Microdroplets generated by speech can remain suspended in the air in an enclosed space for more than ten minutes, a study published Wednesday showed, underscoring their likely role in spreading Covid-19.

Researchers at the National Institute of Diabetes and Digestive and Kidney Diseases (NIDDK) had a person loudly repeat the phrase "Stay healthy" for 25 seconds inside a closed box.

A laser projected into the box illuminated droplets, allowing them to be seen and counted.

They stayed in the air for an average of 12 minutes, the study published in the journal Proceedings of the National Academy of Sciences of the United States of America (PNAS) showed.

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