Sir, so far, we are aware of two main routes of transmission SARS-Cov-2: infection by contact with a contaminated object and inhalation of droplets emitted by sneezes and coughs. However, there may be a third infection route of microdroplets, which can remain in the air for perhaps 20 minutes or more, particularly where ventilation is poor. Recent experiments have been undertaken in the Kyoto Institute of Technology and the Japanese Association for Infectious Disease. Laser beams and high sensitivity cameras, which can capture microdroplets 0.01 micrometres in width, have been used to analyse the aftermath of sneezes and coughs. Droplets fall relatively quickly, but small particles (less than 10 micrometres in width) can remain in the air for prolonged periods.

Similar experiments have been undertaken assessing close range conversations where microdroplets can be seen generated during speech, particularly loud conversational speech or heavy breathing (such as after a jog). Stagnation of microdroplets can be minimised with good ventilation and increased air circulation. It is not known what volume of microdroplets can lead to infection, but the possibility that such microdroplets may transmit the virus cannot be ruled out. The risk is that it may be spread by speaking to someone, or potentially being in an area where others have been speaking, particularly if ventilation is poor, and masks are not being worn. Consider the areas in hospitals where most conversations take place, such as offices or corridors, many with inadequate or no ventilation. The implications of this data will become clearer as our understanding improves, but in the meantime, extra caution may be better than the alternative.