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.
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)
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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humidifiers. Please see our full humidifier line here. Neptronic isothermal humidifiers can be an integral part
of mitigation efforts for novel viral outbreaks like COVID-19 as well as seasonal illnesses like influenza.