Contamination Control In Hospitals (June 2000)
One of the obvious ways to control costs is to defer spending on “low visibility” budget items that seemingly have no direct impact on patients. Such cuts often are directed at the budgets for routine servicing of hvac systems, causing air quality to suffer as a result.
‘Invisible’ ProblemsBecause indoor air quality (IAQ) problems are difficult to quantify and are not always readily apparent, poor IAQ is often not recognized as a problem until a crisis occurs. Although relatively rare, some hospitals do not perform such basic hvac maintenance as changing filters, cleaning ducts, testing air quality, and ensuring that adequate ventilation rates are maintained. Most hospital facilities managers have become much more proactive in the 90s regarding maintenance issues, however. Nevertheless, it is still rare to find a hospital which performs comprehensive, building-wide IAQ testing. Our firm, which investigates problem buildings, is usually contacted when a hospital has a major problem that is publicized or one that results in a lawsuit.
Air quality in many hospitals has deteriorated to a point that airborne transmission of infectious disease has become a significant problem. Given the fact that many infections are transmitted via the airborne route, such as tuberculosis (TB) and Legionnaire’s disease, adequate ventilation becomes more critical than ever. Newly discovered strains of antibiotic-resistant bacteria make infection control one of the top priorities for health care providers. The ever-increasing numbers of orthopedic replacement procedures and organ transplants make air quality in sterile operating rooms, isolation rooms, and general patient rooms a critical issue in patient care.
Occupational exposure to toxic and hazardous gases and particulates are important concerns for health care providers. Nursing staff who routinely administer antibiotics can themselves develop resistant strains of microbes that can hinder treatment if they acquire infections. Health care workers involved in administering chemotherapeutic drugs can be accidentally exposed to toxic levels of the drug. Certain types of lab work can result in exposure to such organic solvents as formaldehyde, xylenes, methylene chloride, toluene, and others. Some of these compounds may be carcinogenic and many are toxic at relatively low exposure levels. Glutaraldehyde exposure from cleaning of brochoscopes can result in toxic exposures at concentrations well below 1 ppm. OSHA has enacted mandatory blood-borne pathogen requirements as the result of concern over exposure during procedures.
The primary method of contracting an infection is skin or mucous membrane contact with contaminated surfaces or instruments. To prevent this means of infection, infection control staff give considerable attention to sterilizing reusable surgical equipment and supplies. Much of the equipment and supplies are disposable, single-use items. As a result, infections spread via this contact are probably at, or near, a minimum at present.
The reduction in viable microorganisms in air is an obvious objective that would reduce nosocomial infections. This is an area that deserves, and is beginning to receive, the attention it demands.
To minimize the risk of airborne infections during orthopedic surgery, practitioners have demanded laminar-flow operating rooms (both horizontal and vertical air flows). Also, many surgeons operate in fully encapsulated suits with HEPA-filtered breathing air and filtered inhaled air. In essence, these operating rooms are “cleanrooms” with efficiencies as low as the Class 10 range. Interestingly, surgeons are increasing their use of encapsulated suits out of concern for their own well being, as well as for their patients’ benefit. The high-speed cutting tools used in orthopedic surgery create significant aerosols from blood and fluids at the wound site. Therefore, any blood-borne pathogens present in these fluids could be inhaled, infecting the operating-room staff.
Strategies to Reduce ContaminationSeveral strategies are available when dealing with airborne infections in hospitals, such as improved maintenance and system cleaning, increased ventilation, “source control,” ultraviolet germicidal irradiation (UVGI), and filtration.
Hvac maintenance cleaning, often inaccurately described as “duct cleaning,” appears to have considerable value in reducing airborne microorganism concentrations. Studies are extremely limited (we are unaware of any studies dealing with the impact of duct cleaning in hospital settings), but suggest that viable microorganism concentrations may be reduced 80% to 90%. Our experience is that the ventilation system is frequently a major source of microbial contamination. Coils, condensate pans, wet filters, and interior fiberglass lining in ductwork can all be potent amplification sites for microbes.
A major concern is that any hvac cleaning must be done in strict accordance with procedures designed to both remove the contamination in the system while completely collecting the debris, protecting the cleaning worker, and preventing a “blowback” of loosened debris into the occupied spaces. We have seen numerous instances where poor or careless duct cleaning actually created a much more serious contamination problem than existed previously. Because duct cleaning is largely an unregulated business, the customer has little assurance of a quality project, particularly if he or she does not fully understand the key issues in the cleaning process. Currently the industry attempts to impose its own quality controls, largely through the National Air Duct Cleaners Association (NADCA). Members tend to be more scrupulous regarding process and quality controls because NADCA has minimum experience requirements and requires periodic testing and recertification.
Increased ventilation rates will dilute microbes and reduce their overall concentrations, both through increased fresh outside air supply and increased exhaust. Studies have shown a relationship between improved air filtration, viable organism concentrations, and patient infection rates. In one study, as ventilation rates increased, infection rates decreased proportionately up to a baseline minimum infection rate at a ventilation rate of 35 cfm/person. For reference purposes, ASHRAE-recommended ventilation rates are shown in the table. The table shows that the recommended ventilation rates have tended to increase over time. This table illustrates both the importance of having adequate ventilation and the critical need for properly balanced air supplies.
Proper pressurization, to prevent exfiltration of pathogens to non-patient areas, is absolutely essential. But there can be significant energy penalties for increasing ventilation. Costs for heating, cooling, humidification, dehumidification, and filtration can be substantial and not the most desirable solution for an industry already under severe cost-control pressures.
“Source control,” which in this case refers to isolating infectious patients, is already in practice in virtually every hospital, and carries a substantial price. Individually housing patients in highly ventilated and filtered, segregated rooms is an expensive proposition. Hospital-wide, this type of isolation strategy is too costly to be practical.
Source control of toxic and hazardous substances has been improved in recent years in a number of ways. Toxic solvents have been replaced by less toxic substitutes that perform as well as the older products. Isolation hoods and clean benches are being used more frequently for routine manipulations of samples and drug treatments. Some processes have been “miniaturized” so that smaller quantities of sample and process chemicals are needed to achieve the same test result.
The use of personal protective equipment, such as hood-helmet operating systems, have increasingly been employed, both voluntarily and by mandate of the Centers for Disease Control (CDC) and/or OSHA. Because such controls are not strictly hvac devices, they will not be examined in detail here. It is important to note, however, that, in general, OSHA prefers the use of permanently engineered process control systems to minimize personal exposures rather than reliance on personal protective equipment that could fail with dire consequences.
The Case for FiltrationAnother alternative is filtration. Our view is that filtration should be the foremost weapon in dealing with indoor air quality in hospitals. Because the vast majority of microbes are associated with particles, HEPA filtration becomes an attractive solution to preventing spread of infection.
HEPA filters are, by industry definition, 99.97% effective against particles in the 0.3-micron size range. Thus HEPA filters are effective against bacteria that tend to be 0.3 microns and larger. TB bacteria tend to agglomerate in clumps averaging 1.5 microns and should be effectively controlled by HEPA filters. Ultra Low Penetrating Air (ULPA) filters, even more efficient at 99.997% removal, are increasingly becoming the standard for critical hospital treatments.
The use of UVGI, a technology which has been used since the 1940s, seems to have gathered renewed interest in hospital and even residential settings in very recent years. The efficacy of this technology cannot be as well predicted as filtration for any particular environment, yet it is clear that UVGI does reduce airborne bacteria concentrations to one degree or another. UVGI does not, however, appear to be very effective against fungal spores.
The configuration in which UVGI is used appears to influence its effectiveness. One common application is the use of UVGI in return-air duct systems to irradiate organisms in the return air stream. The overall level of contamination in the air, airflow rates, type of system, and frequency of cleaning of the light source, all appear to be critical factors influencing efficiency. Such systems tend to get dirty and need frequent cleaning to maintain optimal efficiency.
Another UVGI configuration is the patient-room wall or ceiling-mounted unit. In this application, the UV light source is directed into the room to kill organisms floating in the air. The efficacy varies widely depending on ventilation rate, activity in the room, room bioburden loading, and other factors. One concern appears to be the potential for thickening of the cornea of the eye following long-term exposure to UV light sources.