Viral dispersion in open air

The SARS-CoV-2 pandemic has revived the debate about the routes of virus transmission and their likelihoods. It is of utmost importance to assess the risks of contamination of susceptible people by infectious individuals and to evaluate the level of viral transmission in the community. Most countries have imposed non-pharmaceutical measures to contain SARS-CoV-2 transmission, including social distancing and mask wearing. Here we evaluated the spreading of viruses in open air using harmless Escherichia coli bacteriophages as a surrogate. Phages were sprayed towards Petri dishes seeded with bacteria at different lengths and angles. Median droplets size was 127 {micro}m, similar to those produced by sneeze. Our results showed that the transmission rate decreased exponentially with distance. The highest recorded transmission rate was 9 x 10-6 PFU/plate when phages were sprayed from a 1 m distance, suggesting that the probability of transmission of a single virus at a 1 m distance is 1:100,000. These results agree with the WHO recommendation that face mask protection in an uncrowded well-ventilated space is not required.