Diagnostic accuracy of the Panbio COVID-19 antigen rapid test device for SARS-CoV-2 detection in Kenya, 2021: A field evaluation

Abstract

Background Accurate and timely diagnosis is essential in limiting the spread of SARS-CoV-2 infection. The reference standard, rRT-PCR, requires specialized laboratories, costly reagents, and a long turnaround time. Antigen RDTs provide a feasible alternative to rRT-PCR since they are quick, relatively inexpensive, and do not require a laboratory. The WHO requires that Ag RDTs have a sensitivity ≥80% and specificity ≥97%. Methods This evaluation was conducted at 11 health facilities in Kenya between March and July 2021. We enrolled persons of any age with respiratory symptoms and asymptomatic contacts of confirmed COVID-19 cases. We collected demographic and clinical information and two nasopharyngeal specimens from each participant for Ag RDT testing and rRT-PCR. We calculated the diagnostic performance of the Panbio™ Ag RDT against the US Centers for Disease Control and Prevention’s (CDC) rRT-PCR test. Results We evaluated the Ag RDT in 2,245 individuals where 551 (24.5%, 95% CI: 22.8–26.3%) tested positive by rRT-PCR. Overall sensitivity of the Ag RDT was 46.6% (95% CI: 42.4–50.9%), specificity 98.5% (95% CI: 97.8–99.0%), PPV 90.8% (95% CI: 86.8–93.9%) and NPV 85.0% (95% CI: 83.4–86.6%). Among symptomatic individuals, sensitivity was 60.6% (95% CI: 54.3–66.7%) and specificity was 98.1% (95% CI: 96.7–99.0%). Among asymptomatic individuals, sensitivity was 34.7% (95% CI 29.3–40.4%) and specificity was 98.7% (95% CI: 97.8–99.3%). In persons with onset of symptoms <5 days (594/876, 67.8%), sensitivity was 67.1% (95% CI: 59.2–74.3%), and 53.3% (95% CI: 40.0–66.3%) among those with onset of symptoms >7 days (157/876, 17.9%). The highest sensitivity was 87.0% (95% CI: 80.9–91.8%) in symptomatic individuals with cycle threshold (Ct) values ≤30. Conclusion The overall sensitivity and NPV of the Panbio™ Ag RDT were much lower than expected. The specificity of the Ag RDT was high and satisfactory; therefore, a positive result may not require confirmation by rRT-PCR. The kit may be useful as a rapid screening tool only for symptomatic patients in high-risk settings with limited access to rRT-PCR. A negative result should be interpreted based on clinical and epidemiological information and may require retesting by rRT-PCR.

Regional Evaluation of Two SARS-CoV-2 Antigen Rapid Diagnostic Tests in East Africa

“…Therefore, RDTs might give false-negative results during large-scale, cross-sectional screening of populations (such as truck-drivers, tourists, commuters). This finding is consistent with other recently published studies in Africa ( 8 , 9 ), and are especially relevant to mobile laboratory settings such as the EAC Mobile laboratory in Nimule/South Sudan screening transient populations, which was reflected in a high percentage of recent travel history and low percentage of symptomatic cases. As a matter of fact, seven EAC Mobile Laboratories were deployed to respective border regions during the pandemic ( 11 ), screening over 1 million people with RT-PCR, with the majority being asymptomatic.…”

“…The overall sensitivity of the RDTs to detect low viral load patients was much lower than both that reported by the manufacturers and relative to the gold qRT-PCR standard. This may be attributed to a number of factors, including the possibility of skewed selection of higher viral load samples for manufacturer test validation ( 9 ). Therefore, RDTs might give false-negative results during large-scale, cross-sectional screening of populations (such as truck-drivers, tourists, commuters).…”

“…Many SARS-CoV-2 antigen RDTs have been evaluated globally ( 3 – 5 ), including through the framework of the Foundation of Innovative Diagnostics (FIND) ( 6 ), but there is very little performance information in East African populations, especially in a real world setting, i.e. in the hands of the laboratory personnel carrying out the testing of local populations at points-of-entry, community-level, or health facilities ( 7 – 9 ).…”

Laboratory Evaluation of a SARS-CoV-2 RT-LAMP Test

“…The observed diagnostic performance of the RT-LAMP test under evaluation (sensitivity 97.2%; specificity 100%) exceeded the WHO recommendations for Ag-RDTs, which should have a minimal sensitivity of 80% and a minimal specificity of 97% [ 6 ]. The RT-LAMP test also met the sample size assumptions of having a sensitivity and specificity of >97%.…”

“…However, the implementation of real-time RT-PCR requires specialized laboratories, infrastructure and personnel, and costly reagents and equipment, which are often not widely available in LMICs. Antigen detection based rapid diagnostic tests (Ag-RDTs) represent an attractive alternative, because of their low cost and ease of operation, but concerns about their sensitivity limit their use at particularly low viral loads [ 3 , 4 , 5 , 6 , 7 , 8 , 9 ].…”