Late Breaking Abstract - An interventional crossover study on effectiveness air cleaning on incident infections in day care

Growing scientific evidence highlights the airborne transmission in the spread of respiratory infections. However, there is no consensus on the importance of airborne infection in real-life. This study investigated the significance of the airborne transmission route and the effectiveness of air cleaning in reducing infections among children in daycare. A cross-over study was conducted in four daycare centers in Helsinki randomised in intervention-control and control-intervention sequences. All children attending the daycare were invited to participate (n = 262) and the sole inclusion criterion was that the children were expected to stay in the same day care center during the two year duration of the study. Consent was given by a guardian for 88 children of which 35 were lost to follow up resulting in 51 subjects for the final analysis. Clean air flow rate was increased by 2.1-2.9 times compared to baseline mechanical ventilation using portable air cleaners. The intervention reduced incident infections from 0.95 to 0.78 infections per child per month among the children (primary outcome) in daycare. The reduction attributed to intervention in the negative binomial regression model was 18.0 % (95% CI 2.1-31.3 %, p = 0.028). We observed a significant decrease in incident infections without implementing any other infection mitigation strategies but air cleaning. Our results challenge the current paradigm which emphasizes fomite and contact transmission and infection control measures that target these routes. As ventilation and air cleaning can only affect particles able to float in the air stream, our results support the significance of airborne transmission among respiratory pathogens.