Hospital associated infections (HAI) kill more than 72,000 people in the United States every year. This astounding death rate is greater than the annual combined deaths from AIDS and auto accidents. During 2018, Congress indicated its concern regarding the overall threat of infectious diseases by appropriating $168 million of new investments for the Centers for Disease Control and Prevention.
What is equally astounding is that HAIs can be mitigated through relatively low cost and readily available technologies. These same technologies are also capable of helping slow the rising death rate from antibiotic-resistant microbes (ARMs), which the World Health Organization has characterized as a global concern.
Since the 1930s, many hospitals have relied upon Ultraviolet-C (UV-C) energy to control airborne infectious diseases, but use waned with the arrival and proliferation of antibiotics. In the 1990s, demand for the technology returned following a resurgence of drug resistant infectious microorganisms, which required additional infection control measures (Reed 2010).
Ultraviolet light in the 254-nm wavelength “C” band (UV-C), is particularly effective at killing microbes as it breaks the bacteria or virus DNA chain, rendering the cell incapable of reproducing. Applying UV-C lamps for such a purpose is often called ultraviolet germicidal irradiation (UVGI) and typically includes:
· Disinfecting the air in the upper region of individual rooms (ER waiting rooms, cafeterias, surgical suites, patient rooms, etc.)
· Surface disinfection in hospital patient rooms
· Sterilizing medical equipment
· Disinfecting ventilation air streams in HVAC systems
· Cleaning and keeping clean the surfaces of air-handler cooling coils and drain pans
This article advises that UV-C technologies stand ready to contribute to facility-wide strategies for reducing HAIs and ARMs without adding to their resistance to medicinal treatments.
According to the CDC: “On any given day, about one in 31 hospital patients has at least one healthcare-associated infection.” Hospital acquired infections, also called nosocomial infections, are transmitted by a variety of vectors, including person-to-person, through injection/insertion of medical devices, airborne contact of open wounds, and by respiration of airborne particles.
While this article focuses on airborne pathogens, recent research complicates our understanding of transmission vectors and engineering appropriate preventive measures. For example,
C. difficile, which is picked up from surfaces and person-to-person contact, is responsible for 500,000 infections each year and is linked to at least 15,000 American deaths each year according to a 2015 CDC study. (USDHHS, CDC 2015). Recent studies have shown that while understood primarily as a contact pathogen, C. difficile can be transmitted as an airborne infectious agent (King et. al., 2012; Roberts et. al. 2008; Best et. al 2010). While C. difficile infections can happen anywhere, most deaths from antimicrobial resistant forms are from hospital associated infections (USDHHS, CDC 2013).
HAI rates have long been a concern to hospitals, and some gains are being made in reducing them (CDC 2017). However, new threats emerge, and old ones reemerge almost every year, such as Severe Acute Respiratory Syndrome (SARS), Middle East Respiratory Syndrome (MERS) and more recently the reemergence of Measles. Emerging diseases require time and resources to develop protocols for diagnosing, isolating and treating associated illnesses. During these developmental phases, healthcare workers are particularly vulnerable to emerging diseases, as was the case in Saudi Arabia and the United States with respect to MERS (CDC PR 2014). Note: Although the means of MERS transmission is not known, current protocols require standard, contact, and airborne isolation precautions (CDC Web 2014).
The current scare over the Measles virus, one of the most contagious diseases known to man, is another good case-in-point. Nearly a century ago, Harvard University sanitary engineer, William F. Wells, documented that UV-C killed airborne microorganisms, including Measles. Wells installed UV-C fixtures in several suburban Philadelphia day schools to combat a measles outbreak. He discovered that children in schools with the germicidal technology experienced a 13.3 percent infection rate, compared to 53.6 percent in schools without these fixtures (Perkins et al.,1946).
In other words, vaccines and antibiotics are not the only epidemiological tools available. UV-C as an engineering control can assist in supplementing existing infection-control protocols with another “fortification” layer of protection. Again, UV-C is effective against all pathogens from either emerging or known diseases, and it does not contribute to drug resistance or secondary contamination.
Airborne antibiotic-resistance microbes (ARMs)
The CDC estimates that in the United States, more than two million people are sickened every year with antibiotic-resistant infections, with at least 23,000 dying as a result (USDHHS, CDC 2013). The most dangerous are those that have the potential to spread by the airborne route (Kowalski 2006). Many of these pathogens are now called “superbugs” since they are virtually invincible to standard drug treatments.
ARMs are worth mentioning in the context of UVGI because UVGI is a mechanical means for destroying microbes. UVGI disrupts microbe DNA sequencing at the cellular level, which causes cell death. Microbes cannot build resistance to UVGI.
The World Health Organization, U.S. Dept. of Health and Human Services and Centers for Disease Control are united in their classification of ARMS as a global concern (USDHHS, CDC 2013; WHO 2014). The WHO states that “resistance to common bacteria has reached alarming levels in many parts of the world and that in some settings, few, if any, of the available treatment options, remain effective for common infections.” The CDC report states, “Antimicrobial resistance is one of our most serious health threats. Infections from resistant bacteria are now too common…”
ARM infections are on the rise, threatening not only patients, but healthcare professionals and facility staff, as well. Support for the claim that the rate of airborne transmission of infections is also growing (Fletcher et al. 2004). Evidence exists for airborne nosocomial transmissions of Acinetobacter, Pseudomonas, and MRSA (Allen and Green 1987, Ryan et al 2003 and Farrington et al. 1990). Airborne transmission is a significant threat because it can cause infections to spread rapidly and extensively through a non-immune population (Weinstein 2004). Therefore, source and pathway management should involve airborne transmission and, consequently, enhanced methods of control even though the primary route is considered to be direct contact.
Much attention is focused today on pathogenic microorganisms that have developed resistance to antibiotic treatment, or entire types or classes of antibiotics. The loss of effective antibiotic treatment undermines the ability of healthcare to fight infectious diseases and manage the infectious complications common among immunocompromised patients (USHHS, CDC 2013).
Ultraviolet germicidal irradiation
UVGI helps combat ARMs and, more generally, HAIs, by decreasing their concentration in facilities. For all ARMs classified by the CDC and U.S. Dept. of Health and Human Services, the first of a four-part strategy for combating them is “Preventing infections from occurring and preventing resistant bacteria from spreading.” UVGI is particularly effective for addressing this strategy.
How UVGI systems work and how they are addressed through lifecycle considerations of design, installation, commissioning, operations, and maintenance has been described in a number of technical articles published by engineering magazines.
For all its strengths, UVGI is not a stand-alone means to combat airborne HAIs and ARMs. UVGI systems are supplemental to air filtration, air-pressure control and basic procedures for controlling particulate matter during construction and renovation activities (Memarzadeh, et. al. 2010).
UVGI is listed as a supplemental strategy for airborne infectious agents in several important guidelines, including ASHRAE Standard 170-2017, ANSI/ASHRAE/ASHE 170:Ventilation of Health Care Facilities and the ASHRAE Guideline for Indoor Air Quality, which has been incorporated into the 2018 editions of the Facility Guideline Institute (FGI) Guidelines for Hospitals and Outpatient Facilities.
The primary objective of upper-air UV-C placement is to interrupt the transmission of airborne infectious diseases in patient rooms, waiting rooms, lobbies, stairwells, laundry chutes, and emergency entrances and corridors. All of these spaces can be effectively and affordably treated with UV-C (ASHRAE 2017). Airborne droplets containing infectious agents can remain in a well-ventilated room for as long as six minutes. Upper-air UV-C fixtures can inactivate them in fractions of a second. Operating 24 hours a day, upper-air systems are especially effective at significantly reducing airborne infectious microorganisms and eliminating the potential viability of surface microbes that eventually settle out of room air.
Infections from airborne pathogens are usually spread by people (Nardell and Macher: ACGIH 1999). Upper-air systems control infections at their source by intercepting pathogens in the room where occupants generate them (First et al. 1999). Upper-air systems have been shown to be effective against airborne viruses and bacteria, including chickenpox, measles, mumps, varicella, TB, and viruses that cause colds. In a study by Escombe et al. (2009), guinea pigs were exposed to exhaust air from a TB ward whereby 35 percent of the controls developed TB infections while only 9.5 percent (a 74 percent reduction) developed infections when upper-air UV-C was used.
Measles and influenza viruses and the tuberculosis bacteria are infectious diseases known to be transmitted by means of shared air between infected and susceptible persons. Studies indicate two transmission patterns: (I) within-room exposure such as in a waiting room or patient room; (II) transmissions beyond a room through corridors, and through entrainment within ventilation ductwork where the air is then recirculated throughout the building. Since the 1930s (Wells 1955; Riley and O’Grady 1961) and continuing to the present day (Miller et al. 2002; Xu et al. 2003; First et al. 2007), numerous experimental studies have demonstrated the efficacy of upper-air UV-C for reducing concentrations of infectious agents for all three patterns. Compared to fixtures used in these studies, newer fixtures are available today that provide greater UV-C output and coverage, are less costly, use less power and are less expensive.
Air conditioning systems
A/C systems provide an excellent setting for surfaces that support the growth of bacteria and mold in and around cooling coils, drain pans (Levetin et al. 2001), plenum walls and air filters. Growth of these microbial deposits also leads to coil fouling, leading to an increase in coil-pressure drop and reduction of airflow and heat exchange efficiency (Montgomery and Baker 2006). As performance degrades, so does the quality, amount and pressurization capability of air supplied to conditioned spaces (Kowalski 2006/2009)
Because most hospital codes call for the high-efficiency (HEPA) filters to be located downstream of the cooling coil, the filters can become damp or wet. As such, they should be considered as a potential growth medium and infectious disease reservoir. ASHRAE recommends UV-C lighting to be installed downstream of the cooling coil. If a 360-degree UV-C system is installed as such, it will disinfect both the cooling coil and the filter to eliminate mold and bacteria in and upon both devices. It should be noted that a common coil irradiation installation, using a 360-degree lamp system, will also provide up to a 35 percent kill ratio of tuberculosis in the airstream over and above the air filter’s removal rate (Kowalski 2009).
Although UV-C systems providing ultraviolet germicidal irradiation have been used for nearly 80 years, their application in infection control settings in hospitals has waxed and waned several times. Given the concerning rates of morbidity and mortality of hospital associated infections, and the global concern for antimicrobial resistant microorganisms, healthcare professionals may want to examine currently available UV-C technologies that address airborne infectious agents. In particular, upper-room UV-C systems and UV-C systems that irradiate interior surfaces of air handling units, both of which operate continuously, can greatly reduce concentrations of pathogens in a highly reliable and cost effective fashion.
Daniel Jones is the president of UV Resources, Santa Clarita, Calif.
What is UV-C energy?
UV light comprises a segment of the electromagnetic spectrum between 400 and 100 nm, corresponding to photon energies from 3 to 124 eV. The UV segment has four sections, labeled: UV-A (400 to 315 nm); UV-B (315 to 280 nm); very high energy and destructive UV-C (280 to 200 nm); and vacuum UV.
Most of us are familiar with the harmful effects of UV energy transmitted by sunlight in the UV-A and UV-B wavelengths, giving rise to UV “sunburn” inhibitors, or blocking agents, which are found in glasses and lotions. We are also familiar with products engineered to withstand the effects of UV radiation, such as plastics, paints, and rubbers. However, unlike the UV-A and UV-B wavelengths, the UV-C band has more than twice the electron volt energy (eV) as UV-A, and it is well absorbed (not reflected) by organic substances, adding to its destructiveness.
UV energy’s killing power
UV-C’s germicidal or germ-killing effects are well proven. The UV-C wavelength owes these destructive effects to the biocidal features of ionizing radiation; or, more simply, UV-C does far more damage to molecules in biological systems than temperature alone can. Sunburn, compared to the sensation of warmth, is one example of that damage. Sunburn is caused by sunlight striking and killing living cells in the epidermis; the resulting redness from a sunburn reflects the increased capillary action and blood flow that allow white blood cells to remove the dead cells.
It is this ionization function that drives UV-C’s power to alter chemical bonds. The 254 nm wavelength carries enough energy to excite doubly-bonded molecules into a permanent chemical rearrangement, causing lasting damage to DNA, ultimately killing the cell. Even a very brief exposure to UV-C can permanently eliminate microbial replication
How to apply germicidal technology
There are multiple approaches to using UV-C to ensure the greatest practical control of microbes and airborne microorganisms in communal spaces, including:
Upper-Air Disinfection: The primary objective of upper-air UV-C germicidal fixtures is to interrupt the transmission of airborne infectious diseases in communal spaces (e.g., waiting areas, cafeterias, sports facilities, etc.). Airborne droplets containing infectious agents can remain in room air for 6 minutes and longer. Upper-Air UV-C fixtures can destroy those microbes in a matter of seconds. Kill ratios over 99.9 percent on a first-pass basis have been modeled and, as air is recirculated, concentrations are further reduced by each subsequent pass (“multiple dosing”).
HVAC Surface Cleaning: Surface-cleaning UV-C systems provide 24/7 irradiation of HVAC/R components to destroy bacteria, viruses and mold that settle and proliferate on HVAC coils, air filters, ducts and drain pans. UV-C prevents these areas from becoming microbial reservoirs for pathogen growth that will eventually spread into airstreams. A system installed for surface irradiation, can also provide first-pass kill ratios of airborne pathogens of up to 30 percent, with ancillary benefits of restored cleanliness, heat-exchange efficiency and energy use.
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