Interventions used to improve air flow in hospitals – a rapid review

The COVID-19 pandemic has highlighted the need for improved air flow in hospitals, to reduce the transmission of airborne infections such as COVID-19. The aim of this review was to map the existing literature on intervention used to improve air flow in hospitals, understanding challenges in implementation and the findings of any evaluations. We reviewed peer-reviewed articles identified on three databases, MEDLINE, Web of Science and the Cochrane Library with no restriction on date. 5846 articles were identified, 130 were reviewed and 18 were included: ten articles were from databases and eight articles were identified through hand searching. Results were discussed in terms of three categories: (i) concentration of aerosol particles, (ii) changes in/effect of air speed and ventilation and (iii) improvements or reduction in health conditions. Eight studies included an evaluation, the majority only had one comparator condition however three had multiple conditions. The most common device or method that was outlined by researchers was HEPA filters, which can remove particles with a size of 3 microns. Articles outline different interventions to improve air flow and some demonstrate their effectiveness in terms of improving health outcomes for patients, they also suggest either mechanical and natural ventilation are the best methods for dispersing particulate matter as well as perhaps two air cleaning units rather than one. With different methods comes different strengths and weaknesses however, the key finding is that air flow improvement measures reduce the likelihood of nosocomial infections. ### Competing Interest Statement The authors have declared no competing interest. ### Funding Statement This study was funded by: LBL is supported by the National Institute for Health Research University College London Hospitals Biomedical Research Centre, and by the Wellcome/EPSRC Centre for Interventional and Surgical Sciences (WEISS) at UCL. As this research was funded in whole, or in part, by the Wellcome Trust [Grant number 203145/Z/16/Z], for the purpose of Open Access, the author has applied a CC BY public copyright licence to any Author Accepted Manuscript version arising from this submission. ### Author Declarations I confirm all relevant ethical guidelines have been followed, and any necessary IRB and/or ethics committee approvals have been obtained. Yes I confirm that all necessary patient/participant consent has been obtained and the appropriate institutional forms have been archived, and that any patient/participant/sample identifiers included were not known to anyone (e.g., hospital staff, patients or participants themselves) outside the research group so cannot be used to identify individuals. Yes I understand that all clinical trials and any other prospective interventional studies must be registered with an ICMJE-approved registry, such as ClinicalTrials.gov. I confirm that any such study reported in the manuscript has been registered and the trial registration ID is provided (note: if posting a prospective study registered retrospectively, please provide a statement in the trial ID field explaining why the study was not registered in advance). Yes I have followed all appropriate research reporting guidelines, such as any relevant EQUATOR Network research reporting checklist(s) and other pertinent material, if applicable. Yes All data produced in the present study are available upon reasonable request to the authors All data produced in the present work are contained in the manuscript * ACH : Air change per hour ACU : Air cleaning unit AFU : Air filtration unit eUVGI : Enhanced ultraviolet germicidal irradiation HEPA : High efficiency particulate air HSCT : Hematopoietic stem cell transplantation HVAC : Heating ventilation and air conditioning IA : Invasive aspergillosis ISO : Isolation room NICU : Neonatal intensive care unit PAC : Precision air conditioning PECO : Photo electrochemical oxidation PM : Particulate matter SARS-CoV-2 : Severe acute respiratory syndrome coronavirus 2