Scientists have known for several months the new coronavirus can become suspended in microdroplets expelled by patients when they speak and breathe, but until now there was no proof that these tiny particles are infectious.

A new study by scientists at the University of Nebraska that was uploaded to a medical preprint site this week has shown for the first time that SARS-CoV-2 taken from microdroplets, defined as under five microns, can replicate in lab conditions.

This boosts the hypothesis that normal speaking and breathing, not just coughing and sneezing, are responsible for spreading COVID-19 -- and that infectious doses of the virus can travel distances far greater than the six feet (two meters) urged by social distancing guidelines.

The results are still considered preliminary and have not yet appeared in a peer-reviewed journal, which would lend more credibility to the methods devised by the scientists.

The scientists took air samples from five rooms of bedridden patients, at a height of about a foot (30 centimeters) over the foot of their beds.

The patients were talking, which produces microdroplets that become suspended in the air for several hours in what is referred to as an "aerosol," and some were coughing.

The team managed to collect microdroplets as small as one micron in diameter.

They then placed these samples into a culture to make them grow, finding that three of the 18 samples tested were able to replicate.

That means, the study says, the virus can spread through the tiny droplets.