Head-to-head comparison of nasal and nasopharyngeal sampling using SARS-CoV-2 rapid antigen testing in Lesotho

Abstract

Objectives To assess the real-world diagnostic performance of nasal and nasopharyngeal swabs for SD Biosensor STANDARD Q COVID-19 Antigen Rapid Diagnostic Test (Ag-RDT). Methods Individuals ≥5 years with COVID-19 compatible symptoms or history of exposure to SARS-CoV-2 presenting at hospitals in Lesotho received two nasopharyngeal and one nasal swab. Ag-RDT from nasal and nasopharyngeal swabs were performed as point-of-care on site, the second nasopharyngeal swab used for polymerase chain reaction (PCR) as the reference standard. Results Out of 2198 participants enrolled, 2131 had a valid PCR result (61% female, median age 41 years, 8% children), 84.5% were symptomatic. Overall PCR positivity rate was 5.8%. The sensitivity for nasopharyngeal, nasal, and combined nasal and nasopharyngeal Ag-RDT result was 70.2% (95%CI: 61.3-78.0), 67.3% (57.3-76.3) and 74.4% (65.5-82.0), respectively. The respective specificity was 97.9% (97.1-98.4), 97.9% (97.2-98.5) and 97.5% (96.7-98.2). For both sampling modalities, sensitivity was higher in participants with symptom duration ≤ 3days versus ≤ 7days. Agreement between nasal and nasopharyngeal Ag-RDT was 99.4%. Conclusions The STANDARD Q Ag-RDT showed high specificity. Sensitivity was, however, below the WHO recommended minimum requirement of ≥ 80%. The high agreement between nasal and nasopharyngeal sampling suggests that for Ag-RDT nasal sampling is a good alternative to nasopharyngeal sampling.

Head-to head comparison of anterior nares and nasopharyngeal swabs for SARS-CoV-2 antigen detection in a community drive-through test centre in the UK

“…Results presented here demonstrate that AN swabs are equivalent to NP swabs for SARS-CoV-2 Ag-RDT testing giving comparable sensitivities, 50% LoD and 95% LoD for both Ag-RDTs brands evaluated here. Our results supports previous findings where AN and NP swabs were compared for the Ag-RDT Standard-Q (SD Biosensor, Inc., Korea) in Lesotho [6], but we reported a higher sensitivity compared to the 67.3% and 70.2% for AN and NP swabs previously described [6]. Studies on RT-qPCR have found lower sensitivity using AN swabs compared to NP swabs consistently [5].…”

“…The order of sample collection could have negatively biased the results obtained for AN swabs caused by a possible sample depletion. However, in the two studies that compared Ag-RDT using AN swabs, the AN swab was collected first and our reported sensitivity and specificity for AN swabs are greater than the previous studies [6,7]. Further, studies on RT-qPCR found lower sensitivity using AN swabs compared to NP swabs [5], even when AN swabs were collected first [15,18,19].…”

“…For Ag-RDTs, studies on Ag-RDTs comparing sensitivity on AN swabs and NP swabs are very limited, with only two reported studies performed on the same Ag-RDT brand, Standard-Q (SD Biosensor, Inc., Korea), one study on professional taken swabs [6] and another in self-taken [7]. Sensitivity obtained with AN swabs was comparable (although 3% to 5% lower) than with NP swabs sensitivity but neither of the swab types fulfilled WHO target product profile (TPP) standards in any of the two studies [8].…”

Impact of a multi-disease integrated screening and diagnostic model for COVID-19, TB, and HIV in Lesotho

“…In the case of COVID-19 cases, a PCR test was used as the gold standard for diagnosis during most part of 2021. Later on, diagnosis was based on the result of the SARS-CoV-2 STANDARD Q COVID-19 Ag test, that has shown relatively low diagnostic performance in our setting (42). Anecdotically, a number of the 2252 (34%) eligible adults and children that presented with symptoms but did not enroll in this service model despite being eligible, were still tested for COVID-19 by the study staff, especially in periods were hospital health staff in other departments was scarce, however, these individuals are not included in this analysis.…”

“…On the other hand, the overall TB and HIV linkage to care rates within four weeks of diagnosis were higher than reported in similar experiences (45)(46)(47)(48), however when comparing to global targets, this model fell short in ART initiation rates (75% vs 95%), and met the TB treatment initiation target (90% vs. 90%) (49,50). As the COVID-19 pandemic surged, and lockdowns led to the cancellation of essential health services, global health actors advocated to adapt services that integrated TB, HIV and COVID-19 activities in sub-Saharan Africa (29,(42)(43)(44). This established an emerging body of evidence that evaluates the experiences and successes in the integration of services.…”