Natural ventilation, low CO2 and air filtration are associated with reduced indoor air respiratory pathogens

Currently, the real-life impact of indoor climate, human behavior, ventilation and air filtration on respiratory pathogen detection and concentration are poorly understood. This hinders the interpretability of bioaerosol quantification in indoor air to surveil respiratory pathogens and transmission risk. We tested 341 indoor air samples from 21 community settings for 29 respiratory pathogens using qPCR. On average, 3.9 pathogens were positive per sample and 85.3% of samples tested positive for at least one. The number of detected pathogens and their respective concentrations varied significantly by pathogen, month, and age group in generalized linear (mixed) models and generalized estimating equations. High CO2 and low natural ventilation were independent risk factors for detection. CO2 concentration and air filtration were independently associated with their concentration. Occupancy, sampling time, mask wearing, vocalization, temperature, humidity and mechanical ventilation were not significant. Our results support the importance of ventilation and air filtration to reduce transmission. ### Competing Interest Statement The authors have declared no competing interest. ### Funding Statement The study was financed through internal KU Leuven funds. JR acknowledges support of the Research Foundation Flanders (FWO, grant number: 1S88721N). The manufacturers of the air sampling and filtration devices were not involved in the design, conduct, analysis, or manuscript writing. The AerosolSense active air samplers, AerosolSense Capture Media and Blue PURE 221 devices were purchased. The Philips 3000i devices were donated by the manufacturer. ### Author Declarations I confirm all relevant ethical guidelines have been followed, and any necessary IRB and/or ethics committee approvals have been obtained. Yes The details of the IRB/oversight body that provided approval or exemption for the research described are given below: Ethics committee/IRB of University Hospitals Leuven / KU Leuven gave ethical approval for this work. I confirm that all necessary patient/participant consent has been obtained and the appropriate institutional forms have been archived, and that any patient/participant/sample identifiers included were not known to anyone (e.g., hospital staff, patients or participants themselves) outside the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 and uploaded the relevant EQUATOR Network research reporting checklist(s) and other pertinent material as supplementary files, if applicable. Yes All data produced in the present study are available are added in supplementary file source-file.xlsx.