EXP COVID-19 Offices White Paper

PREVENTION | 11

If the more sophisticated FLIR approach is outside your budget, simple thermal skin temperature devices can be used by staff to read temperatures of arriving guests. While the use of EST screening does not eliminate the possibility of admitting an infectious individual past a checkpoint, when combined with other measures of disease transmission mitigation, it is a first step in reducing transmission risk to guests and staff. transmission of viruses and resulting infections. Proper relative humidity (RH) of the air in a space can decrease disease transmission by both maximizing the ability of our lungs to fight the virus as well as shortening how long the virus survives in droplets in the air. Researchers of viral diseases have found very high humidity levels support viral spread as the virus can survive for longer periods of time on the surfaces they may settle down on. Also, very low levels of relative humidity (RH) correlate with higher infection rates. The ideal relative humidity range has been found to be between 40-60%. Studies also show that the viability of viruses in suspended aerosols and droplets is RH dependent. (6) These results suggest that environmental conditions have the potential to influence the transmission of certain pathogens by affecting their viability while they are transmitting between hosts. While bacteria survived better at humid conditions than dry conditions, viruses survived best at both low and extremely high RHs while experiencing greater decay at intermediate RHs. At low humidity, it is easier for airborne viral particles to travel because they shrink and can float longer. As relative humidity increases, the hygroscopic attraction brings particles together to form larger droplets that have a longer float time and can be more easily removed through the HVAC system. The difference in HUMIDITY (12) Indoor humidity appears to play a role in the

Figure 8. Humidity Dependent Decay of Viruses, but Not Bacteria, in Aerosols and Droplets (13)

viability patterns between viruses and bacteria suggests that different mechanisms may dominate the humidity- dependent decay of the two. In addition to decreasing virus transmission, humidity control can support the occupant’s immune system. Mucus membranes and cilia are the body’s first line of defense to help sweep out pathogens from the respiratory systems. Then interferon is released to help slow the spread of the virus. Dendritic cells and macrophages can also help kill viruses. T cells and B cells are then activated to help produce antibodies and kill infected cells. All these defense systems are inhibited at low relative humidity. Low humidity decreases protection, increases inflammation, and slows down tissue repair. There is a lot of data to support these theories. Studies have shown that “Dry air exposure of mice impairs epithelial cell repair in the lung after influenza virus infection.” (14) In Wuhan, China, researchers confirmed that respiratory infection was enhanced during unusually cold and low humidity conditions. In a four-year study monitoring infection rates

Low humidity decreases protection, increases inflammation and slows down tissue repair.

Ideal relative humidity range 40-60%