An impactor-based aerosol platform for probing indoor, short-range transmission dynamics: a Phi6 bacteriophage study

1. ABSTRACT Short-range transmission is a driver of airborne disease spread. However, limited knowledge exists on the immediate impact of host, environmental, and seasonal factors on viable pathogen-laden droplets (VPLD) shortly after release. This work modelled the effects of respiratory droplet size, airway mucus composition, viral loads, and seasonal variations in indoor relative humidity (RH) on the number of VPLD collected shortly after equilibration. Clinically relevant concentrations of the SARS-CoV-2 surrogate bacteriophage, Phi6, were prepared in solutions reflecting the solute content of the airway mucus in healthy and disease states. Low solute levels and viral loads, characteristic of the presymptomatic phase, increased VPLD counts (initial diameter range, 5.59 to 20.28 µm) under low indoor RH in temperate winter. Elevated solute levels and decreased viral loads, characteristic of the late symptomatic phase, reduced VPLD counts (initial diameter range, 1.73 to 20.28 µm) under intermediate RH in temperate summers. High viral loads, characteristic of the early symptomatic phase, resulted in comparable VPLD counts (initial diameter range, 1.73 to 20.28 µm) across solute levels and RH, indicating a buffering effect of high viral loads against inactivation. These findings, integrated with complementary lines of evidence, were used to describe potential mechanisms of short-range transmission dynamics. SYNOPSIS This study investigated the effects of four factors including respiratory droplet size, mucus composition, viral load, and seasonal variations in indoor relative humidity, on the recovery of viable pathogen-laden droplets to understand short-range transmission dynamics. Competing Interest Statement The authors have declared no competing interest. Funding Statement CIHR, NSERC, CRC 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I confirm that all necessary patient/participant consent has been obtained and the appropriate institutional forms have been archived, and that any patient/participant/sample identifiers included were not known to anyone (e.g., hospital staff, patients or participants themselves) outside the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 Data Availability All data produced in the present study are available upon reasonable request to the authors