Maximum Distance of Influenza Droplet Transmission
Influenza droplets travel approximately 6 feet (≤2 meters) through the air, which is the established distance requiring close contact for transmission. 1
Primary Transmission Distance
The CDC and multiple guideline bodies consistently define influenza as spreading through large-particle respiratory droplets that travel only short distances of approximately ≤6 feet through the air. 1 This distance is specifically cited as the threshold for "close contact" transmission when an infected person coughs or sneezes near a susceptible individual. 1
The American Journal of Transplantation guidelines similarly specify that droplets can be directly deposited on mucosal surfaces of people within 3 to 6 feet of the infected patient. 1
Transmission Mechanism and Distance Limitations
Large droplets (≥5 μm) remain suspended for limited time and do not disperse beyond 1.5-2 meters from the source. 1
The droplet size predominantly dictates evaporation and movement after expulsion, with droplets between 60-100 μm being the largest that would totally evaporate before falling 2 meters away. 2
Airborne transmission over longer distances (e.g., from one patient room to another) has not been documented and is not thought to occur with influenza. 1
Important Caveats
Aerosol generation during specific procedures can extend transmission risk. While standard droplet transmission is limited to ≤6 feet, aerosol-generating procedures (such as noninvasive ventilation) have been implicated as possible sources of nosocomial transmission to patients beyond typical droplet range. 1
Small-particle aerosols (<5 μm) may contribute to transmission in the immediate vicinity of the infectious person, though the relative contribution of this mode versus large droplets remains unclear. 1 Research suggests aerosol transmission may account for approximately half of transmission events in household settings. 3
Practical Infection Control Implications
Maintain at least 6 feet separation between potentially infected individuals and susceptible persons in healthcare and community settings. 4, 5
Droplet precautions with surgical masks are appropriate for standard influenza care, as transmission beyond 6 feet through typical respiratory activities is not expected. 1
Surface contamination extends the transmission zone beyond direct droplet range, as influenza virus remains viable on hard surfaces for 24-48 hours and on porous materials for 8-12 hours. 1