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Humidification is more
than comfort...
It is about public health

Climate Conditions
Climate
Conditions

Altamimi, A., & Ahmed, A. E. (2019). Climate factors and incidence of Middle East respiratory syndrome coronavirus. Journal of Infection and Public Health, In Press. DOI:10.1016/j.jiph.2019.11.011

The Effects of Air Temperature and Humidity
The Effects of Air Temperature and Humidity

Casanova, Lisa M., et al. "Effects of air temperature and relative humidity on coronavirus survival on surfaces." Appl. Environ. Microbiol. 76.9 (2010): 2712-2717. DOI: 10.1128/AEM.02291-09

COVID-19 Outbreak
COVID-19
Outbreak

Dietz, L., Horve, P.F., Coil, D., Fretz, M., Van Den Wymelenberg, K. (2019). Novel Coronavirus (COVID-19) Outbreak: A Review of the Current Literature and Built Environment (BE) Considerations to Reduce Transmission. Preprints 2020, 2020030197.

The transmission of Influenza
The transmission of Influenza

Lowen, A. C., Mubareka, S., Steel, J., & Palese, P. (2007). Influenza virus transmission is dependent on relative humidity and temperature. PLoS Pathog, 3(10), e151

The Impacts of Home Humidification
The Impacts of Home Humidification

Myatt, T. A., Kaufman, M. H., Allen, J. G., MacIntosh, D. L., Fabian, M. P., & McDevitt, J. J. (2010). Modeling the airborne survival of influenza virus in a residential setting: the impacts of home humidification. Environmental Health, 9(1), 55

COVID-19, Humidification and Human Health

On March 11th, 2020 the World Health Organization (WHO) declared COVID-19 a pandemic after global cases surpassed 118,000 in 114 countries and over 4000 deaths have been attributed to the disease.

The COVID-19 disease is caused by a novel coronavirus (SARS-CoV-2). In humans, coronaviruses cause respiratory tract infections that are usually mild, but occasionally lethal. Coronaviruses were responsible for the deadly outbreaks of SARS (Severe acute respiratory syndrome) and MERS (Middle East Respiratory Syndrome).

With the ongoing spread of the novel coronavirus and COVID-19, government entities, the healthcare sector, schools and universities, and private businesses have an opportunity to reduce potential transmission through the built environment. One key component of indoor air quality that can have a positive impact on viral transmission and disease severity is relative humidity.

Maintaining a relative humidity (RH) between 30-60% has been shown to influence the survivorship of viruses and reduce the transmission and infectiousness of viral diseases.

Sterling et al. (1985) (Fig. 1), synthesized the knowledge at the time into a commonly shared graph of microbial and environmental contaminants on humans at different RH.

Figure1

Figure 1: Effect of pathogens, microbes, and environmental contaminants on human beings. From Sterling et al. (1985).

More recent studies have taken aim at the influence of RH on specific families of viruses, like influenza and coronavirus. These studies focus on the observed survival on surfaces and in the air column, and the rates of infection under different environmental conditions. Below we outline key findings from commonly referenced or recent studies. Links to the studies are posted as well.

RH and Viral Transmission

  • Maintaining an indoor relative humidity between 40%-60% may help to limit the spread and survival of novel coronavirus. Humidification maintains hydrated and intact mucosal barriers of human occupants, resulting in an increase resistance against any microbial attack. (Dietz et al., 2020).
  • High temperature, high ultraviolet index, low wind speed, and low relative humidity are contributors to increased MERS-CoV cases (Altamimi et al., 2019)
  • Cold and dry conditions favor influenza transmission in guinea pigs (Lowen et al., 2007)
  • Maintaining RH in offices and workplaces lowers potential risk for transmission of viral diseases (Wolkoff, 2018 and references therein).

RH and Virus Survival

  • While coronaviruses are durable on surfaces relative to influenza viruses, survival rates are reduced at moderate RH of 50%. (Casanova et al., 2010)
  • The infectiousness of airborne influenza viruses was significantly reduced when RH was above 40% (Noti et al., 2013)
Figure1

Figure 2. The percent infectivity of airborne influenza at a constant temperature (20°C, 68°F). Curve shows all size fractions (>4 µm, 1–4 µm, and <1 µm). From Noti et al., 2013.

RH and Recovery

  • Humidification in homes can reduce survival of influenza and promote recovery, by improving restfulness, in sick individuals (Myatt et al., 2010)
  • Maintaining 40-45% RH in hospitals reduced perceived air dryness and airway symptoms of patients and hospital staff (Nordström et al., 1994).

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Air Quality Effects
Air Quality Effects

Nordström, K., Norbäck, D., & Akselsson, R. (1994). Effect of air humidification on the sick building syndrome and perceived indoor air quality in hospitals: a four month longitudinal study. 51(10), 683-688.

Humidity in Occupied Buildings
Indoor Air Humidity, the importance of our health

Wolkoff, P. (2018).
Indoor air humidity,
air quality,and
health–An overview. International journal
of hygiene and
environmental health, 221(3), 376-390.

High Humidity stimulate coughing
High Humidity stimulate coughing

Noti, J. D., Blachere,
F. M., McMillen, C. M., Lindsley, W. G., Kashon,
M. L., Slaughter, D. R., & Beezhold, D. H. (2013).
High humidity leads
to lossof infectious
influenzavirus from
simulatedcoughs. PloS one, 8(2).

Humidity in Occupied Buildings
Humidity in Occupied Buildings

Sterling, E. M., Arundel, A., & Sterling, T. D. (1985). Criteria for human exposure to humidity in occupied buildings. ASHRAE transactions, 91(1), 611-622