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Same-day SARS-CoV-2 antigen test screening in an indoor mass-gathering live music event: a randomised controlled trial

Our take —

This randomized controlled open-label trial assessed the difference in incidence of SARS-CoV-2 infection among 1,047 adults randomized to enter (experimental) or not enter (control) an indoor concert event in Spain. Nasopharyngeal swabs were tested using antigen-detecting rapid diagnostic tests (Ag-RDT), with follow-up reverse transcriptase polymerase chain reaction (RT-PCR) confirmation before the concert event and eight days after the event. Two control participants tested positive for SARS-CoV-2 during the follow-up visit, but this difference was not statistically significant. The results suggest mass indoor gatherings may be attended without increased risk of transmission, in a setting with low current transmission, if screening and other prevention measures are adopted, but additional studies are needed to confirm these findings and context related to vaccine coverage was missing.

Study design

Randomized Controlled Trial

Study population and setting

Using a randomized controlled open-label trial, authors assessed the incidence of RT-PCR-confirmed SARS-CoV-2 among 1,047 participants aged 18-59 years attending an indoor concert in Sala Apolo, Barcelona, Spain. Participants were tested for SARS-CoV-2 using the Panbio COVID-19 Rapid Test (an antigen-detecting rapid diagnostic test [Ag-RDT]) and a transcription-mediated amplification (TMA) test within 12 hours of the concert. Participants with a positive Ag-RDT result were excluded and positive TMA results were retested using RT-PCR. Among those with a negative Ag-RDT result, participants were block-randomized 1:1 to either enter the concert (experimental) or not enter the event and return home (control). Block randomization is a type of randomization that divides potential participants into n blocks of a predetermined size, and randomly allocates participants within blocks to the experimental or control group. Participants randomized to enter the event were required to wear an N95 mask for the duration of the event, except when in a socially distanced outdoor smoking area or when eating or drinking in defined locations. Eight days after the concert, all participants (those who entered and those who did not) were visited for a nasopharyngeal swab collection for Ag-RDT, TMA, and PCR testing. Authors also estimated the negative predictive value (NPV) of the Ag-RDT.

Summary of Main Findings

No participants tested positive for SARS-CoV-2 prior to the event via Ag-RDT; 465 participants entered the event and had a follow up visit and 495 participants who did not enter the event had a follow up visit, resulting in 960 total participants included in the analysis. Of those included, the mean age was 33.6 years and 82% were male. At baseline, 13 (3%) participants in the experimental group and 15 (3%) in the control group had a positive TMA test; of which one experimental and one control participant had a positive RT-PCR result with CT values = 37, indicating levels of viral detection. All individuals with a positive baseline TMA result had a documented prior case of infection in the recent past (median 50 days). Nine experimental and 11 control participants who were TMA-negative at baseline had a positive TMA test eight days after the concert; two of these controls (0.4% of total) were positive via Ag-RDT and RT-PCR. Incidence of SARS-CoV-2 infection did not differ significantly (-0.15% [-0.72 to 0.44]) between the two groups. The NPV of the Ag-RDT for a positive RT-PCR was 99.9% (99.5-100).

Study Strengths

Randomized trials are considered the gold standard for evaluating the effectiveness of an intervention and is the most rigorous study design for hypothesis testing. The study used three separate tests for SARS-CoV-2 infection and the use of RT-PCR likely eliminated the risk of false negative results among participants.

Limitations

Clinical trials are often limited by the modification of behavior by participants who know they are being observed; however, post-event questionnaire results suggest this was not a major concern in this study. The analytic sensitivity of Ag-RDTs is lower than RT-PCR and likely only reliable for ruling out virus transmission within a few hours following the test (i.e., cannot be used to rule out longer term transmission). Overall, despite apparent effectiveness of mass screening prior to the event, such measures may not be sustainable on a larger scale. Transmission of SARS-CoV-2 was low in the population from which study participants were drawn – study results may differ in populations with higher disease burden. Finally, due to the time of the study (mid-December 2020) and the availability of COVID-19 vaccines in Spain (late December 2020), the effect of vaccination – an important factor needed to properly contextualize results – can not be assessed.

Value added

This randomized controlled open-label trial demonstrated the effectiveness of mass screening for SARS-CoV-2 and mask wearing in a densely populated indoor concert space. It is the first randomized clinical trial to assess risk of SARS-CoV-2 transmission under these settings and using these preventative measures.

This review was posted on: 30 July 2021