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HomeMy WebLinkAboutBMJ Open Open access Original research BMJ Open Effect ofportable HEPA filters on Ps C- Scut, , 0 a co COVID-19 period prevalence: an goCC observational quasi-interventional `(Iz�12� 0 study in German kindergartens Q a) CD O Timo Falkenberg ,' Felix Wasser,' Nicole Zacharias,' Nico Mutters ,' co Thomas Kistemann1'2 a 3 `o' a co = To cite:Falkenberg T,Wasser F, ABSTRACT N Zacharias N,et al Effect Objectives The aim of the study was to evaluate the STRENGTHS AND LIMITATIONS OF THIS STUDY ro of portable HEPA filters on effect of high-efficiency particulate air(HEPA)filters on = Evaluation of high-efficiency particulate air filter's b COVID-19 period prevalence: COVID-19 period prevalence in kindergartens. effect on actual COVID-19 period prevalence. N an observational quasi Design The observational study follows an intervention = Inclusion of all children of the studied kindergartens. op interventional study in German Data are on the institutional level without further in- kindergartens.BMJ Open design with the intervention group using HEPA filters and 2023;13:e072284.doi:10.1136/ the control group not. formation on the cases. ww c. bmjopen-2023-072284 Setting The study was conducted in 32(10 intervention, = The intervention group was preselected(no random c 22 control)kindergartens(daycare centres)in Rhineland group allocation). ,'Z' ► Prepublication history for Palatinate(Germany). No this paper is available online. Participants Data of 2360 children(663 intervention,1697 ND w To view these files,please visit the journal online(httpi/dx.doi. control)were reported by the kindergarten heads.Data o 9/ I p were collected on institutional level without anyidentifyingresulted in immense social and economic o or 10.1136/bm'o en-2023 072284). information on individuals.Thus,all children of all facilities were problems. A particular challenge was the 5 included;however,no demographic data were recorded. closure of schools,kindergartens and daycare a a. NM and TK are joint senior Interventions The study followed a quasi-interventional centres, as these not only deprived the chil- a authors. design,as no formal intervention was conducted.A charity dren of education and essential social contact, 0 Received 30 January 2023 foundation equipped kindergartens with HEPA filters.These but also placed a high burden on parents and B Accepted 18 July 2023 kindergartens were enrolled as intervention group.The control other caregivers. In Germany, reopening _ group was recruited from the neighbouring communities and schools and kindergartens had a high pout- districts. ical, social and economic priority, while also 3 Outcome measures The primary outcome measure was trying to avoid children becoming spreaders -oa the number of COVID 19 cases reported by the kindergarten of the disease. SARS-CoV-2 is an airborneCD heads,converted into period prevalence rates per 1000 pathogen that can spread via three releCr - 2. population. Results The mean COVID-19 period prevalence rates of the Want routes: directly via droplets, indirectly o control and intervention groups were 186(95%CI:137.8 to via fomites and via airborne transmission, 2 238.9)and 372(95%CI:226.6 to 517.6)per 1000 children, that is, aerosols that remain in the ambient o respectively.The one-sided Wilcoxon rank-sum test indicates air for prolonged periods.' In enclosed o a p value of 0.989;thus,the hypothesised preventive effect of indoor environments, where close interac- m A Check for updates HEPA filters could not be confirmed in the kindergarten setting. tion occurs over longer periods, the highest 3 Conclusions While HEPA filters can significantly reduce the risk of contagion is evident.- Reopening m ©Author(s)(or their viral load in room air,this does not lead to reduced COVID-19 of schools and kindergartens was there- N) employer(s))2023.Re-use permitted under CC BY-NC.No prevalence in the selected kindergartens in Germany.It is fore only possible under strict hygiene and 0 commercial re use.See rights known that contagion mainly occurs via direct face-to-face N and permissions.Published by air exchange during play and that the contaminated air does prevention measures, including wearing of o- BMJ. not necessarily pass through the filter prior to air exchange personal protective equipment(PPE) (panic ro between children.The use of HEPA filters mayalso lead to a ularly facemasks), regular ventilation (every c 'Institute for Hygiene and Public 0 Health,University Hospital Bonn, sense of security,leading to reduced preventive behaviour. 30 min), mass testing and social distancing Bonn,Germany through reductions in group size. While 2Department of Geography, these measures could be enforced quite well m University of Bonn,Bonn, BACKGROUND in schools with older children, for kinder- co Germany The COVID-19 pandemic has caused severe garten children (aged 1-6 years), particu ct - cr Correspondence to disruptions of everyday public activities across larly wearing masks all day, was difficult to Dr Timo Falkenberg; the globe. Different degrees and duration of enforce. Kindergarten in Germany is defined o timo.falkenberg©ukbonn.de lockdowns and restrictions on public life have as a facility for the care and promotion of the c• BM) Falkenberg T,et al.BMJ Open 2023;13:e072284.doi:10.1136/bmjopen-2023-072284 1 Open access a co development of children of preschool age,that is,daycare use portable HEPA filters should show lower COVID-19 K centre. Whereas regular or even constant ventilation is incidences compared with those not having such filters. 0 easily realised during the warmer month; however, once This study aims to fill an important knowledge gap a) temperatures drop into the single digits, frequent venti- between the theoretical and experimental value of using _.: lation is unlikely. Therefore, spending prolonged time HEPA filters in kindergartens and schools and their actual 7/3 periods in confined indoor spaces with a large number epidemiological effect. Providing such filters in public c cr of people will place them at risk of infection.A potential facilities prompts a significant financial investment, thus solution that has been widely discussed both politically requiring clear evidence. Particularly in kindergarten n and academically is the use of high-efficiency particulate settings, high mobility of children throughout the day, N air (HEPA)filters. various close interactions and suboptimal compliance j A wide range of HEPA filters and configurations exists with hygiene measures create a unique situation that does J with differing removal efficiencies (see 3-5). Such filters not adhere to the experimental assumptions of previous rn can be installed in existing air conditioning systems and studies. are also available as portable air filters.Generally,the effi- o ciency of the filter is the same in centrally installed and a) portable devices; however,with portable filters, the posi- METHODOLOGY o tioning of the filter in the room as well as the correct use Our study used an interventional design with the inter- w are stated as critical factors and need to be considered.e 7 vention group consisting of kindergartens equipped with b HEPA filters in compliance with ISO 29463-18 guarantee portable HEPA filters and the control group not using N co the removal of at least 99.95% of particles between 0.1 any air filters. The intervention group was equipped and 0.3pm.9 The size and power of the HEPA filter will with DEMA airtech air purifiers.!" The specific units o determine the removal rate,with larger systems filtering were either AP-160, AP-120, AP-90 or AP40, adapted to o larger volumes of air.10 Manufacturers specify the clean air the room size. The DEMA-airtech system uses a coarse c delivery rate,which is the volume of air passing through prefilter,HEPA H13 filter,activated carbon filter,plasma, N the system per minute multiplied with the removal rate. titanium dioxide photocatalyst filter and ultraviolet-C w This needs to be considered in regard to the room size in light, in this order of configuration. The devices are o which the device shall be used.l certified and tested with a removal efficiency of 99.99%. o Different experimental studies have been performed to The optimal positioning and required size were decided c test the potential of HEPA filters to reduce or even elim- in discussion with the manufacturer and the head of a inate the propagation of SARS-CoV-2. The majority of the kindergartens. An independent research institute n studies did not use the actual SARS-CoV 2 in their exper- (SGS Institut Fresenius) conducted experimental tests o iment but used aerosols,bacteria or viruses of similar size in selected kindergartens, which simulated an infected 3 as surrogate particles (eg, 6-11). A more recent experi- person dispersing aerosols into the room air and found . ment confirmed that the infectious SARS-CoV 2 is effec- that after 4-9 min, the aerosol concentration was halved, a tively removed by HEPA filters; however, the authors while after 15-30min, reductions of 90% were achieved. 2. note airflow is important to consider as air does not pass All group rooms, common areas, staff rooms and m through the filter evenly±`A systematic review13 explored entrance areas were equipped, if existing also activity cr the efficiency of portable HEPA filters,highlighting that rooms (gymnasium) and sleeping rooms were equipped. 3. all reviewed studies indicated a significant reduction Consequently,all rooms and areas where multiple people 8 in airborne particles. An experiment by Curtius et all interact with each other were equipped with appropri- conducted in classroom settings using four HEPA filters ately sized devices. The air filters were installed between o highlighted that the filters significantly reduce concen- July and September 2021 and were thus fully operational o trations in between ventilation periods, however, should during the Omicron pandemic wave. be used in addition to ventilation, rather than replacing o- other preventive measures. Kahler et a114 stated that the Sample sizes m i. position of the air purifier in the room is a critical factor. Ten kindergartens in the German Federal State Rhine- ND It is unquestionable that HEPA filters effectively remove land Palatinate were equipped with the above-mentioned o particles from the air,as these filters are tested according HEPA filters forming the intervention group. In these w cr to ISO standards,and various experiments demonstrated 10 kindergartens, 663 children were cared for by 147 the effective removal of aerosols. However, no study to childcare workers in 35 groups. The intervention group c date has assessed the impact of HEPA filters on the actual was selected purposively,as these were equipped with air c. COVID-19 incidence. filters by a local charity foundation (Else-Schutz Stiftung). In our study,we assess the epidemiological effectiveness The control group kindergartens (n=22) were recruited m of portable HEPA filters in a real-life setting,investigating from neighbouring villages and districts. Next to active m the COVID-19 period prevalence in kindergartens with recruitment, the study was also announced in the local u portable air filters as compared with kindergartens that newspaper,calling on kindergartens to participate in the c, do not use them.Assuming that the HEPA filters are oper- study.The 22 kindergartens of the control group consist K ated correctly,it is hypothesised that kindergartens which of 1697 children and 374 caretakers, organised into 65 cn c- 2 Faikenberg T,etal.BMJ Open 2023;13:e072284.doi:10.1136/bmjopen-2023-072284 A aOpen access Table 1 Sample population wave, that is, November 2021 until end of May 2022. For co each group, period prevalence rates were calculated by p Group Institutions Groups Children Caretakers dividing the number of cases by the total number of chil- m Intervention 10 35 663 147 dren and multiplying the result by 1000 to produce the R Control 22 65 1697 374 prevalence rate: cases per 1000 children. Here it should be noted that all cases were summed over the time period; a therefore,a period prevalence is reported.These period t groups (see table 1). Therefore, the total sample size of Prevalence rates were then compared between the inter- Q vention and control groups using a one-sided Wilcoxon o the study was 32 kindergartens with 2360 children and co 521 childcare workers. This sample size is far beyond the rank-sum test with continuity correction. This test was o j calculated minimum required of 396 children,assuming Performed to test the hypothesis that the intervention j a 15%difference of population proportions,a 99%confi- group, that is, kindergartens with portable HEPA filters, rn dence level and a 5% margin of error. In total, kinder- have lower period prevalence than the control group. 2 gartens of three districts were enrolled into the study; Essentially, testing if a preventive effect of the HEPA filters is observed. A non-parametric test was chosen, as m the three districts did not exhibit significantly different 7 the data were not normally distributed (Shapiro-Wilk test r COVID-19 incidences at the population level and are also 0 similar in demographic and social structure. was significant). Additionally, differences between the w two groups in preventive measures were tested using Fish- b Methods er's exact test for binary variables or X2 test for categorical N co The study collected data on the institutional level with variables.Statistical significance was considered at p<0.05. . the head of the kindergartens serving as respondent.Due a to the mandatory reporting requirement to the health Patient and public involvement o authority,data accuracy can be assumed.The data collec- Patients or the public were not involved in the design, a lion involved two instruments: a baseline survey and reporting or dissemination of the research. N continuous case documentation. Both instruments were rev w self-administered and conducted online. The data entry mask was hosted on university servers, and each institu- RESULTS o tion received a username and password for data entry. The sample population included children of 32 kinder- = The baseline survey focused on establishing the number gartens. The 2360 children were divided into 663 chil- a of children and childcare workers, prevention measures dren in the intervention group,that is,with HEPA filters, a and previous COVID-19 cases in the kindergarten.Among and 1697 children in the control group, that is, without o the prevention measures, facemask wearing, ventilation HEPA filters (see table 1). Throughout the reporting 3 frequency,surface decontamination frequency and group period,the number of children remained constant. intermixing were included. Additionally, it was estab- In the majority of kindergartens (94%),facemasks were a lished when the HEPA filters were installed and in which worn outside of the group setting,that is,in the hallways 3. rooms of the individual kindergarten. The retrospective and common areas.During the actual childcare activities, m COVID-19 cases were reported according to the waves which are occurring in the group setting, only 25% of 0 of the pandemic: wave I (March-April 2020), summer kindergartens indicated childcare workers wearing face- 3 plateau 2020 (May-September 2020), wave II (October masks.Consequently,in the remaining 75%of kindergar- o 2020-February 2021), wave III (March-May 2021), tens during the majority of time spent in the kindergarten, 3 summer plateau 2021 (June-October 2021) and wave IV no facemasks were worn. No difference between control oo (November 2021-March 2022). The baseline survey was and intervention kindergartens is evident (see table 2). o conducted between 24 March and 11 April 2022.Starting In 72% of kindergartens, group allocation was fixed, m` from 8 April 2022, the continuous case documentation that is,children were always in the same group and groups m was initiated,which was continued until March 2023.This were not intermixed. However, only in 6% of kindergar- - N.) instrument involved the documentation of all COVID-19 tens group intermixing was also prohibited outside, that cases occurring in the individual kindergarten.The docu- is,during break time occurring outdoors.In these 6% of oN mentation has been conducted in 14-day intervals, with kindergartens, outdoor playtime was staggered, so that w automated reminders sent to the kindergarten heads on individual groups did not mix at all. Contact between Friday mornings. In the documentation, the numbers of childcare workers responsible for different groups was C newly infected children and childcare workers during restricted in 65% of kindergartens. No significant differ- the respective 14-day period were reported.Additionally, ence was observed between the control and intervention groups (see table 2). closure of the facility, due to quarantines, holidays or P m similar reasons were noted. Ventilation forms a key preventive measure against m contagion; 81% of kindergartens ventilated the group a Analysis rooms once per hour. About 18% of the control group As the HEPA filters were only operational starting from ventilated the group rooms more frequently, that is, K September 2021,this paper only reports on the Omicron once every 30 min,while 20% of the intervention group cs 3 Falkenberg T,et al.BMJ Open 2023;13:e072284.doi:10.1136/bmjopen-2023-072284 3 Open access a w Table 2 Facemask wearing and group intermixing presented in table 5.The period prevalence of the entire F. sample population was 236 per 1000 children for the 0 Variable Group Yes No Fisher's exact test time period (November 2021-May 2022). In the control Wearing Intervention 8 2 p=0.091 group, the period prevalence ranged from 0 to 540 per facemask Control 22 0 CI:0.00;2.32 1000 children,while the period prevalence ranged from F outside of 120 to 869 per 1000 children in the intervention group. C group The mean COVID-19 period prevalence rate was 372 and cr Wearing Intervention 2 8 p=1.000 186 per 1000 children in the intervention and control a facemask Control 6 16 CI:0.05;5.03 groups, respectively. The one-sided Wilcoxon rank-sum y during test indicates a p value of 0.989 and a CI from -oo to i childcare in 299.7.The period prevalence per 1000 childcare workers o Fred group Intervention 5 5 p=0.096 (table 6) presents similar results. In the control group, rn allocation Control 18 4 Cl: 0.03;1.54 the mean prevalence for the period from November 2021 to May 2022 was 529 per 1000 childcare workers,while it o Outdoor Intervention 1 9 p=0.534 reached 1193 per 1000 childcare workers in the interven- intermixing of Control 1 21 CI:0.03; 191.39 tion group.The one-sided Wilcoxon rank-sum test failed 7 0 groups to reach significance. Therefore, no significant preven- w Contact Intervention 5 5 p=0.252 Live effect of the HEPA filters could be found. 6 between Control 6 16 Cl:0.43;16.40 N childcare co workers DISCUSSION o Our study showed no significant preventive effect on o ventilated their group rooms less frequently,that is,every COVID-19 period prevalence in the kindergarten setting. c 2-3 hours. The X2 test indicates a significant difference This finding may be rather surprising, as various exper- ry z in the pattern of ventilation between the intervention imental studies have demonstrated the effectiveness oN and control groups with more frequent ventilation in the of HEPA filters in reducing aerosol concentrations in a control group (see table 3). enclosed rooms.It is,however,important to note that the o Surface decontamination was practised in 84% of the experimental setting is limited in imitation transmission o kindergartens; however, the frequency of decontamina- processes." The effectiveness of HEPA filters to remove 0 tion differs. On average, the surface decontamination bacteria, viruses, allergens and other aerosols from the n frequency is higher among the control group.The X2 test air is, however, not placed in question here. Neverthe- o revealed a significant difference in the pattern of surface less, such removal does not necessary reduce contagion 3 decontamination between the intervention and control between individuals situated in an enclosed room over -a groups, with a larger proportion of the control group prolonged periods of time,in particular if other measures having practised more frequent surface decontamination such as mask wearing is not possible.Furthermore,while o (see table 4). HEPA filtering systems certainly can decrease aerosol m Figures 1 and 2 depict the period prevalence for the concentrations, direct transmission via larger droplets a different COVID-19 waves for children and childcare still occurs. Hence, air circulation, person density, mask 3 workers,respectively.It is important to note that although Wearing and activity type conducted in the room are very 0 the control and intervention groups are segregated likely to affect the risk of infection and consequently the throughout the time period, the HEPA filters were only epidemiological effectiveness of HEPA filters. = installed during summer 2021. Therefore, only wave 4 In the kindergarten, the children, aged 1-6 years, are o (ie, the Omicron wave) can be used to assess the effect not stationary,but continuously move through the rooms. m of the HEPA filters.Yet, the figures clearly show that for Therefore, multiple potential sources of viral emitters o both children and childcare workers, minor elevations are moving through the rooms throughout the day. The IV were noted in waves 2 and 3 without significant differ- children play with each other in close contact while not ences between the control and intervention groups. wearing PPE. Small children as investigated here have o Only during the Omicron wave a large increase in prey- no concept of general hygiene measures for preventing Q alence was noted in both groups. The COVID-19 period transmission in general. Consequently, it is highly likely '< prevalence per 1000 children for the Omicron wave is that direct air exchange and therefore potential contact m and droplet transmission occur frequently between re multiple children throughout the day. Our data demon- v Table 3 Ventilation frequency strate that in the majority of kindergartens, facemasks m Every Every Every are not worn inside the group setting, thus also child- m o. Group 30min hour 2-3hours X2 care workers are exposed to direct contagion throughout C. the day.Although it has been demonstrated in literature o Intervention 0 8 2 p=0.045 0 that the viral load in the room air is lower with HEPA -a Control 4 18 0 filters compared with a situation without HEPA filters, o• z- 4 Falkenberg T,et at BMJ Open 2023;13:e072284.doi:10.1136/bmjopen-2023-072284 8 Open access co Table 4 Surface decontamination frequency Group Multiple times per day Daily Multiple times per week Weekly No X2 a Intervention 2 2 0 3 3 p=0.001 Control 0 18 2 0 2 an air filter that is not in direct physical proximity of the adherence to preventive measures. Hammond et al' state n infected person cannot reduce the risk of transmission by in their review on portable air filters in homes and work- a) cn direct exposition.''Air filters may reduce the risk_of trans- places that the existing research lacks important evidence mission by reducing the virus burden in the air,' 1116 but regarding the effectiveness of reducing indoor transmis- are not able to stop the direct transmission if the infected sion of respiratory infections,including SARS-CoV 2. child stays in direct contact to a susceptible child or child- Consequently, there are two suspected reasons why care worker as indicated by our results.For this reason,it the expected preventative effect of HEPA filters on the appears that the use of preventive measures,such as face- period prevalence of COVID-19 could not be confirmed m masks, frequent ventilation and surface decontamina- in the kindergarten setting: (1) the close interaction tion, remain important regardless of HEPA filters being between children during play leads to direct face-to- co used.Other studies have also highlighted the importance face air exchange and direct contact,which leads to the o of combining multiple prevention measures to induce exchange of aerosols/droplets that were not previously effective protection. '' The data obtained in our study filtered through the HEPA filter; (2) the presence of the co provide some indication that the use of HEPA filters leads HEPA filters might induce a sense of security that leads to to a reduction in preventive behaviour.Lower ventilation reduced adherence to other preventive measures, such and surface decontamination frequencies were especially as frequent ventilation, surface decontamination and c noted in the intervention group. It is suspected that the wearing of facemasks. The background COVID-19 inci- N use of HEPA filters induces a sense of security among dence was considered as a confounding factor; however, the childcare workers, which might lead to a reduced no significant differences were observed between the 0 500 5- a) co o. — 450 Group 0 N Intervention 3 LELE 400 Control -0 U a 3 0 350 -o a> Q 300 3 a) u) 250 U Z o 200 3 o- m > 150 N O.. 0 100 cr a) C 11 50 -o 0 Wave 1 Summer 2020 Wave 2 Wave 3 Summer 2021 Wave 4 Q Period n Figure 1 Period prevalence of children by pandemic waves segregated by control and intervention groups. `X'represents the mean,the upper and lower lines are±1 SD(values below 0 were omitted). P. Falkenberg T,et al.BMJ Open 2023;13:e072284.doi:10.1136/bmjopen-2023-072284 5 IL Open access a W 1100 F. El.? m 1000 Group CD o Intervention a) 900 Control 0 co o c-fi' P. 800 n s 2) o cn 0 700 0 0 'Co' 600 a a) o 500 m Ca N O 400 w a) o o N a i 300 co > = f.12 200 0 c 0 100 N 'L 0 a) _ N Wave 1 Summer 2020 Wave 2 Wave 3 Summer 2021 Wave 4 0 0 0 Period s a) Figure 2 Period prevalence of childcare workers by pandemic waves segregated by control and intervention groups. 'X' Q represents the mean,the upper and lower lines are±1 SD(values below 0 were omitted). 0 3 districts. The mean 7-day incidence in the three districts occasionally be rather institutional policy than actual was 668, 726 and 801 per 100000 population over the practice.Additionally,preventive measures have changed a reporting period. Due to the mandatory reporting of throughout the pandemic; the provided information o- COVID-19 cases of the kindergarten heads to local only forms a snapshot of the measures in place in March/ m health authority, data accuracy can be assumed, and April 2022. The study relies on few central assumptions, a reporting intensity between the intervention and control which need to be verified: (1) the HEPA filters are oper- 3 groups is comparable. Further research is required to 0 explore behavioural changes associated with the use of ated adequately, (2) the position of the HEPA filters was HEPA filters, that is, qualitative interviews with child not altered from the optimal position determined during j care workers. Furthermore, the real-world effectiveness installation, (3) all COVID-19 cases were reported to the oz of HEPA filters in school settings should be explored, as kindergarten head. Despite the mandatory reporting co schools do provide a setting in which the children are requirement,it maybe possible that some parents did not cr m more stationary and may use PPE while in the classroom inform the kindergarten of their child having contracted N setting. COVID-19. Even if the above-mentioned requirements for the operation of the air filters were not met at all o Limitations times, they correspond to reality and allow an evaluation a The study relies on the kindergarten heads as informa- of the air filters in terms of their effectiveness in practice. co tion providers; therefore, the preventive measures may m Cn -D Table 5 COVID-19 period prevalence rate per 1000 Table 6 COVID-19 period prevalence rate per 1000 0 m children from November 2021 to May 2022 childcare workers from November 2021 to May 2022 m Group Mean 95%Cl Min/max N Group Mean 95%CI Min/max N Q Intervention 372.1 226.6 to 517.6 120.5/869.0 663 Intervention 1193.2 584.8 to 1801.6 312.5/3555.6 147 0 Control 186.5 137.8 to 238.9 0/540.0 1967 Control 529.7 368.9 to 690.5 0/1500 374 Q c ' 6 Falkenberg T,et al.BMJ Open 2023;13:e072284.doi:10.1136/bmjopen-2023-072284 aOpen access OD Conclusion properly cited,appropriate credit is given,any changes made indicated,and the use K In this study, the COVID-19 period prevalence of chil- is non-commercial.See:httpJ/creativecommons.org/licenses/by-nc/4.0/. 0 dren in German kindergartens was compared between ORCID iDs m kindergartens with portable HEPA filters and those limo Falkenberg http://orcid.org/0000-0001-6778-4178 without HEPA filters during the Omicron wave. It was Nico Mutters httpi/orcid.org/0000-0002-0156-9595 iii hypothesised that the HEPA filters will have a preventive c cs effect, thus leading to lower COVID-19 period preva- N• lence among the intervention group.This hypothesis was REFERENCES m Q. 1 World Health Organization.Transmission of SARS-Cov-2: rejected as the one-sided Wilcoxon rank sum test with implications for infection prevention precautions;(world health m continuity correction did not produce significant results. organization scientific brief).2020.Available:https://www.who. — o In fact, the mean period prevalence of the control group int/news-room/commentaries/detail/transmission-of-sacs-cov-2- implications-for-infection-prevention-precautions was 186per 1000 children, whereas a mean COVID-19 w 2 Tang D,Cornish P.Kang R,et al.The hallmarks of COVID-19 disease. o period prevalence of 372 per 1000 children was observed PLoS Pathog 2020;16:e1008536. in the intervention group. 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Disclaimer The funder had no influence on data collection,study design or air filters in the era of COVID-19:function and efficacy.Otolaryngol-- o. analysis,and on the reported results. Head Neck Surg 2020;163:1153-5. 11 Zacharias N,Haag A,Brang-Lamprecht R,et al.Air filtration 0 Competing interests None declared. as a tool for the reduction of viral aerosols.Sci Total Envy On 2021;772:S0048-9697(21)00022-X. a- Patient and public involvement Patients and/or the public were not involved in 12 Ueki H,Ujie M,Komori Y,et al.Effectiveness of HEPA filters at -a the design,or conduct,or reporting,or dissemination plans of this research. removing infectious SARS-Cov-2 from the air.mSphere.mSphere a Patient consent for publication Not required. 2022;7:e00086-22. 13 Liu DT,Phillips KM,Speth MM,et al.Portable HEPA Purifiers to 0 Ethics approval Ethical approval was obtained from the ethics commission of eliminate airborne SARS-Cov-2:A systematic review.Otolaryngol-- m the Medical Faculty of the University of Bonn(Lfd.no.092/22).No ethical or data Head Neck Surg 2022;166:615-22. a 14 Kahler CJ,Fuchs T,Mutsch B,et al.Schulunterricht Wahrend der protection concerns are evident.Accordingly,informed consent was obtained by SARS-Cov-2 Pandemie Welcher Konzept ist Sicher,Realisierbar 3 the information givers,that is,head of institution.All methods were carried out in and Okologisch Vertretbar?2020.Available:http://rgdoi.net/10. o accordance with relevant guidelines and regulations. 131 40/RG.2.2.11 661.56802 3 Provenance and peer review Not commissioned;externally peer reviewed. 15 DEMA.Produktubersicht.n.d.Available:https://dema-airtech.com/ o produkte/ a Data availability statement Data are available upon reasonable request.Please 16 Kahler CJ,Fuchs T,Hain R.Konen mobile Raumluftreiniger eine o contact the corresponding author for a request for data sharing. indirekte SARS-CoV-2 Infektionsgefahr durch Aerosole wirksam m Open access This is an open access article distributed in accordance with the reduzieren?Universitat der Bundeswehr Munchen,2020.Available: 3 https://www.unibw.de/Irt7/raumluftreinigerpdf a- Creative Commons Attribution Non Commercial(CC BY-NC 4.0)license,which 17 Villers J,Henriques A,Calarco S,et al.SARS-Cov-2 aerosol Si permits others to distribute,remix,adapt,build upon this work non-commercially, transmission in schools:the effectiveness of different interventions. N and license their derivative works on different terms,provided the original work is Swiss Med Wkly 2022;152:w30178. V N o N co a- co C CD Si. CD C) CD 0- CT C) 0 (E Falkenberg T,et al.BMJ Open 2023;13:e072284.doi:10.1136/bmjopen-2023-072284 7 L