The initial community clinical study and the evaluation post-implementation by POCT at community assessment centres demonstrated similar sensitivity. Overall, the sensitivity of the Panbio was moderate at 86.1–87.7% compared to various RT-PCR platforms for this population. This study demonstrates that acceptable sensitivity is achieved for clinical use with the Panbio, but confirmatory testing of negatives is likely necessary for most populations.
Use of rapid antigen tests, such as the Panbio, for the detection of SARS-CoV-2 among symptomatic individuals within the community remains a worthwhile endeavour. Although confirmatory testing of negatives is recommended, identifying positives at the point of care has several advantages. It can speed important public health measures, such as contact tracing and isolation. Moreover, it has significant benefits for the laboratory in terms of decreasing error and improving laboratory processes. For instance, decreasing the number of positive samples entering the laboratory can decrease the risk of false positive results by reducing the probability of SARS-CoV-2 contamination during RT-PCR testing. In addition, the decrease in positive samples can improve efficiencies in other laboratory processes, such as pooling.
While there were two instances in our initial clinical evaluation of known COVID-19 individuals where the Panbio was positive and the RT-PCR was negative, we believe these are true positives based on several reasons. Participants recruited in our study were all recently diagnosed with COVID-19; none of the samples from the asymptomatic individuals at low risk of COVID-19 gave false positive results throughout the study; and no issues with false positive results have been identified by the Panbio manufacturer or among previous Panbio publications within the literature.2–5 Most likely, the two false negative results from RT-PCR was related to differences in sample collection among individuals with low SARS-CoV-2 virus load present.
The sensitivity of the Panbio varies in the literature from 72.6–86.5% among individuals with symptoms ≤ 7 days.2–5 These studies varied in terms of their study design and reference standards used. All studies examined paired NP swabs tested with the Panbio and a PCR-based platform, with two of the four studies using the Allplex (Seegene, South Korea).3,4 One study2 used the VitaPCR SARS-CoV-2 (Credo diagnostics, Singapore) that has limited data available on its performance, which may potentially explain why 7 samples were Panbio positive but VitaPCR SARS-CoV-2 negative.10 Gremmels et al. performed testing on the Panbio up to 2 hours from collection, which may account for the lower sensitivity detected (72.6%).3 Of the studies that examined positivity rate based on symptom duration, one study found no difference in positivity rate with duration of symptom onset3, another found higher sensitivity in individuals with symptom onset < 7 days (sensitivity 86.5%) compared to individuals with symptom onset ≥ 7 days (sensitivity 53.8%)4, and another found slightly higher sensitivity in individuals with symptoms < 5 days (sensitivity 80.4%) compared to individuals with symptoms ≤ 7 days (79.6%).5 We found no difference in Panbio sensitivity among individuals with symptoms > 7 days, but this was limited to a very small pool of samples (N = 15). All studies, including ours, found decreases in Panbio sensitivity among SARS-CoV-2 samples with higher Ct values, with sensitivity dropping when Ct values are approximately > 26.
Our study contributes to the literature on the Panbio’s performance by using alternative collection methods, such as throat and saliva swabs. Unfortunately, these specimens were proven to be inferior to NP swabs and should not be used on the Panbio. Further studies are required to determine if an alternative way to test saliva on the Panbio could prove effective (e.g. direct inoculation of saliva onto the Panbio test cartridge or saliva collected in a media). We did not evaluate nasal swabs on the Panbio because the results could have been affected by the concurrent collection of paired NP swabs. However, previous work done by our laboratory has shown nasal swabs to be inferior to throat swabs for the detection of SARS-CoV-2, so it would be surprising if nasal swabs proved to be as effective a specimen as NP swabs for testing on the Panbio.7
Our study was predominately restricted to individuals within the community who had symptoms ≤ 7 days. As such, our study was unable to provide any conclusions about the Panbio performance among individuals admitted to hospital, in congregate living facilities, who are asymptomatic, and individuals with symptoms > 7 days. The strengths of our study include the large number of COVID-19 positive individuals recruited. In addition, we included prospective data taken from clinical settings (symptomatic individuals presenting to COVID assessment centres) and found similar results, which further reinforces our study findings. We also tested asymptomatic individuals at low risk of COVID-19 (no travel, no exposure), and tested retrospective samples positive for other respiratory viruses.