Namibia.

In this study, we evaluated two Ag-RDTs, Panbio TM and STANDARD Q. The laboratory evaluation showed a high specificity for both tests, with the Panbio TM at 100% compared to the STANDARD Q at 98%. In contrast, the sensitivity of the STANDARD Q was slightly higher at 88% compared to that of the Panbio TM at 86%. For the field evaluation, only the STANDARD Q Ag-RDT was evaluated due to its availability at the time of conducting the study. Although the STANDARD Q maintained a high specificity of 99% in the field, the test had a reduced sensitivity of 56%. The decreased field sensitivity is expected because the laboratory evaluation used selected SARS-CoV-2 positive samples compared to testing participants in the field with unknown SARS-CoV-2 status and based on their self-reported symptoms. Hence, the performance of these tests also depends on the settings they are being used and the prevalence of the disease at the time of the study.

Several studies have reported Ag-RDTs to be more sensitive in samples with low CT values as a result of high viral load [10] [11] [12] [13] [14] . This was also observed in our evaluation for both Ag-RDTs. In the laboratory evaluation, the false negative samples were similar for both STANDARD Q and Panbio TM with the later having an additional two samples, and these samples had a CT value above 25. One study reported sensitivity of the Panbio TM and STANDARD Q to be a 100% for samples with a CT value below 20, decreasing at 41% and 52% respectively for those samples with a CT value between . CC-BY-NC-ND 4.0 International license It is made available under a perpetuity.

is the author/funder, who has granted medRxiv a license to display the preprint in (which was not certified by peer review) preprint

The copyright holder for this this version posted September 23, 2021. ; https://doi.org/10.1101/2021.09.21.21263886 doi: medRxiv preprint 25-30 [14] . Other studies also reported the sensitivity of these two Ag-RDTs to increase above 80% when the CT value is <25 [7, 12, 13, [15] [16] [17] [18] [19] .

One of the limitations for this study included the credibility of the symptom onset of the participants included in the field of evaluation. We could not determine with certainty whether the samples collected were from patients whose symptoms onset was within 5-7 days. This is important because these tests have been reported to be more reliable in detecting SARS-CoV-2 infection within the first 7 days after the onset of symptoms. Therefore, they can miss individuals who are in the very early stage of infection (presymptomatic stage) and those who are in the late stage with a decreased viral replication.

In conclusion, these results add to the body of evidence that Ag-RDTs are useful and may be utilized to scale up testing to reduce viral transmission in settings where RT-PCR is a challenge. is the author/funder, who has granted medRxiv a license to display the preprint in (which was not certified by peer review) preprint

The copyright holder for this this version posted September 23, 2021. ; https://doi.org/10.1101/2021.09.21.21263886 doi: medRxiv preprint . CC-BY-NC-ND 4.0 International license It is made available under a perpetuity.

is the author/funder, who has granted medRxiv a license to display the preprint in (which was not certified by peer review) preprint

The copyright holder for this this version posted September 23, 2021. ; https://doi.org/10.1101/2021.09.21.21263886 doi: medRxiv preprint 

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We would like to thank the NIP COVID-19 Laboratory team, Dr Suzanne Beard from CDC, the Laboratory pillar at the Ministry of Health and Social Services (MoHSS) specifically Mrs Mary Mataranyika, and the staff at the Robert Mugabe and Katutura Health Centre.

The authors declare no conflict of interest