Airborne transmission

Airborne transmission or aerosol transmission is transmission of an infectious disease through small particles suspended in the air. Infectious diseases capable of airborne transmission include many of considerable importance both in human and veterinary medicine. The relevant infectious agent may be viruses, bacteria, or fungi, and they may be spread through breathing, talking, coughing, sneezing, raising of dust, spraying of liquids, flushing toilets, or any activities which generate aerosol particles or droplets. This is the transmission of diseases via transmission of an infectious agent, and does not include diseases caused by air pollution. Aerosol transmission has traditionally been considered distinct from transmission by droplets, but this distinction is no longer used. Respiratory droplets were thought to rapidly fall to the ground after emission: but smaller droplets and aerosols also contain live infectious agents, and can remain in the air longer and travel farther. Individuals generate aerosols and droplets across a wide range of sizes and concentrations, and the amount produced varies widely by person and activity. Larger droplets greater than 100 μm usually settle within 2 m. Smaller particles can carry airborne pathogens for extended periods of time. While the concentration of airborne pathogens is greater within 2m, they can travel farther and concentrate in a room. The traditional size cutoff of 5 μm between airborne and respiratory droplets has been discarded, as exhaled particles form a continuum of sizes whose fates depend on environmental conditions in addition to their initial sizes. This error has informed hospital based transmission based precautions for decades. Indoor respiratory secretion transfer data suggest that droplets/aerosols in the 20 μm size range initially travel with the air flow from cough jets and air conditioning like aerosols, but fall out gravitationally at a greater distance as "jet riders".