As discussed in earlier blogs, microorganisms can survive in the environment for long periods of time and it has become clear that eliminating microorganisms from the patient immediate and non-immediate surroundings significantly contributes to the reduction of HAIs. It has also become clear that environmental terminal cleaning and disinfection with germicides is not always efficacious and it has been estimated that 5%-30% of environmental surfaces remain contaminated with nosocomial pathogens (1). Therefore, there is increased interest in using touchless technologies, such as chemical fumigation and ultraviolet germicidal irradiation, which effectively kill microorganisms and can also reach hard-to-access surfaces in healthcare facilities.

There have been a number of chemicals tested for use as fumigants, such as hydrogen peroxide vapor and dry mist, chlorine dioxide, super-oxidized water and ozone. The EPA tests of sporicidal efficacy found significant differences between the fumigants used, the type of surface examined, and the type of microbial spore tested. All fumigants performed better on non-porous materials, while carpets were the most difficult to decontaminate. The most promising no-touch methods use either UV irradiation or hydrogen peroxide fumigation.

Hydrogen peroxide (H2O2) has broad-spectrum efficacy against viruses, bacteria, yeasts, and bacterial spores. Hydrogen peroxide kills microorganisms by generating hydroxyl free radicals that damage the microorganisms’ membrane phospholipids, nucleic acids and other cellular components (2). Hydrogen peroxide vapor systems use 30%-35% H2O2 and require between 1.5 hours to 8 hours of disinfection depending on the specific system. Importantly, hydrogen peroxide breaks down into oxygen and water, leaving no toxic residues.

Ultraviolet (UV) irradiation kills microorganisms mainly by damaging the microorganisms’ nucleic acids, but also by affecting their enzymes, amino acids, and the membrane phospholipids. UV wavelength in the range of 200 to 295 nm is the most effective in breaking cellular DNA, thereby destroying the organism. Indeed most UV room disinfection devices use UV-C irradiation which has a characteristic wavelength of 200-270 nm. The efficacy of UV irradiation devices depends on many parameters, such as the organic load present, dose, exposure time, distance of the microorganisms from the device, the device intensity, lamp placement and direct line between the device and the location of the microorganisms. It has been found that double stranded viruses were more resistant than single DNA viruses, and that bacterial and fungal spores are highly resistant to UV inactivation, and photoreactivation has been demonstrated (3). In general, microbes are better inactivated by the UV irradiation when in the air than when on surfaces; the microorganisms concentration does not significantly influence the killing efficacy of the devices; presence of organic load has a negative impact on the killing efficacy of the devices; and the higher the distance of the device from the microorganisms, the lower their efficacy. Recently efforts have been made to increase UV germicidal efficacy by combining it with photocatalysts like TiO2 or Ag. For example, there are aerosolized hydrogen peroxide systems that combine 5%-7% H2O2 with <50 ppm Ag cations requiring shorter periods of disinfection (2-3 hours).

While hydrogen peroxide and UV irradiation have demonstrated high kill rates, environmental surfaces will be constantly re-contaminated, and the CDC does not recommend chemical fogging for general infection control (4). It should be noted that several recent clinical trials have shown that the use of UV devices and hydrogen peroxide systems resulted in reduction of HAI (to be discussed in the next blog).

Unfortunately, there are significant concerns for the safety of patients and workers that may be inadvertently exposed to hydrogen peroxide or UV irradiation when used in the medical environment. Exposure to hydrogen peroxide may cause neurological, respiratory and other damage, and exposure to UV can cause deleterious effects to the skin, eyes, and immune system. It is also known that all forms of UV can cause skin cancer. Limiting exposure to hydrogen peroxide or UV irradiation must thus be considered in areas where humans or animals may be present. Furthermore, especially regarding fumigation, even neighboring areas may be affected, as the fumigating agents may move through ventilation or sewer lines, as was the case in several unfortunate accidents (reviewed by 5). Using fumigation requires careful sealing of ventilation ducts, plumbing fixtures, doors, windows and any other openings with a material that will resist penetration. Blocking ventilation ducts causing changes in room pressurization or increasing room leakage could contribute to infection spread (6).

References

  1. Weber DJ, Rutala WA, Anderson DJ, Chen LF, Sickbert-Bennett EE, Boyce JM. Effectiveness of ultraviolet devices and hydrogen peroxide systems for terminal room decontamination: Focus on clinical trials. Am J Infect Control 2016;44(5 Suppl):e77-84.
  2. Davies A, Pottage T, Bennett A, Walker J. Gaseous and air decontamination technologies for Clostridium difficile in the healthcare environment. J Hosp Infect 2011;77:199-203.
  3. Quek PH, Hu J. Influence of photoreactivating light intensity and incubation temperature on photoreactivation of Escherichia coli following LP and MP UV disinfection. Journal of Applied Microbiology, Vol. 105, No. 1, 2008, pp. 124-133.
  4. CDC. Guidelines for Environmental Infection Control in Health-Care Facilities: Recommendations of the CDC and the Healthcare Infection Control Practices Advisory Committee (HICPAC). MMWR, Vol. 52 (No. RR-10), No. 2003, pp. 1-48.
  5. Byrns G. Alternative Room Disinfection Modalities – Pros and Cons, In: Use of Biocidal Surfaces for Reduction of Healthcare Acquired Infections. G. Borkow, Ed. pp 187-207.
  6. Byrns G, Fuller TP. The Risks and Benefits of Chemical Fumigation in the Health Care Environment. Journal of Occupational and Environmental Hygiene, Vol. 8, No. 2, 2011, pp. 104-112.