Exposure to respiratory fluids -- very fine respiratory droplets and aerosol particles -- present in air and which carry viruses are the main reason for contracting Covid-19 infection, the US Centers for Disease Control and Prevention (CDC) said.

People release respiratory fluids during exhalation -- quiet breathing, speaking, singing, exercise, coughing, sneezing in the form of droplets. While large droplets settle out of the air within seconds to minutes, very fine droplets can remain suspended in the air for minutes to hours. These droplets carry viruses and transmit infection, said the agency`s latest science brief as part of its public guidelines on Covid-19.