Controlling Infections Through Relative Humidity

It’s a generally agreed fact that infections are bad. We go to extraordinary lengths to avoid getting infected, whether it’s a common cold or something much more serious. Out in the world, there might not be too much we can do to prevent it, but in certain environments infection control and prevention is an absolute necessity. Think of a hospital, an operating room, food processingor a pharmaceutical facility. Where a simple infection could not just make one person a little ill, but potentially infect thousands of people, or cause complications and even death for a patient. In these environments, infection control is at the top of the priority list. Over the last few years there has been a growing awareness of the relationship between relative humidity in an environment (otherwise known as RH) and pathogens like bacteria or viruses that can cause infections. But to really understand this, we need to look at the interactions that can happen between pathogens (airborne and surface) and the RH of a room.


Airborne Pathogens And Viruses

One of the most common causes of infection from viruses is the inhalation of contaminated air. For example, speaking, coughing and sneezing can all expel large numbers of ‘aerosols’ (suspensions of solid or liquid particles in the air), which could include viruses and bacteria. The smaller the particles are, the longer they will stay in the air and the further they will travel when expelled. When exposed to dry air, most of the moisture content in the aerosol will evaporate instantly, making the suspended particles smaller and lighter, able to travel further and survive longer. But both temperature and relative humidity affect the airborne survival of viruses, bacteria and fungi. Being able to control these variables and keep the temperature and RH at an optimum level can drastically reduce the survival (and therefore transmission of) all kinds of airborne infections. This will vary depending on the area or the infections most likely to be present. For example, viruses like influenza or norovirus can survive longer at an RH of 20-30%, while keeping the RH between 40-70% will minimise their survival rate. Tests also show that the infectivity of the influenza virus is increased by very low and very high RH, with minimum infectivity at around 50%.  Similar results have been found for airborne pneumococci, streptococci and staphylococci. This is one of the reasons that hospitals and labs in particular need to be able to control the RH in different areas of their environment, to minimise the lifespan of various infections. For example, it’s recommended that operating theatres should maintain an RH of 60%, while newborn baby units and hydrotherapy areas should be kept at 40%.


Surface-Borne Infections

We then move on to the surface-borne infections. When RH is very low, static electricity can be an issue, and raising the RH above 35% allows surfaces to become covered in a thin film of moisture that dissipates the static charge. This thin film of moisture also makes surface cleaning much more effective. Studies have shown that the impact of RH on surface infections and cleansing is high – with the survival of viruses like MRSA (Methicillin Resistant Staphylococcus Aureus) are significantly reduced when contaminated surfaces are kept between 45-55% RH. There are also some bacteria that will form protective spores when the RH drops below 40%, which makes them more resistant to surface disinfectant and more likely to survive. So keeping the RH at appropriate levels will dramatically improve the effectiveness of surface cleaners and reduce the presence of infectious bacteria, viruses and fungi.


Infection Resistance

Maintaining a consistent and appropriate RH also has an impact on patients and workers and their ability to become infected. Studies show that when RH is kept consistently below 40% individuals are more susceptible to infections, mainly due to the fact that the moist tissues in the body (like the nose, throat and lungs) become dried out. So, maintaining mid-range RH levels not only impacts the survival rate of viruses and bacteria, but it also helps boost the body’s natural infection resistance.


Why Will Controlling RH Help?

Overall, controlling the RH of an environment can help significantly reduce the likelihood of infections from viruses, bacteria and fungi on multiple levels. From controlling the lifespan of infectious particles in the air, boosting the body’s ability to resist them and ensuring surfaces can be properly disinfected, RH has much more of an impact than many think. In fact, it’s such a critical thing that there are regulations in place for hospitals, including what the RH should be for certain areas. For example, the Health Technical Memoranda (HTM) Guidelines 7.48 and 7.50 define the acceptable range of humidity as between 35% and 60% saturation. The Scottish Health Facilities Note 30 – “Infection Control in The Built Environment” states that control and physical monitoring of humidity can help ensure that environmental conditions do not contribute to the spread of infection.

In the UK, most of our RH problems tend to be because of low humidity. Particularly during the winter months, buildings are heated to around 20°C, and as the temperature rises the RH falls dramatically. Where comfort air conditioning is used to cool us in the summer months, the cold surfaces within the system also remove moisture, leading to low humidity. This creates the perfect breeding ground for infections, and is why we will often see infections bouncing around air-conditioned offices in summer, and running rampant in winter.

To avoid this, we recommend using a humidifier to introduce moisture back into the air and raise the RH. But how you go about that will depend on the environment you are trying to regulate. For hospitals, Humidity Solutions can design and supply a sophisticated RH control systemto optimise the RH in individual zones, allowing for the complete control of the environmentacross a medical facility, which will minimise the risk of infection. At Humidity Solutions, we provide RH control solutions for hospitals, pharmaceutical labs, offices and much more. Your solutions will be tailored to your needs, so you can be sure your RH and infection are being managed and controlled effectively. For more information on our solutions, or to ask us about infection control in your organisation, just get in touch with the teamat Humidity Solutions today.