Open access Original research Evaluating the controlled reopening of nightlife during the COVID-­19 pandemic: a matched cohort study in Sitges, Spain, in May 2021 (Reobrim Sitges) Oriol Cunillera Puértolas ‍ ‍,1,2 Sara Contreras-­Martos,1,2 Mercè Marzo-­Castillejo ‍ ‍,1,2 Darío López Gallegos,3 Mateo Acedo Anta,4,5 Jesús Almeda Ortega ‍ ‍,1,2 Joan Colom,6 Josep Basora,7 Betlem Salvador-­Gonzalez1 To cite: Cunillera Puértolas O, ABSTRACT Contreras-­Martos S, Objectives To assess the impact of relaxing the state of STRENGTHS AND LIMITATIONS OF THIS STUDY Marzo-­Castillejo M, et al. alarm restrictions on SARS-­CoV-­2 infections at 14 days ⇒ Reobrim Sitges was a matched cohort study with Evaluating the controlled convenience sampling and with a paired control among people attending reopened nightclub venues. reopening of nightlife during group. the COVID-­19 pandemic: Design Matched cohort study with a paired control group (1:5 ratio). ⇒ Participants underwent rapid antigen diagnostic a matched cohort study in Sitges, Spain, in May 2021 Setting Five small nightclubs with indoor areas and tests (Ag-­RDTs) on the afternoon of the same day (Reobrim Sitges). BMJ Open outdoor terraces, in a nightlife-­restricted area in Sitges, prior to accessing the event. 2022;12:e058595. doi:10.1136/ Spain, on 20 May 2021. Wearing masks was mandatory, ⇒ Evidence of infection by SARS-­CoV-­2 at 14 days was bmjopen-2021-058595 drinking was allowed and social distance was not required. obtained from the electronic health records. Participants Volunteers were selected through a ⇒ Follow-­up Ag-­RDTs 6 days after the intervention ► Prepublication history for convenience sampling. To attend the event, participants minimised unregistered infections in the partici- this paper is available online. To view these files, please visit were required to be older than 17 years, with a negative pants who attended the event, with only 12% loss the journal online (http://dx.doi.​ rapid antigen diagnostic test (Ag-­RDT) on the same to follow-­up. org/10.1136/bmjopen-2021-​ afternoon, without a positive reverse-­transcription PCR ⇒ The background context of low infection rates at 058595). (RT-­PCR) or Ag-­RDT and/or symptoms associated with the time of the study and the timing of the study COVID-­19 in the previous 7 days, to not having knowingly during a previous phase of the pandemic (before the Received 27 October 2021 emergence and dominance of new variants) limit Accepted 29 April 2022 been in close contact with someone infected in the previous 10 days and to not have knowingly had close the generalisability of these findings. contact with someone with a suspicion of COVID-­19 in the previous 48 hours. A control group was paired by exact age, gender, residence municipality, socioeconomic index, where compliance with sanitary measures are previous SARS-­CoV-­2-­confirmed infection and vaccination maintainable. status, in a 1:5 ratio, from the primary care electronic health records. Primary outcome Evidence of infection at electronic INTRODUCTION health records by SARS-­CoV-­2 at 14-­day follow-­up. The SARS-­ CoV-­2 pandemic had infected Results Among the 391 participants (median age 37 186 million people and caused over 4 million years; 44% (n=173) women), no positive SARS-­CoV-­2 deaths worldwide by 12 July 2021, with wide cases were detected at 14 days, resulting in a cumulative variability between countries and regions.1 © Author(s) (or their incidence estimation of 0 (95% CI 0 to 943) per 100 000 SARS-­ CoV-­2 transmission mostly occurs by employer(s)) 2022. Re-­use inhabitants. In the control group, two cases with RT-­PCR direct contact or through droplets and aero- permitted under CC BY-­NC. No test were identified, resulting in a cumulative incidence of commercial re-­use. See rights sols from an infected person located within 102.30 (12.4 to 369) per 100 000 inhabitants. and permissions. Published by Conclusions Nightlife attendance under controlled 2 m range and with exposure time of over BMJ. conditions and with a requirement for a negative Ag-­ 15 min.2 3 Indoor, poorly ventilated and For numbered affiliations see RDT was not associated with increased transmissibility crowded spaces4 where people gather are end of article. of SARS-­CoV-­2 in a pandemic context of low infection hotspots for transmission of the virus.5 Correspondence to rates. In such circumstances, secure opening of the The COVID-­ 19, caused by SARS-­ CoV-­ 2, Dr Betlem Salvador-­Gonzalez; nightlife sector was possible, under reduced capacity has an incubation period that varies from 2 ​bsalvador@​ambitcp.​catsalut.​net and controlled access by Ag-­RDT, and environments to 14 days. Among the symptomatic people, Cunillera Puértolas O, et al. BMJ Open 2022;12:e058595. doi:10.1136/bmjopen-2021-058595 1 Open access 50% develop symptoms within 5.1 days and 75% within aged 25–49 years had some vaccination, thus constituting 11.5 days.6 age ranges where legal measures were still prominent in The gold standard diagnostic test for SARS-­CoV-­2 is controlling virus transmission. the real-­time reverse-­transcription PCR (RT-­PCR), which Some studies have been carried out in Catalonia to detects viral RNA, presenting good results in terms of reli- assess the impact of relaxing legal restrictions on various ability, sensitivity and specificity.7 Although RT-­PCR can types of social activities, including indoor gigs and dining detect positive cases from the beginning of the infection passes in restaurants; although just two articles have been in symptomatic and asymptomatic people, the need for published to date,13 14 press conferences have dissemi- well-­equipped labs with specialised professionals increases nated some results on three initiatives.15 None of these the total delivery times and costs.8 In contrast, the lateral studies detected any increased risk associated with the flow immunochromatographic rapid antigen diagnostic exposures. tests (Ag-­RDTs) for SARS-­CoV-­2 can detect viral proteins The aim of the present study was to assess the impact and provide results in situ within 30 min. Although its of relaxing the state of alarm restrictions on SARS-­CoV-­2 sensitivity is below WHO recommendations, Ag-­RDTs still infections at 14 days among people attending reopened offer the possibility of quick, easy and inexpensive SARS-­ nightclub venues. CoV-­2 detection in individuals who have high viral loads and hence are at high risk of transmitting the infection to others,9 which is the relevant issue for most public health METHODS measures.10 Reobrim Sitges was a matched cohort study, performed The health and social crises subsequent to the COVID-­19 in a nightlife-­restricted area in Sitges (Barcelona, Spain) pandemic have forced many governments to deploy new on 20 May 2021. social policies and legal restrictions, mostly focused on The volunteers attending the event were recruited by reducing the spread of COVID-­19. In Spain, restrictions to convenience sampling promoted mainly through social mobility and economic activity (with temporary closure of networks by participating entities (council, guild, venues) restaurants, hotels and nightlife activities) began with the and registered through the official city council website. first state of alarm in March 2020.11 At the time of writing Inclusion and exclusion criteria for all exposure groups of the first draft of this paper, September 2021, some (formed by study volunteers and staff groups) are defined restrictions on capacity limitations and opening hours in table 1. Participants underwent their Ag-­RDTs in sched- still prevail. The balance between health and economy is uled intervals the afternoon of the event day in Sitges. The still under study in the more flexible stage at this time: Ag-­RDT was performed by trained health professionals bars, restaurants, pubs, discotheques and concert venues following manufacturer’s instructions (AllTest, Ref. ICOV-­ were still on the tightrope, claiming for secure measures 502, Japan). The manufacturer’s reported sensitivity and to allow them to flounder. specificity were 96.4% and 99.9%, respectively. Herd immunity, mainly through mass vaccination, is The nightlife event took place from 23:00 on 20 May to the key goal to restoring social and economic activities 03:00 on 21 May, in a restricted street section, including in this sector. In Catalonia, on 5 May 2021, 30.5% of the five nightclubs with indoor areas (capacity 42–98 people) population had received at least one dose, and 13.6% had and outdoor terraces (capacity 15–35 people), with completed vaccination.12 Due to age prioritisation, only controlled registered access exclusively for participants. 6.9% of Catalonian people aged 18–24 years old and 11% Mask was mandatory (surgical or FFP2), except while Table 1 Inclusion and exclusion criteria for study participants (volunteers and staff groups) attending the nightlife mass gathering event Inclusion criteria Exclusion criteria 1. Aged over 17 years 1. Declaring to have had a positive RT-­PCR or Ag-­RDT in the last 7 days 2. Living in Sitges area and Barcelona 2. Presenting symptoms associated with COVID-­19 in the last 3. Having a personal card from the Catalan public healthcare 7 days (according to Catalan Health Department protocols32 33) system ► at least one of these: fever, persistent cough, shortness of breath, anosmia, ageusia 4. A negative Ag-­RDT the same afternoon (provided by the ► at least two of the following: sore throat, a cold, fatigue, organisation) myalgia, headache, vomiting or diarrhoea stomachache 3. Having had close contact with someone infected in the last 10 days 4. Having had close contact with someone suspected to have COVID-­19 in the last 48 hours Ag-­RDT, rapid antigen diagnostic test; RT-­PCR, reverse-­transcription PCR. 2 Cunillera Puértolas O, et al. BMJ Open 2022;12:e058595. doi:10.1136/bmjopen-2021-058595 Open access Figure 1 Participant flow chart. Ag-­RDT, rapid antigen diagnostic test; EHR, electronic health record. drinking or smoking. Drinking was allowed indoors and 1.38% (six positive cases), with a significance level of 0.05 outdoors. Social distancing was not required. Hydroalco- and power of 0.8. holic gel and panels reminding about COVID-­19 safety A participant flow chart is shown in figure 1. standards and their participation in the study were distrib- uted throughout the entire area. No special ventilation Variables measures were required. A follow-­up Ag-­RDT on day 6 The main outcome was a confirmed case (PCR, Ag-­RDT after the event was performed on participants. and serology) of SARS-­CoV-­2 infection at 14-­day follow-­up. The control group was obtained through secondary As a secondary outcome, the number of positive Ag-­RDTs data from the primary care electronic health records (PC-­ performed in person at 6 days in the exposure group was EHRs), by a pseudonymised paired extraction of individ- considered. The main outcome for the exposure group uals not attending the social event. Pairing was executed was gathered from both the 6-­day follow-­up Ag-­RDT and by exact age, gender, residence municipality, socioeco- any registry in the PC-­EHR at 14-­day follow-­up and for the nomic index, previous SARS-­CoV-­2-­confirmed infection control group only from PC-­EHR. and vaccination status (at least one dose administered), in a 1:5 ratio. All other variables were obtained from PC-­EHR: age, Sample size was conditioned on capacity limitations gender, MEDEA socioeconomic deprivation index16 established at 75% of the venue’s usual limits (according (classifying individuals into septiles), previous SARS-­ to and authorised by the health department within the CoV-­2-­confirmed infection and previous vaccination: first context of this study), resulting in 400 volunteers. Consid- and second intake, date and vaccine commercial brand ering the 14-­ day cumulative incidence of COVID-­ 19 (BioNTech-­Pfizer/Moderna/Oxford AstraZeneca/ occurring in the health district (Gerència Territorial Janssen-­Johnson&Johnson). Metropolitana Sud) on 29 April 2021 (210/100 000 This information was collected for all participants, who inhabitants12), significant differences would be found were classified according to their role as organisers, secu- observing a 14-­day incidence in the intervention group of rity personnel, club workers or volunteers. Cunillera Puértolas O, et al. BMJ Open 2022;12:e058595. doi:10.1136/bmjopen-2021-058595 3 Open access Statistical analysis No positive SARS-­CoV-­2 cases were detected at 14 days All variables were described and compared by partici- in the exposure group (estimated cumulative incidence pant role groups. Median, IQR, mean and SD were calcu- (95% CI): 0 (0 to 943)/100 000 inhabitants) and two posi- lated for continuous variables, and absolute and relative tive RT-­PCR cases in the control group (cumulative inci- frequencies were described for categorical variables. dence of 102 (12.4 to 369)/100 000 inhabitants). Homogeneity in distribution across roles was tested using Kruskal-­Wallis or Χ2 tests and complete case analysis. As pairing was performed by the exact characteristics, no description is provided for the controls (presenting the DISCUSSION same values as study participants). Key results Cumulative incidence was calculated for study partici- The Reobrim Sitges nightlife study loosening state of pants as the number of positive cases at 14 days divided by alarm restrictions in small clubs resulted in no positive the total of individuals exposed, transformed into cases SARS-­CoV-­2 test results among participants at the 14-­day per 100 000 inhabitants and with CIs estimated by the follow-­up, while two positive cases were detected in the exact method. control group without statistically significant differences. This study adds new evidence to other studies assessing Patient and public involvement the impact of reopening the social and cultural nightlife. The Associació d'Establiments d'Oci Nocturn de Sitges (Association of Nightlife Premises of Sitges) and the Comparison with previous studies Federació Catalana de Locals d'Oci Nocturn (Catalan To date, most articles studying COVID-­19 in mass gath- Federation of Nightclubs) proposed and promoted the ering events either reported retrospective analyses of initiative and developed the initial proposal together with SARS-­CoV-­2 transmission17–19 or described mitigation the Sitges Council. The Catalan Public Health Agency was plans and measures applied during mass gathering contacted to adapt it to a formal study design and develop events.20 21 Only one controlled trial was published in it, with the aforementioned entities participating in the Catalonia.13 conception and dissemination. The results were returned Revollo et al13 present a randomised controlled trial immediately to the entities for their dissemination. assessing the impact, in terms of SARS-­CoV-­2 infections, of attending a live gig in a medium-­sized concert hall (capacity for 900 people) in Barcelona, in December RESULTS 2020. One thousand forty-­seven individuals aged 18–59 No positive Ag-­RDTs were detected at baseline. The final years with a negative Ag-­RDT on the same day, no comor- exposure group included 391 participants (332 volun- bidities and declaring not to have had a positive COVID-­19 teers, 9 security staff, 32 bartenders/DJs, 18 organisers) diagnosis during the last 14 days were randomly assigned who accessed the restricted nightlife area. Participants had to the experimental group and attended the indoor event a median/mean age of 37/37.5 years, 50% were between (at 50% of venue’s capacity; n=465), or sent home (control 23 and 50 years (table 2). A total of 55.8% (n=218) were group, n=495). With a mean staying time of 2:40 hours, male, and there was an under-­representation of extreme 8 days after the event no positive RT-­PCR tests were found Catalan socioeconomic ranges (especially the least in the intervention group, whereas two (<1%) individuals deprived, with a 4.1% in front of the 28.6% in the general in the control arm had a positive Ag-­RDT and RT-­PCR population). About 9.0% (n=35) had previously been results. Common elements in this study are: sample size, infected by SARS-­CoV-­2, 10.7% (n=42) had at least one use of Ag-­RDT as inclusion criterion, age ranges, freedom vaccination dose and 19.7% (n=73) had been vaccinated of movement with no social distance and use of masks as well as infected. (although FFP2 and surgical masks were allowed in this Staff groups were significantly different from volun- study). Both studies obtained similar results, although in teers in terms of age (organisers were significantly older), this study, (a) drinking was allowed in the entire perim- gender (due to a 100% male security personnel) and eter and (b) the event was held in venues with indoor socioeconomic status (55.5%–five of security personnel capacities below 100 people without indoor air quality came from most deprived areas). Although not signifi- control and with larger outdoor areas. cant, security personnel and bartenders/DJs had lower In March 2021, an observational study assessed the vaccination and previous infection percentages. As the impact of attending a live gig in a large concert hall in control group was matched by exact characteristics, it Barcelona: 4584 attendees (below 30% of the hall’s 17 presented exactly the same distribution for all variables 000 person capacity) with negative Ag-­RDT simultane- except for the outcomes. ously enjoyed the experience in three isolated groups. Volunteers stayed in the restricted nightlife venue No social distancing and wearing of FFP2 masks were area for a mean of 177 min (minimum–maximum: required and independent drinking areas were estab- 59–210 min). Three hundred seventy-­three (88%) partic- lished. The result was a cumulative incidence at 14 days ipants attended the 6-­day Ag-­RDT, all of them with nega- of 131 infections per 100 000 inhabitants. This, compared tive results. with the age-­adjusted estimation of 296/100 000 observed 4 Cunillera Puértolas O, et al. BMJ Open 2022;12:e058595. doi:10.1136/bmjopen-2021-058595 Table 2 Sample characteristics and outcomes, overall and by subgroup Security personnel Study participants n Missing Global Organisers (n=18) (n=9) Club workers (n=32) (n=332) P value Age: median (IQR) 391 0 37.00 (23.00–50.00) 54.00 (48.25–57.00) 41.00 (38.00–46.00) 29.00 (25.00–40.25) 35.50 (23.00–50.00) <0.001 Age: mean (SD)     37.54 (15.53) 51.67 (8.60) 41.44 (6.95) 33.06 (10.53) 37.10 (15.99) <0.001 Gender: n (%) 391 0 0.017  Women     173 (44.25) 8 (44.44) 0 (0.00) 10 (31.25) 155 (46.69)    Men 218 (55.75) 10 (55.56) 9 (100.00) 22 (68.75) 177 (53.31) MEDEA deprivation index: median (IQR) 374 17 −0.32 (−0.32 to 0.48) −0.32 (–0.32 to –0.14) 0.64 (0.48–1.07) −0.32 (–0.32 to 0.64) −0.32 (–0.32 to 0.48) 0.022 MEDEA deprivation index: mean (SD) 0.04 (0.59) −0.03 (0.64) 0.79 (0.49) 0.09 (0.67) 0.02 (0.58) 0.015 MEDEA deprivation index categories: n (%) 391 0           <0.001  Least deprived septiles (28.6%) 16 (4.09) 0 (0.00) 0 (0.00) 1 (3.12) 15 (4.52)  Most deprived septiles (28.6%)     98 (25.06) 3 (16.67) 5 (55.56) 9 (28.12) 81 (24.40)    3 central septiles (42.8%) 260 (66.50) 13 (72.22) 1 (11.11) 21 (65.62) 225 (67.77)  No MEDEA     17 (4.35) 2 (11.11) 3 (33.33) 1 (3.12) 11 (3.31)   Previous infection: n (%) 391 0 35 (8.95) 3 (16.67) 0 (0.00) 2 (6.25) 30 (9.04) 0.477 Previous infection date: median (IQR) 35 356 2 Nov 2020 (17 Aug 13 Jan 2021 (4 Nov 2020– – 19 Jan 2021 (2 Jan 2021– 15 Oct 2020 (12 Aug 0.256 2020–8 Jan 2021) 17 Jan 2021) 5 Feb 2021) 2020–3 Jan 2021) First vaccination: n (%) 391 0 42 (10.74) 1 (5.56) 0 (0.00) 2 (6.25) 39 (11.75) 0.456 Vaccine 1 company: n (%) 42 349              BioNTech/Pfizer 17 (40.48) 1 (100.00) – 0 (0.00) 16 (41.03) Cunillera Puértolas O, et al. BMJ Open 2022;12:e058595. doi:10.1136/bmjopen-2021-058595  Moderna     8 (19.05) 0 (0.00) – 2 (100.00) 6 (15.38)    Oxford/AstraZeneca 17 (40.48) 0 (0.00) – 0 (0.00) 17 (43.59) Second vaccination: n (%) 391 0 23 (5.88) 1 (5.56) 0 (0.00) 2 (6.25) 20 (6.02) 0.900 Vaccine 2 company: n (%) 23 368  BioNTech/Pfizer     15 (65.22) 1 (100.00) – 0 (0.00) 14 (70.00)    Moderna 7 (30.43) 0 (0.00) – 2 (100.00) 5 (25.00)  Oxford/AstraZeneca     1 (4.35) 0 (0.00) – 0 (0.00) 1 (5.00)   Vaccinated and infected: n (%) 391 0 73 (18.67) 4 (22.22) 0 (0.00) 3 (9.38) 66 (19.88) 0.225 Follow-­up Ag-­RDT at 6 days: n (%) 391 0           0.069  Negative result 344 (87.98) 17 (94.44) 6 (66.67) 31 (96.88) 290 (87.35)  Not attending     47 (12.02) 1 (5.56) 3 (33.33) 1 (3.12) 42 (12.65)   Extra tests at 14 days: n (%) 18 373 –  RT-­PCR     13 (72.22) – 2 (100.00) 2 (100.00) 9 (64.29)    Ag-­RDT 5 (27.78) – 0 (0.00) 0 (0.00) 5 (35.71) Test results at 14 days: n (%) 18 373           –  Negative result 18 (100.00) – 2 (100.00) 2 (100.00) 14 (100.00) Ag-­RDT, rapid antigen diagnostic test; RT-­PCR, Real-­time Reverse-­Transcription Polymerase Chain Reaction. Open access 5 Open access in the city of Barcelona for the same period, had no signif- exclusively with mandated use of masks. The dissonance icant impact due to the event,14 in line with our results. between the results of controlled studies and real life, As mentioned previously, the press has published other apart from the higher transmissibility of the Delta variant, experiences such as the ‘Obrir Girona’ initiative,15 from highlights the importance of access control and sanitary 23 April to 22 May 2021 in Girona, assessing the impact measures when reducing the spread of the virus. of reactivating a broader range of social activities under Despite Ag-­ RDT lacking high sensitivity,9 evidence ‘very low infection capacity’ conditions. Social activities supports its use, along with other measures, to ensure included dinners in restaurants, an electronic music gig safe enough environments for mass gathering (nightlife) (250 attendees at full capacity, wearing masks–drinking events; a low-­cost, easy performance and quick-­result test allowed in independent room–with no social distancing) seems a good option for a wide range of social activities. and a pop gig (1000 attendees at 56% capacity, wearing Nonetheless, the use of Ag-­RDT needs to be evaluated in masks–drinking allowed at outdoor bar–with no social every situation depending on the type of activity and the distancing). ‘Very low infection capacity’ was considered epidemiological data at the time of the event, including if participants were vaccinated in the last 6 months, had vaccination rate.30 Each real situation needs to balance overcome COVID-­19 in the last 3 months or had a nega- the benefits of having rapid Ag-­RDT results for imme- tive Ag-­RDT in the last 36 hours. Of the 1350 participants, diate and appropriate management and public health only 3 had a positive test between day 7 and 14 after the action against the harm of false negative results.30 In this events.22 Remarkably, the study inclusion criteria for study, as in the two studies in Barcelona, the organisa- participants relied on Ag-­RDT screening and also consid- tion provided the tests the same day. This guarantees the ered recent vaccination or infection as an indicator of temporal proximity to the event and the inalterability low infection capacity. Despite its heterogeneity in social of results, although logistic, sanitary and economic activities and locations, the observed low incidence rate resources are required, which could be feasible for large supports their low infection capacity criterion. events but not so much for nightlife in small clubs. Addi- Other projects have been undertaken in the Nether- tionally, performing tests does not exclude the neces- lands and UK to examine how events can be reopened sity to follow other safety measures, such as mask use.24 with reduced risk.23 24 Fitzgerald et al25 explored the Applications in line with the ‘Re-­open EU’ or the one management of COVID-­19 restrictions to operate safely used in the ‘Obrir Girona’ study can be a useful tool in licensed premises. Physical distancing, which was not for reporting low infection capacity probability from required in this study, was one of the more challenging different sources. aspects. A pilot study in Liverpool explored nightclubs The highly variable context/situation hinders the reopening in semicontrolled settings.26 Despite differ- reproducibility of these types of studies. The extension ences in the methodology, the results were in line with of vaccination to all age ranges along with sanitary access ours; an exploratory modelling of transmission risk control to nightlife activities should provide a safer at nightclubs suggests that primary transmissions are nightlife environment, necessary to recover social and reduced by 53% through testing on the day. Informally, if these unpublished results were correct, economic activities, while discouraging uncontrolled social activities in Catalonia under sanitary controlled nightlife ‘botellón’ (street alcohol consumption) and access would have resulted in 9 people infected at 14 days illegal private mass events. out of 6739 participants to date. However, press informa- This study was performed when the first cases of tion has attributed to the three extraordinarily authorised SARS-­CoV-­2 Delta variant had been detected in Spain, festivals in Catalonia in July 2021, with an infection risk the Delta variant being around 60% more transmis- around 1.7 times higher than expected.27 28 Without an sible than the predominant Alpha variant. Although official published report, the inefficiency of the Ag-­RDT the transmissibility context was determinant to allow control process in one of the events, and the relaxation ethical approval, the results presented must be carefully in the use of masks after several hours in an environment interpreted according to the low background infection considered to be safe, along with the appearance of more rate at the time of the study. At that time, the pandemic contagious SARS-­ CoV-­2 variants, were pointed out as was in a regression phase, with a cumulative incidence possible causes for such poor results in comparison with in Catalonia at 14 days of 210 cases per 100 000 inhabi- pilot studies. This led to new limitations and highlighted tants.12 Further research is therefore needed to ensure the importance of vaccination and the cumulative protec- the results can be extrapolated to the Delta and future tive effect of Ag-­RDTs and masks in these scenarios. variants and in the different severity and transmissibility scenarios. Delta variant spread worldwide as the fittest Generalisability and fastest variant until then and it became dominant On 29 July, after a few weeks of reporting a negative evolu- in many countries. Evidence in the UK showed that 75% tion, especially in the 15–24 age range population, the of infections by Delta variant occurred in people who Catalan government decided to suppress the reopening were not vaccinated and about 4%–57% in people who of nightlife social activities.29 Such activities had been were fully vaccinated,31 thus affecting age ranges more opened until then without any sanitary access control, disposed to enjoying nightlife. 6 Cunillera Puértolas O, et al. BMJ Open 2022;12:e058595. doi:10.1136/bmjopen-2021-058595 Open access 5 Strengths and limitations Escola d’Infermeria, Facultat de Medicina i Ciencies de la Salut, Universitat de There are limitations in this study. The selection of volun- Barcelona, Barcelona, Spain 6 Subdirecció General de Drogodependències, Agència de Salut Pública de teers was non-­random (convenience sampling), with the Catalunya. Departament de Salut, Generalitat de Catalunya, Barcelona, Spain aim of including a profile of clients specific to each night- 7 Direcció, Fundació Institut Universitari per a la recerca a l'Atenció Primària de Salut club. To adjust for this selection bias, a control group Jordi Gol i Gurina (IDIAPJGol), Barcelona, Spain matched by age, gender, socioeconomic index, history of SARS-­CoV-­2 infection and SARS-­CoV-­2 vaccine status was Twitter Mercè Marzo-­Castillejo @mmarzoc and Jesús Almeda Ortega @ JAlmedaOrtega sought. However, a residual bias cannot be ruled out as a result of other parameters that cannot be controlled. Acknowledgements We would like to thank Carles Cortés, Eva Lacasta, David Alburquerque, Mercè Fernandez and the whole team of Ajuntament de Sitges Many limitations are inherent to how SARS-­ CoV-­2 (Sitges City Council) who made it possible, Damià Orts and the Associació infection is measured, given the different criteria applied d'Establiments d'Oci Nocturn de Sitges (Association of Nightlife Premises of Sitges) for intervention and control groups. At baseline, the and Glòria Cabrera and the Federació Catalana de Locals d'Oci Nocturn (Catalan intervention group received an Ag-­RDT evaluation that Federation of Nightclubs) for the advice on designing the study and dissemination, and Esther Sancho and the whole Curasana team. was not applied in the control group, which was selected according to EHR without any additional prior check-­up. Contributors OCP—study design, data analysis and manuscript drafting. SC-­M— study design and manuscript draft. MM-­C—study design and manuscript draft. Although sensitivity and specificity of the Ag-­RDTs are DLG—study design and manuscript draft. MAA—study design, data extraction and far from perfect, there is a higher probability of under- manuscript revision. JAO—study design and manuscript draft. JC—conception, estimating the presence of SARS-­CoV-­2 infection in the study design and manuscript revision. JB—conception, study design and control group (ie, having included asymptomatic or manuscript revision. BS-­G—conception, study design and manuscript draft and guarantor. All authors have approved the final version of the manuscript. mild symptomatic cases not attended by health systems Funding The Sitges Council funded the initiative (covering all test, organisation in the control group), which could reflect on a worse and security costs), relying on the Catalan Public Health Agency for its development evolution of controls. Also, evidence of infections at 14 (award/grant number not applicable). days was obtained for the volunteers and the control Competing interests None declared. group through EHR, although the intervention group Patient and public involvement Patients and/or the public were involved in the performed a follow-­up Ag-­RDT 6 days after the interven- design, or conduct, or reporting, or dissemination plans of this research. Refer to tion (with an acceptable loss rate of 12%, as compared the Methods section for further details. with similar studies in the UK earlier this year26), which Patient consent for publication Not required. complemented EHR information. These follow-­up tests Ethics approval This study was approved by the Research Ethics Committee increased the likelihood of measuring the impact of the of the Institute for Primary Health Care Research Jordi Gol i Gurina (IDIAPJGol) intervention on the onset of new infections, reducing and the Technical Committee of the Catalonia Civil Protection Plan (PROCICAT) the underestimation of asymptomatic cases identified (reference number 21/119-­PCV). The study guarantees compliance with the new General Data Protection Regulation (GDPR) (EU 2016/679), the guidelines of the through EHR at follow-­up only in the intervention group. Principles of the Declaration of Helsinki and the Belmont Report. Participants were The highly fluctuating characteristics in transmissibility informed about the project and signed a statement of compliance and informed and severity of the different variants and phases during consent to participate and allow the use of their pseudonymised data exclusively the pandemic hinder extrapolation of all studies’ find- for this project. Informed consent was not required for participants in the control group as the information was pseudonymised. The external entity 'Curasana' (​ ings to the context in which they were developed. There- www.​curasana.​org) was responsible for the logistics and for performing Ag-­RDTs. fore, aspects mentioned in the Generalisability section of The results were sent to the Catalan Institute of Health (ICS); positive results the discussion are a major limitation for this study. were communicated and entered into EHR for assistance purposes. The ICS and the IDIAPJGol were independently responsible for the data processing within the framework of this study. Provenance and peer review Not commissioned; externally peer reviewed. CONCLUSION Data availability statement No data are available. Due to ethical reasons stated In conclusion, in this study, attendance to nightclubs by the Ethics Committee, data cannot be made available. under controlled conditions and with a requirement for Open access This is an open access article distributed in accordance with the negative Ag-­RDT did not show an increased transmissi- Creative Commons Attribution Non Commercial (CC BY-­NC 4.0) license, which bility of SARS-­CoV-­2 in a pandemic context of low infec- permits others to distribute, remix, adapt, build upon this work non-­commercially, and license their derivative works on different terms, provided the original work is tion rates. These results, within the framework of health properly cited, appropriate credit is given, any changes made indicated, and the use and safety, provide insight into the possibility of safer is non-­commercial. See: http://creativecommons.org/licenses/by-nc/4.0/. openings for event organisers. ORCID iDs Oriol Cunillera Puértolas http://orcid.org/0000-0003-2891-099X Author affiliations 1 Mercè Marzo-­Castillejo http://orcid.org/0000-0002-1201-3090 Unitat de Suport a la Recerca Costa de Ponent, Fundació Institut Universitari per a Jesús Almeda Ortega http://orcid.org/0000-0002-7602-0679 la recerca a l'Atenció Primària de Salut Jordi Gol i Gurina (IDIAPJGol), Cornellà de Llobregat, Spain 2 Universitat Autònoma de Barcelona, Bellaterra (Cerdanyola del Vallès), Spain 3 Servei d'Atenció Primària Alt Penedès-­Garraf-­Baix Llobregat Nord, Direcció d'Atenció Primària Costa de Ponent, Institut Catala De La Salut, L'Hospitalet de REFERENCES 1 Johns Hopkins University. Center for systems science and Llobregat, Spain engineering (CSSE). coronavirus COVID-­19 (2019-­nCoV). Available: 4 Secretaria Tècnica, Direcció d'Atenció Primària Costa de Ponent, Institut Català de https://www.arcgis.com/apps/dashboards/bda7594740fd40299423​ la Salut, Cornellà de Llobregat, Spain 467b48e9ecf6 [Accessed 13 Aug 2021]. Cunillera Puértolas O, et al. BMJ Open 2022;12:e058595. doi:10.1136/bmjopen-2021-058595 7 Open access 2 Jayaweera M, Perera H, Gunawardana B, et al. Transmission of prospective open label user survey. Expert Rev Anti Infect Ther COVID-­19 virus by droplets and aerosols: a critical review on the 2021;19:1325–30. unresolved dichotomy. Environ Res 2020;188:109819. 20 Limbachia J, Owens H, Matean M, et al. Organizing a mass gathering 3 Oran DP, Topol EJ. Prevalence of Asymptomatic SARS-­CoV-­2 amidst a rising COVID-­19 public health crisis: lessons learned Infection : A Narrative Review. Ann Intern Med 2020;173:362–7. from a Chinese public health forum in Vancouver, bc. Cureus 4 Somsen GA, van Rijn C, Kooij S, et al. Small droplet aerosols in 2020;12:e12365. poorly ventilated spaces and SARS-­CoV-­2 transmission. Lancet 21 McCloskey B, Zumla A, Ippolito G, et al. Mass gathering events and Respir Med 2020;8:658–9. reducing further global spread of COVID-­19: a political and public 5 World Health Organization. Coronavirus disease (COVID-­19), health dilemma. Lancet 2020;395:1096–9. 2020. Available: https://www.who.int/emergencies/diseases/novel-​ 22 Agència Catalana de Notícies. Els impulsors d’Obrir Girona demanen coronavirus-2019/question-and-answers-hub/q-a-detail/coronavirus-​ ampliar el programa a tot Catalunya després de l’èxit de la prova disease-covid-19 [Accessed 13 Aug 2021]. - Diari de Girona, 2021. Available: https://www.diaridegirona.cat/​ 6 Lauer SA, Grantz KH, Bi Q, et al. The incubation period of coronavirus girona/2021/06/04/els-impulsors-dobrir-girona-demanen-52621652.​ disease 2019 (COVID-­19) from publicly reported confirmed cases: html [Accessed 13 Aug 2021]. estimation and application. Ann Intern Med 2020;172:577–82. 23 Dutch government. Fieldlab Evenementen, 2020. Available: https://​ 7 Wang W, Xu Y, Gao R, et al. Detection of SARS-­CoV-­2 in different fieldlabevenementen.nl/fieldlab-english/ [Accessed 13 Aug 2021]. types of clinical specimens. JAMA 2020;323:323. 24 Gov.UK. Information on the Events Research Programme - GOV. 8 Younes N, Al-­Sadeq DW, AL-­Jighefee H, et al. Challenges in UK, 2021. Available: https://www.gov.uk/government/publications/​ laboratory diagnosis of the novel coronavirus SARS-­CoV-­2. Viruses information-on-the-events-research-programme [Accessed 13 Aug 2020;12:582. 2021]. 9 World Health Organization. Antigen-­detection in the diagnosis of 25 Fitzgerald N, Uny I, Brown A, et al. Managing COVID-­19 transmission SARS-­CoV-­2 infection using rapid immunoassays, 2020. Available: risks in bars: an interview and observation study. J Stud Alcohol https://www.who.int/publications/i/item/antigen-detection-in-​ Drugs 2021;82:42–54. the-diagnosis-of-sars-cov-2infection-using-rapid-immunoassays 26 Department for Digital Culture Media and Sport - Gov.UK. Events [Accessed 13 Aug 2021]. Research Programme: Phase I findings - GOV.UK, 2021. Available: 10 Mina MJ, Peto TE, García-­Fiñana M, et al. Clarifying the evidence https://www.gov.uk/government/publications/events-research-​ on SARS-­CoV-­2 antigen rapid tests in public health responses to programme-phase-i-findings/events-research-programme-phase-i-​ COVID-­19. Lancet 2021;397:1425–7. findings [Accessed 13 Aug 2021]. 11 Ministerio de la Presidencia R con las C y MD. Real Decreto 27 Mouzo J. Los festivales de música en Cataluña aumentaron La 463/2020, de 14 de marzo, POR El que se declara El estado transmisión de la covid: más de 2.000 asistentes se infectaron. El de alarma para La gestión de la situación de crisis sanitaria País, 2021. Available: https://elpais.com/espana/catalunya/2021-08-​ ocasionada POR El COVID-­19, 2020. Available: https://www.boe.​ 04/los-festivales-de-musica-en-cataluna-aumentaron-la-transmision-​ es/buscar/pdf/2020/BOE-A-2020-3692-consolidado.pdf [Accessed de-la-covid-mas-de-2000-asistentes-se-infectaron.html [Accessed 13 Aug 2021]. 13 Aug 2021]. 12 Departament de Salut. Generalitat de Catalunya. Dades COVID, 28 Cabezas C. Roda de premsa sobre El seguiment del procés de 2021. Available: https://dadescovid.cat [Accessed 13 Aug 2021]. vacunació de la COVID-­19 a Catalunya, 31:55, 2011. Available: 13 Revollo B, Blanco I, Soler P, et al. Same-­Day SARS-­CoV-­2 antigen https://www.youtube.com/watch?v=9MUfakIxVSA&t=1915s test screening in an indoor mass-­gathering live music event: a [Accessed 13 Aug 2021]. randomised controlled trial. Lancet Infect Dis 2021;21:1365–72. 29 Diari Oficial de la Generalitat de Catalunya. RESOLUCIÓ 14 Llibre JM, Videla S, Clotet B, et al. Screening for SARS-­CoV-­2 SLT/2498/2021. Barcelona: Generalitat de Catalunya, 2021. antigen before a live indoor music concert: an observational study. Available: https://dogc.gencat.cat/ca/document-del-dogc/?​ Ann Intern Med 2021;174:1487–8. documentId=907691 [Accessed 13 Aug 2021]. 15 Catalunya CBde, CBCat OG–, 2021. Available: https://obrirgirona.​ 30 Peeling RW, Olliaro PL, Boeras DI, et al. Scaling up COVID-­19 cat/ [Accessed 13 Aug 2021]. rapid antigen tests: promises and challenges. Lancet Infect Dis 16 Domínguez-­Berjón MF, Borrell C, Cano-­Serral G, et al. [Constructing 2021;21:e290–5. a deprivation index based on census data in large Spanish cities(the 31 Public Health England. SARS-­CoV-­2 variants of concern and variants MEDEA project)]. Gac Sanit 2008;22:179–87. under investigation in England. Technical Briefing 2021;15. 17 Che Mat NF, Edinur HA, Abdul Razab MKA, et al. A single mass gathering 32 Generalitat de Catalunya. Departament de Salut. Procediment resulted in massive transmission of COVID-­19 infections in Malaysia with d’actuació enfront de casos d’infecció pel nou coronavirus SARS-­ further international spread. J Travel Med 2020;27:taaa059. CoV-­2 Sub-­direcció General de Vigil ncia i Resposta a Emergències 18 Pavli A, Smeti P, Papadima K, et al. A cluster of COVID-­19 in pilgrims de Salut Pública., 2021. Available: https://canalsalut.gencat.cat/​ to Israel. J Travel Med 2020;27:1–3. web/.content/_A-Z/C/coronavirus-2019-ncov/material- [Accessed 13 19 Shmuel K, Dalia M, Tair L, et al. Low pH Hypromellose (Taffix) nasal Aug 2021]. powder spray could reduce SARS-­CoV-­2 infection rate post mass-­ 33 Gobierno de España. Ministerio de Sanidad. Estrategia de detección gathering event at a highly endemic community: an observational precoz, vigilancia Y control de COVID-­19, 2021. 8 Cunillera Puértolas O, et al. BMJ Open 2022;12:e058595. doi:10.1136/bmjopen-2021-058595