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Institute of Medicine (US) Forum on Microbial Threats; Knobler S, Mahmoud A, Lemon S, et al., editors. Learning from SARS: Preparing for the Next Disease Outbreak: Workshop Summary. Washington (DC): National Academies Press (US); 2004.

Cover of Learning from SARS

Learning from SARS: Preparing for the Next Disease Outbreak: Workshop Summary.

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SARS: CLEARING THE AIR

, Pharm. D., , Ph.D., , and .

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The integrated technologies incorporated into the FailSafe Mobile Containment Systems have a wide range of applications, including homeland security, bioterrorism, disaster management, airborne infection control, sick-building syndrome, and facility environmental service applications. The specific objective of this overview is to focus on the use of FailSafe Mobile Containment Systems for isolation precautions in a medical environment. FailSafe has not used these devices directly in an outbreak of severe acute respiratory syndrome (SARS), and thus actual clinical experience will not be reported here. Given that a major component of the spread of SARS occurs via aerosolized droplets, the systems described for clearing the air may be applicable to the containment of this new viral pathogen in hospitals and health care systems.

The guidelines for isolation precautions for hospitals and health care facilities are outlined by the Centers for Disease Control and Prevention (2004) and American Institute of Architechts (2001). These guidelines outline the precautions that infection control personnel should take to mitigate the spread of infection within facilities and protect the health care worker. Precautions must be taken to prevent the spread of infection from direct contact with contaminated surfaces (contact contamination), from large droplets of infectious material that fall out of the air, or from small droplets that can be carried by the air stream throughout the hospital (airborne contamination).

The guidelines for the creation of an isolation room are based on the principle that the isolation room is maintained under negative pressure to minimize the ability of any airborne contamination from entering the hospital. To validate the design recommendations, the precautions listed in Box 4-1 must be taken.

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BOX 4-1

Considerations for Effective Isolation Rooms.

Failsafe Air Safety Systems Approach

FailSafe Air Safety Systems (FASS) manufactures two medical isolation units the Model 77 and the Model 07 (see Figure 4-6)—that provide personalized isolation and infection control. These medical units employ a patented air safety process that was developed in response to the lack of market availability of portable containment systems. Both the Transport Isolation Unit and the Portable Isolation Unit are equivalent in technology to an isolation room, but have the ability to bring isolation to an infected patient.

FIGURE 4-6. The Model 07.

FIGURE 4-6

The Model 07.

The Model 77 can be moved to an area and set up in minutes. The main components are a prefilter; an industrial, high-capacity, micro-fiberglass HEPA filter; ultraviolet lamp(s); and a high-volume blower.

The Model 07 provides isolation on wheels. At 27 inches wide, a single attendant can handle and move the unit throughout hallways and corridors. The main components are a prefilter; an industrial, high-capacity, micro-fiberglass HEPA filter; ultraviolet lamp(s); and a high-volume blower. These units are also battery powered to provide for isolation during transport.

Both of the Medical Isolation Units can be rolled to the location of a suspected infected patient, where aerosols containing SARS viruses are drawn into the system while clean air is filtered and recirculated into the air. The flexibility of the FASS Medical Isolation Units allows for a wide variety of applications:

  • Immediate isolation of patients with SARS, tuberculosis, or unknown respiratory infection.
  • Coverage during bronchoscopy or other aerosol-generating procedures.
  • Removal of toxic smoke or fumes.

The FASS Medical Isolation Units offer the following benefits:

  • Minimal set-up time to respond immediately to an emergency situation.
  • Dual-use flexibility to provide isolation containment (negative pressure enclosure) at any place at any time.
  • A system that does not alter the infrastructure within the enclosed protective area.
  • A cost-effective solution to emergency isolation.
  • Clean air for extended use.

FASS Applications

The FASS Medical Isolation Units are fume hoods on wheels that combine the proven HEPA filter capacity of 99.97 percent capture at 0.1 microns with ultraviolet light. This toxic microbial capture and containment system builds on years of proven studies specifically involving Bacillus anthracis (anthrax) and smallpox, and can readily be applied to infection control of SARS-related incidents. These units are approved by the Food and Drug Administration (FDA) and satisfy CDC guidelines for isolation. They are the only FDA-approved portable isolation units currently on the market.

SARS Response: Deployment Considerations

FailSafe Medical Isolation Units can be deployed in several ways as a response to a suspected SARS incident:

  1. Immediate isolation and evacuation of a suspected SARS patient.
  2. Transport of infected patients through crowded population (e.g., airports, train stations).
  3. Transport to hospital or triage area.
  4. Transport within hospital (from emergency room to SARS isolation floor).

Emergency workers can provide isolation and unrelated medical treatment to suspected SARS patients within the confines of the Medical Isolation Units while protecting caregivers and the healthy population. Bedridden patients showing symptoms of SARS can be quarantined immediately without having to be moved to another room or facility.

System Description

Both of these FASS Isolation Units combine HEPA filtration with UVGI irradiation. The units consist of a mobile platform that allows the patient to sit in a mobile chair or a bed that is surrounded by a plastic curtain. The outside air is drawn under the curtain, across the patient, and then up into the air-purifying system that consists of a HEPA filter and a UVGI lamp, thereby reducing infectious aerosols such as tuberculosis and SARS.

The FailSafe Mobile Containment System is a patented process (U.S. Patent No. 6,162,118 [18 December 2000] entitled “Portable Isolation Device and Method”) that integrates the technologies of filtration, ultraviolet germicidal irradiation, and ozone oxidation. The FailSafe process primary technology is based on high-efficiency filtration using a glass fiber HEPA filtration media that collects and traps particles greater than 0.1 micron with an efficiency greater than 99.97 percent. The filtration will collect most biological pathogens, including fungi, bacteria, and encapsulated viruses. To ensure that the pathogens collected and trapped on the HEPA filter are neutralized, the HEPA filter media surface face is illuminated with ultraviolet germicidal irradiation. Another advantage of illuminating both faces of the HEPA filter is that viruses smaller than 0.1 micron will be neutralized by irradiation.

FailSafe Mobile Containment Systems (NOT the medical Model 77 or 07 units) also incorporate ozone generation capability as a third technology. Ozone is generated with the use of ultraviolet (UV) lamps that will convert atmospheric oxygen into ozone. At concentrations below NIOSH limits, the ozone will chemically react with volatile organic compounds or odor. The FailSafe Mobile Containment Systems also have the capability of generating very high ozone levels that can be used for neutralizing pathogens on surfaces such as walls, ceilings, and floors.

Setup and Operation

The Medical Isolation Units for health care are designed with operational simplicity to make it a “turnkey” operation and to allow health providers to focus on the individual patient and the biological contamination itself. The units are designed for easy use with three switches, and the controls are simple, as follows:

  1. Power up the system. Check to see that the system is working properly and that the operation light is on. Turn the FASS system ON and select the appropriate fan speed to begin air scrubbing, treatment, and capture.
  2. Identify suspected infected patient.
  3. Place patient in Model 07 chair, or encompass sickbed under Model 77 unit. Place plastic curtains around patient.

Preliminary Efficacy Testing

Laboratory testing: FDA 510k application. The HEPA filtration and UVGI irradiation components used in the FASS units are incorporated in Model 07 and Model 77 to protect medical personnel transporting TB and other infectious patients. Preliminary laboratory testing was performed on these units by an independent laboratory for FDA Class II certification.

Discussion of Biological Efficacy

Filtration

HEPA filters. The safety and health protection offered by HEPA (High- Efficiency Particulate Air) filtered fume hoods has long been established by the FDA, CDC, Environmental Protection Agency (EPA), NIOSH, ASTM, and JCAHO. HEPA Filtration is the “Best Available Control Technology” at 99.99 percent at 0.3-micron efficiency level and is “Generally Accepted Control Technology” at 99.97 percent at 0.1-micron efficiency level. The added feature of the new 0.1-micron advanced filters is the “gel” seal and micro fiberglass construction that allows combining these filters with UV light disinfection. HEPA filters combined with charcoal and prefilters are the highest approved filters available for NIOSH-certified respirators. There are no adverse safety, health, or environmental aspects to HEPA filters. HEPA filters are now the primary filtration media for electronic clean room assembly, hospital surgery rooms, bioengineering, pharmaceutical processes, and any applications where maximum reduction or removal of submicron particulates is required. Air from HEPA filters is free of 99.99 percent of all particles larger than 0.3 microns (including bacterial, fungal, and other opportunistic microbiological organisms) according to the size exclusion as described in Table 4-5.

TABLE 4-5. Relative Size of Fungus, Bacteria, and Viruses.

TABLE 4-5

Relative Size of Fungus, Bacteria, and Viruses.

Generally, HEPA filters belong to the “interception” family of filters and are variously referred to as “absolute” or “super interception.” Such filters have a deep bed of randomly positioned fibers in which the total bed depth is very large in comparison to the average fiber diameter and effective pore or free-path crosssectional area. Even though the media may be only 1/16 thick, this is an enormous distance compared to the 0.3- to 1.0-micron fiber diameter. The passage through which air must flow is not straight, but full of twists and turns. As particulates impact on the fibers, they adhere. Thus the pore size becomes increasingly smaller, resulting in the filter efficacy increasing. New HEPA filters, used by FailSafe in Models 77 and 07, provide efficiency down to 0.1-micron particles at a removal efficiency of 99.97 percent.

HEPA filter bed media manufactured from glass fibers are reflective to ultraviolet irradiation, allowing the UVGI irradiation to partially penetrate the filter bed. The result of the combination of UVGI with ozone generation and the HEPA filter is that the bacteria, fungi, and viruses that are trapped in the filter media will be exposed to sufficient irradiation and ozone concentration to disinfect the filter. The advantage of this antimicrobial treatment combination is that the air stream is inhibited from becoming recontaminated from any growth on the filter media resulting in particle breakthrough.

Ultraviolet

UV irradiation can cause eye damage and surface burns on unshielded human skin, eyes, and other organs. Therefore the UV lights used in the FASS units are sealed inside and not visible to the operator or other personnel.

Ultraviolet radiation, in the wavelength range of 2,250 to 3,020 angstroms as used for air/surface disinfection and sterilization, is referred to as ultraviolet germicidal irradiation or UVGI. Ultraviolet germicidal radiation was first applied to disinfect water systems in 1909. Its use in air purification was first evaluated in the laboratory in the 1920s, in an operating room in the 1930s to sterilize the air in an operating room (Sharp, 1939), and in a school ventilation system to reduce measles infection (Riley, 1972). It is also common practice to use to disinfect medical equipment.

UVGI is currently being employed to control bacteria, fungus, and algae growth on surfaces. European breweries have been using UVGI to control microbial growth on cooling coils since 1975. The use of UVGI can control microbial growth on filter surfaces that are subject to moisture or high humidity that will allow for natural fungal growth. Figure 4-7 illustrates a filter with natural fungal growth and a filter that was irradiated with UVGI at a rated intensity of 100 micro/cm at a distance of 1m from the midpoint of the filter (Kowalski and Bahnfleth, 2000). This surface disinfection protects the air stream from being recontaminated due to bacterial, fungus, or viruses that are collected by the filter media.

FIGURE 4-7. (left) Microbial growth on nonirradiated filters.

FIGURE 4-7

(left) Microbial growth on nonirradiated filters. (right) Microbe-free UV irradiated filters (Kowalski and Bahnfleth, 2000).

Microbial Response to Ultraviolet Radiation

The FASS system is an integration of room recirculation to rid the air of biological threats and surface disinfection to kill the biothreat that is collected on the HEPA filters. The primary target of UV radiation is the microorganism DNA molecule with the predominant injury of strand breakage and the formation of photo-induced byproducts such as thymine diamers. This damaged DNA cannot be used for cell reproduction or for proper mRNA templates that is required for the formation of all cellular toxic products. Viruses are especially susceptible to UVGI, more so than bacteria, and are also difficult to filter because of their size. However, viruses are more susceptible to ultraviolet radiation at wavelengths slightly above the normal UVGI broadband wavelength of 253.7 nm.

Microorganisms, when exposed to UVGI irradiation, will be killed or decreased in population at a rate according to a first order equation:

S(t)=e-kIt

where k = standard decay-rate constant, cm2/microW-s

I = Intensity of UVGI irradiation, microW/cm2

t = time of exposure (sec)

The rate constant [k] is unique to each microorganism and defines its sensitivity of each microorganism to UVGI intensity.

The dose of ultraviolet radiation that an airborne microbe receives depends on the amount of time the microbe is being irradiated and the UV intensity. The upper limit of kill rate is obtained by mixing the air within the UVGI exposure chamber. This mixed airflow will have an average velocity that will determine the exposure time required for all microbes in the air stream. If the air is not mixed, then the flow will be partial laminar resulting in the microbes receiving different dosages of UV radiation. Microbes nearest the UV lamp will get the highest dosages and those near the wall of the chamber will have significantly less exposure to the UV radiation. Laboratory experiments can be used to determine the upper limit of Kill Rate Constant (mixed air) and lower limit of Kill Rate Constant (unmixed air).

Ozone

Ozone, an allotropic form of oxygen, possesses unique properties when it oxidizes or interacts with chemical and biological systems. Ozone, best known for its protective role in the earth’s ecological environment and its interaction with industrial pollutants, has bactericidal, virucidal, and fungicidal actions that have been used in water treatment, odor control, and medicinal applications. Ozone [O3], a powerful oxidant reacting with organic molecules containing double or triple bonds, yields many complex byproducts. It is this property of ozone that has been applied as a disinfectant and sterilant against bacteria, viruses, and fungi.

Although the inhibitory and lethal effects of ozone on pathogenic organisms have been observed since the latter part of the 19th century, the mechanisms for these actions have not yet been satisfactorily highlighted. The most often cited explanation for ozone’s bactericidal effects centers on disruption of envelope integrity through peroxidation of phospholipids. There is also evidence for interaction with proteins (Mudd et al., 1969). In one study (Ishizaki et al., 1987) exploring the effect of ozone on E. coli, investigators found cell membrane penetration with ozone, subsequent reaction with cytoplasmic substances, and conversion of the closed circular plasmid DNA to open circular DNA. It is notable that higher organisms have enzymatic mechanisms to stabilize disrupted DNA and RNA, which could provide a partial explanation for why, in clinical treatment, ozone appears to be toxic to infecting organisms and not to the patient (Cech, 1986).

Ozone possesses fungicidal effects, although the mechanism is poorly understood. In one study, Candida utilis cell growth inhibition with ozone was greatly dependent on phases of their growth, budding cells exhibiting the most sensitivity to its presence (Matus et al., 1981). Interestingly, low doses of ozone stimulated the growth and development of Monilia fructagen and Phytophtora infestans, while higher doses were inhibitory (Matus et al., 1982). Thus, high concentrations of ozone are required for effective antimicrobial activity.

Viruses have been studied during their interaction with ozone (Roy et al., 1981). After 30 seconds of exposure to ozone, 99 percent of the viruses were inactivated and demonstrated damage to their envelope proteins, which could result in failure of attachment to normal cells and breakage of the single-stranded RNA.

The Occupational Safety and Health Administration (OSHA) has set Public Health Air Standards of 0.1 ppm for 8 hours or 0.3 ppm for 15 minutes as the limit of the amount of ozone to which people can be safely exposed. Air cleaners based on ozone must not generate ozone levels above the Public Health Standards, which are far below any antimicrobial activity or effective odor control. Low ozone concentrations, below the EPA-acceptable indoor limit, have been used as air cleaners, but their effectiveness has been questioned by many studies (Dyas et al., 1983; Foard et al., 1997). At high ozone concentration, ozone has been used to decontaminate unoccupied spaces of some chemical and biological contaminants and odors such as smoke.

Air Flow

The Center for Disease Control and Prevention’s guidelines for air flow into an isolation room state that there shall be greater than 12 air changes per hour (ACH). However, a higher ACH means more efficiency in removing any airborne infectious materials. There are two settings on the air flow volumes. The number of ACH obtained is a function of room volume, as illustrated in Table 4-6, which is color coded based on obtaining 12 ACH as the minimal level required for meeting CDC guidelines for isolation precautions.

TABLE 4-6. ACH as a Function of Isolation Room Volume and FASS Capabilities (calculated on a 10 percent reduction in air flow capability).

TABLE 4-6

ACH as a Function of Isolation Room Volume and FASS Capabilities (calculated on a 10 percent reduction in air flow capability).

Summary

The described FASS Medical Isolation Units are available in the United States, Canada, and Asia from FailSafe Air Safety Systems Corporation of Tonawanda, NY. They may offer the best opportunity to increase the numbers of isolation rooms in hospitals and especially in emergency rooms. By doing this, they provide a cost-effective solution to the challenge of new viral pathogen outbreaks. It must be emphasized that these units will only control respiratory transmissions, and are not a substitute for contact precautions or for treatment of the infection itself. Traditional measures still must be instituted to deal with surface contamination. For cleanup of biological contamination, the FASS Mobile Containment Systems also generate ozone to eradicate pathogens from surfaces. These units should be used in conjunction with the Models 77 and 07 for additional remediation of the hospital or emergency room environment.

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It should be noted that the author serves as a paid consultant to the FailSafe Air Safety Systems Corporation and has been involved in the development of these technologies.

Copyright © 2004, National Academy of Sciences.
Bookshelf ID: NBK92445

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