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 their building environment. Not only that but is it available at a rate that home owners can afford. One key component of indoor air quality that can have a positive impact on viral transmission and disease severity is the Relative Humidity (RH expressed as a percentage) of the air. In other words how damp the air is.
Maintaining a relative humidity (RH) between 30-60% has been shown to influence the survivability of viruses and therefore reduce the transmission and infectiousness of viral diseases.
Sterling et al. (1985) , synthesised the knowledge at the time into a commonly shared graph of microbial and environmental contaminants on humans at different RH.
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.
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.
Can a Refrigerant Dehumidifier be used Instead of Desiccant?
- A standard refrigeration dehumidifier could indeed be used to maintain a certain humidity level. The issue with that older technology is that water is discharged and indeed water is present always in the interior of that type of dehumidifier. Therefore, the inside of a dehumidifier is humid and the pbe a perfect place for bacteria to breed.
- Hoses that discharge water can also carrier that bacteria away from any infected area.
- The substrate of Ecor Pro desiccant dehumidifier is heated continuously at high heat to kill bacteria and viruses during the during process.
RH and Viral Transmission
- Maintaining an indoor relative humidity between 40%-60% may help to limit the spread and survival of novel coronavirus.
- High temperature, high ultraviolet index, low wind speed, and low relative humidity are contributors to increased MERS-CoV cases (Altamimi et al., 2019) so heating to keep a premises dry is a poor option. The ability to dry without heat is key.
- Cold and dry conditions favour influenza transmission in guinea pigs (Lowen et al., 2007) so it is not advised just to open windows in the winter to let the heat outside.
- Maintaining RH in offices, workplaces and even the home, potentially lessens the 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)
- It should be noted that Compressor (often referred to as Refrigeration) dehumidifiers can typically reach humidity levels down to 45% Relative Humidity (RH) in real terms often 55% RH. DryFan desiccant dehumidifier technology can reach down much lower and often 35% RH in correctly sealed homes if needed so are much more capable of maintaining the correct level of humidity needed to fight viruses.
References & Further Reading
- 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.
- 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
- 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
- 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
- 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