Table 1.

Environmental factors associated with survival of airborne infectious agents13, 26, 27, 28, 29, 30

Environmental factor	Viruses	Bacteria	Fungi
Temperature	•As temperature increases, survival decreases •DNA viruses are more stable than RNA viruses at higher temperatures	•Temperatures >24°C decrease survival	•Highest fungal counts occur in the summer, at higher temperatures
RH*	•Enveloped viruses (most respiratory viruses, influenza) survive longer at lower RH (20%-30%) •Nonenveloped viruses (adenovirus, rhinovirus, and polio virus) survive longer in higher RH (70%-90%) •Exceptionally, nonenveloped rotaviruses survive best at medium RH	•Most gram-negative bacteria survive best in high RH and low temperature, except Klebsiella pneumoniae, which is stable at RH 60% •Gram-positive bacteria have the highest death rates at intermediate RH •Sudden changes in RH reduce survival	•Dehydration and rehydration of fungi particles provide conflicting results •Spore concentrations seem higher at higher RH
Atmospheric gases	•Ozone inactivates airborne viruses to a greater degree than bacteria or fungi	•CO decreased survival at low RH (<25%), but protected bacteria at high RH (90%)	•Oxygen supports growth
Light and irradiation	•UV light is harmful (RH-dependent)	•UV light is harmful but may be mitigated by higher RH (water coat protects aerosolized particles)	•More resilient to the effects of UV light than viruses or bacteria
Surrounding organic material (eg, saliva, mucus)	•Protects viruses from environmental changes	•May affect survival based on RH	•Decomposition of organic waste (food remains) may act as a source of fungal spores

CO, carbon monoxide; RH, relative humidity; UV, ultraviolet.

^*RH is a measure of the amount of water vapor in the air at a specific temperature; therefore, temperature and RH always interact to affect survival.