# Loss of Infectivity of Influenza Virus and SARS-CoV‑2 during Aerosol Sampling

## TL;DR

This study shows that influenza and SARS-CoV-2 viruses lose infectivity quickly during aerosol sampling unless they attach to cells rapidly.

## Contribution

The study introduces a novel method to assess virus infectivity loss during aerosol sampling by comparing deposition onto cells versus liquid.

## Key findings

- Aerosolized IAV and SARS-CoV-2 lost infectivity by approximately 2 log10 PFU within 10 minutes unless attached to cells.
- Depositing aerosols directly onto cells resulted in 100× more plaque forming units compared to liquid medium.
- The discrepancy was not due to uneven aerosol distribution or inefficient virus recovery.

## Abstract

Our understanding
of transmission of influenza virus and other
respiratory viruses is limited by the difficulty of detecting infectious
viruses in aerosol particles. Most aerosol sampling methods are believed
to contribute to virus inactivation, but the magnitude of this sampling
artifact is unknown. To investigate this question, we aerosolized
influenza A virus (IAV) and SARS-CoV-2 suspended in human saliva into
a small chamber (3.7 L). Aerosols settled for 10 min onto either cells
or a thin layer of liquid medium that was immediately transferred
to cells for plaque assay. Aerosols that deposited directly onto cells
led to the formation of 100× more plaque forming units (PFU)
compared to aerosols that deposited first into liquid medium. Further
experiments ruled out uneven aerosol distribution in the chamber or
inefficient virus recovery as causes of this discrepancy. These findings
indicate that aerosolized IAV and SARS-CoV-2 lost infectivity by approximately
2 log10 PFU within ∼10 min unless they attached
to cells quickly. As natural infection via inhalation occurs by direct
deposition of the virus onto cells, we hypothesize that sampling directly
onto cells more accurately reflects the potential for exposure to
lead to infection.