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RR/ID Strength of Evidence Scale rating by reviewer: Potentially informative.

Review:  This preprint provides evidence for the effect of air cleaning with portable room air cleaners (PAC) in reduction of airborne transmission of common infections in day care units. The authors collected information through weekly electronic surveys answered by parents, and the study demonstrated clinically and statistically significant reduction in incident infections in daycares as the primary outcome, and the secondary outcome of parents’ absence from work did not reach statistical significance. The manuscript challenges the current paradigm that emphasizes fomites and contact transmission, and though the findings may provide insight to broader research understandings, the importance of current prevention techniques such as hand washing should not be overlooked, as they continue to prevent transmission of other common non-airborne diseases such as acute gastroenteritis. The manuscript discusses some limitations however, the manuscript had no exclusion criteria, with the sole inclusion criterion that the children were expected to stay in the same daycare center for the two-year duration of the study. The manuscript can benefit from further exploration of exclusion criteria, as some children are only in daycare for half-days and only 2-3 times a week, thus limiting exposure in the day care setting. This may skew findings particularly with a small N value of 51 subjects in the final analysis. Additionally, using questionnaires from parents may not be objective enough as an indicator of illness, as symptoms of allergies and cold symptoms often have similar presentation particularly at the beginning of illness. Furthermore, the manuscript does not clearly present recommendable actions that result from the findings. The study utilized 45 PACs alongside existing ventilation systems, and the issue of practicality and accessibility to most daycares should be considered. Overall, this study is interesting and demonstrates the potential value of exploring better control of common airborne illnesses in day care centers with additional use of air clearing devices.

Competing interests

The author declares that they have no competing interests.