Evidence Brief: Humidifier use in health care Key messages Improperly maintained cool mist humidifiers can release aerosols containing dissolved minerals and opportunistic pathogens into the air. Therefore, many public health and health care institutions restrict their use. The decision on use of bedside humidifiers for patients should consider the type of humidifier, and cleaning and maintenance of the humidifier. Recommendations by other jurisdictions may also be useful in decision-making. April 2017 Issue and Research Question Humidifiers that atomize water to generate micro-sized droplets in the air (referred to as an Portable bedside humidifiers are used to aerosol) can potentially distribute any microbial increase moisture levels in the air. The use of contaminants present in that water or in humidifiers has benefits and drawbacks. biofilms that develop on humidifier tanks, 1,5 Humidifiers are used to relieve respiratory reservoirs, and spouts. Contaminated room 5 symptoms such as shortness of breath humidifiers can generate high exposures and associated with bronchitis.1 The moisture have been linked to both health care-acquired 6-9 supplied by the humidifier is also used to and community-acquired infections. Given alleviate dry skin2 and help cold sufferers feel the reported benefits versus the potential for better by reducing dryness and irritation to the respiratory disorders, the appropriateness of nose and throat.3 Using humidifiers to keep the allowing bedside humidifiers for patients and relative humidity in the comfort range of 40%– residents in institutions has been a topic of 60% has been shown to decrease survival of debate. The following evidence brief was influenza viruses.4 A humidity level above 60% prepared to inform decisions on whether to should be avoided because it can promote the allow bedside humidifiers for patients. growth of microorganisms, including mould. Evidence Brief: Humidifiers in health care 1 (English) and date of publication (1980–present) Types of bedside humidifiers were applied to the searches. To complement Ultrasonic humidifiers: These this review, references of included papers were produce a micro-sized aerosol when checked for other relevant papers. a reservoir of water is vibrated at Main Findings ultrasonic frequency. Findings from the literature are summarized Impeller humidifiers: A motor- below: driven impeller (spinning disc) draws up water and forces it through a Because several opportunistic pathogens screen, breaking up the water into a (such as Legionella, Pseudomonas, micro-sized aerosol. nontuberculous mycobacteria and Acinetobacter) are found in the natural Evaporative: These use a reservoir environment, they can be introduced into a of water from which a wick filter building’s plumbing system via the public draws moisture A fan blows air over water supply.10 Given the right conditions, the filter, creating moisture (via these opportunistic pathogens can then evaporation of water) and blows the colonize components of the building’s water 10 moisture into the air. supply and contaminate the potable water. If the building tap water is then used in an Steam humidifiers: These boil water aerosol producing humidifier (ultrasonic or to emit water vapour (steam) into impeller unit), the pathogens can potentially the air. However, it is generally be aerosolized into indoor air and pose a cooled to prevent scalding due to health risk. This is particularly true if the the high temperature of the steam humidifier is not routinely cleaned and (>100°C). disinfected and the water in the humidifier’s reservoir is allowed to stagnate. Because ultrasonic, impeller and evaporative humidifiers do not heat Improperly maintained humidifiers have the water, they are commonly been associated with increased risk of illness 1,3 referred to as “cool mist” such as humidifier fever and Legionnaires’ 8 humidifiers by the manufacturers. disease . There are a number of different humidifier Methods designs (see callout box above), each with different levels of risk. Steam humidifiers A review of the literature was executed using (where water is boiled to create water OVID Medline, Academic Search Premier, vapour that is released into the airstream) Environment Complete and Scopus databases, represent a low level of risk of exposure to Google, and Google Scholar. Search terms pathogens, because steam is unlikely to related to humidifiers, cleaning, disinfectant, produce aerosols containing viable and biocide were combined in the search microorganism.11 Similarly, evaporative queries. Limits on the language of publication humidifiers do not pose a significant health Evidence Brief: Humidifiers in health care 2 risk, as they do not generate aerosols. the use of tap water for an ultrasonic Alternatively, because ultrasonic and humidifier) resulted in an outbreak of impeller humidifiers can produce aerosols Legionnaires’ disease in a hospital nursery.15 possibly contaminated with pathogenic bacteria, the risk potential for disease Depending on the geological location, tap transmission is higher, especially in water can be “hard.” Hard water contains a situations where there is a vulnerable person higher concentration of minerals such as 25 in close proximity11,12 The size of the sodium, calcium and magnesium. These particles generated by ultrasonic and mineral particles can be aerosolized (as a impeller humidifiers is small enough to be “white dust”), potentially causing adverse 25 inhaled into the lungs. Highsmith et al. noted reactions in susceptible people. To avoid that fine particles (< 2.5-µm in diameter) this, manufacturers of ultrasonic and constitute >90% but only 60-75% of the impeller humidifiers and researchers often particles generated by ultrasonic and recommend the use of distilled water (or 13,25 impeller humidifiers respectively 13 demineralized water). Some ultrasonic and impeller humidifiers can be equipped A review of the literature indicates that most with demineralizing filters, but these are disease transmission associated with expensive and have to be changed portable humidifiers is due to aerosol frequently. Steam vaporizer and evaporative producing humidifiers, i.e., ultrasonic and humidifiers are not expected to aerosolize impeller units that were not properly any minerals particles into the air. maintained, cleaned or disinfected.6,7,14-19 Fatal lung disease has been reported when Once they become contaminated, bedside ultrasonic humidifiers were run with biocide humidifiers are very difficult to clean. They detergents in the water reservoir rather than can still be a source of exposure even if it being used to clean the reservoir.26-28 cleaning is attempted and they are refilled with sterile water.20 This is especially true if Recommendations for bedside mineral deposits or biofilm are present in humidifiers in health care the humidifier. Mineral deposits and biofilm institutions not only protect the microbes from Various health care institutions and public disinfection, but provide a source of health agencies have made different nutrients for them to proliferate.21 recommendations concerning the use of When it comes to the use and care of home- bedside humidifiers: use humidifiers, guidelines from government Current American National Standards agencies responsible for protecting the Institute/American Society of Heating, general public suggest following the Refrigerating, and Air-Conditioning manufacturer’s instructions.22-24 However, Engineers/American Society for Healthcare different manufacturers have different Engineering (ANSI/ASHRAE/ASHE) requirements, and there has been at least ventilation guidelines state that humidifiers one case where following the should be located within air handling units manufacturer’s instructions (which allowed Evidence Brief: Humidifiers in health care 3 or ductwork, and that steam humidification The National Institutes of Health recently should be used.29 conducted a study to determine the risk to health of their humidifier policy.37 The policy The United States Department of Veterans allows patients to request bedside Affairs, Veterans Health Administration humidifiers, but states that humidifiers requires that only steam be used for building “must be filled with sterile water and that humidification purposes, and prohibits the the humidifier must be discarded after three 30 use of ultrasonic (cool mist) humidifiers. days of use.” In the study, ultrasonic Current CDC environmental infection control humidifiers were filled with sterile water and guidance states that “Reservoir-type the microbial content examined over five humidifiers are not allowed in health care days. The study found that contamination facilities as per AIA (American Institute of appeared after just one day, and increased Architects) guidelines and many state codes. over time. It concluded that aerosolization of Cool mist humidifiers (ultrasonic and potential pathogens by this type of impeller) should be avoided because they humidifier may pose a risk, especially to can disseminate aerosols containing individuals whose immune systems are allergens and microorganisms. Additionally, suppressed. Based on the study’s findings, the small, personal-use versions of this the authors recommended against the use of 37 equipment can be difficult to clean”.31,32 bedside in hospitals. In its guideline for preventing health-care Discussion and conclusions associated pneumonia, the CDC warns Humidifiers are used to help maintain against the use of room-air