RR:C19 Evidence Scale rating by reviewer:
Reliable. The main study claims are generally justified by its methods and data. The results and conclusions are likely to be similar to the hypothetical ideal study. There are some minor caveats or limitations, but they would/do not change the major claims of the study. The study provides sufficient strength of evidence on its own that its main claims should be considered actionable, with some room for future revision.
The authors evaluated the performance of the Panbio Abbott COVID-19 Rapid Antigen Test (RAT) to detect COVID-19 cases. COVID-19 cases were defined by RT-PCR.
The study was well-planned. It showed that the sensitivity of RAT to detect COVID-19 cases was higher in symptomatic individuals than asymptomatic individuals. However, the manuscript can be improved further.
This review was divided into two parts. The first part was the review of the manuscript, the second part was the recommendations of the manuscript.
1. Review of the manuscript
1.1 Aims of the study
Existing method: RT-PCR was used to detect SARS-CoV-2 among symptomatic individuals. Asymptomatic individuals were also tested for contact cases and cases through contact tracing.
Suggested method: To assess if RAT can reduce the workloads on laboratories in Sint Maarten.
A statistics test was used to assess the minimum sample size needed. All ages of individuals irrespective of symptoms were recruited. The study period was from 11 Jan 2021 to 26 Feb 2021. One nasopharyngeal (NP) swab was for RAT while another NP swab was for RT-PCR. Three groups of data were collected and analyzed: (1) demographics, (2) clinical information, (3) test results.
Among the 1411 individuals tested having Ct values, the prevalence of COVID-19 cases were 8.4% and 9.6% when Ct values cut-off were <33 and <35 respectively. Variables of having COVID-19 were assessed thoroughly to see if they were statistically significant.
Regarding RAT performance, when Ct values cut-off was <33, the sensitivity of RAT were 84.0%, 90.5%, 67.7% for overall, symptomatic and asymptomatic individuals respectively. The specificity was high, ≥99.9 among the three groups of individuals.
The diagnostic accuracy of the RAT found in the study was compared and discussed with other studies using the same RAT kit.
Limitations of the study were recognized.
The proposed usage of RAT based on the findings of the study was recommended.
2. Recommendations of the manuscript
2.1 Aims of the study
The aims of the study were clearly defined.
The sample size calculation of this study was based on the 5% of prevalence of COVID-19. The authors are recommended to justify this estimation.
The following technical operations of this study should be elaborated:
The place where respiratory specimens collected
If RAT was performed on-site
Was NP swab kept in viral transport medium tube for RT-PCR?
The conditions of temporary storage of NP swabs
Was there same-day transportation of NP swabs to St Maarten Laboratory for RT-PCR
Were RT-PCRs performed daily without freeze and thaw
The exact amplification cycles (e.g. 40 or 45) of the SARS-CoV-2 RT-PCR assay
COVID-19 positive cases should be defined using the same criteria as the routine practice, Ct<35
COVID-19 positive cases in Tables 1-3 were based on different Ct cut-off values. Table 1 was defined as Ct<35 while Tables 2-3 were defined as Ct<33. COVID-19 positive cases should be presented and reported using the same criteria.
The authors were right to present the performance of RAT on different viral load samples (Table 4).
An additional table can be prepared to present the distributions of different viral load samples (i.e. Ct<35, <30, <25) for symptomatic individuals and asymptomatic individuals.
It is not necessary to adjust the Ct values to fit the guidelines or share concordant results with other studies. On the contrary, it is better to discuss the underlining reasons for finding discordant results.
The authors can also discuss the performance of RAT will be different when the prevalence of COVID-19 is changed. When prevalence increases, the sensitivity of RAT increases since the probability of having a positive case is increased. Conversely, when prevalence decreases, the specificity of RAT decreases since the probability of having a positive case is reduced . This issue of discussion should be concordant with the findings based on the new table recommended in section 2.3.
3. Conflicts of interest
1. WHO. SARS-CoV-2 antigen-detecting rapid diagnostic tests: An implementation guide, 21 December 2020. Available at: https://www.who.int/publications/i/item/9789240017740 (Accessed: 11 October 2021).