Guidelines for preventing transmission of M. tuberculosis in health-care settings and for environmental infection control in health-care facilities have been published previously.[71,72] These guidelines and this report can be used to educate correctional facility staff regarding use of environmental controls in TB infection-control programs.
Environmental controls should be implemented when the risk for TB transmission persists despite efforts to screen and treat infected inmates. Environmental controls are used to remove or inactivate M. tuberculosis in areas in which the organism could be transmitted. Primary environmental controls consist of controlling the source of infection by using local exhaust ventilation (e.g., hoods, tents, or booths) and diluting and removing contaminated air by using general ventilation. These controls help prevent the spread and reduce the concentration of airborne infectious droplet nuclei (see Glossary). Environmental controls work in conjunction with administrative controls such as isolation of inmates with suspected TB disease detected through screening (see Glossary). Secondary environmental controls consist of controlling the airflow to prevent contamination of air in areas adjacent to the source (AII rooms) and cleaning the air (using a HEPA filter or ultraviolet germicidal irradiation [UVGI]) to increase the number of equivalent ACH.¶ The efficiency of different primary or secondary environmental controls varies; details concerning the application of these controls to prevent transmission of M. tuberculosis in health-care settings have been published previously. To be effective, secondary environmental controls should be used and maintained properly, and their strengths and limitations should be recognized. The engineering design and operational efficacy parameters for UVGI as a secondary control measure (i.e., portable UVGI units, upper-room air UVGI, and in-duct UVGI) continue to evolve and require special attention in their design, selection, and maintenance.
Exposure to M. tuberculosis within correctional facilities can be reduced through the effective use of environmental controls at the source of exposure (e.g., an infectious inmate) or in general areas. Source-control techniques can prevent or reduce the spread of infectious droplet nuclei into the air in situations in which the source has been identified and the generation of the contaminant is localized by collecting infectious particles as they are released. Use of these techniques is particularly prudent during procedures that are likely to generate infectious aerosols (e.g., bronchoscopy and sputum induction) and when inmates with infectious TB disease are coughing or sneezing.
Unsuspected and undiagnosed cases of infectious TB disease contribute substantially to disease transmission within correctional facilities. When attempting to control this type of transmission, source control is not a feasible option. Instead, general ventilation and air cleaning should be relied on for environmental control. General ventilation can be used to dilute the air and remove air contaminants and to control airflow patterns in AII rooms or other correctional facility settings. Air-cleaning technologies include mechanical air filtration to reduce the concentration of M. tuberculosis droplet nuclei and UVGI to kill or inactivate microorganisms so they no longer pose a risk for infection.
Ventilation systems for correctional facility settings should be designed, and modified when necessary, by ventilation engineers in collaboration with infection-control practitioners and occupational health staff. Recommendations for designing and operating ventilation systems in correctional facilities have been published.[48,49,74,75,76] The multiple types of and conditions for use of ventilation systems in correctional-facility settings and the individual needs of these settings preclude provision of extensive guidance in this report.
Incremental improvements in environmental controls (e.g., increasing the removal efficiency of an existing filtration system in any area) are likely to lessen the potential for TB transmission from persons with unsuspected or undiagnosed TB. This information should not be used in place of consultation with experts who can advise on ventilation system and air handling design, selection, installation, and maintenance. Because environmental controls will fail if they are not properly operated and maintained, routine training and education of infection-control and maintenance staff are key components to a successful TB infection-control program.
Inmates known or suspected of having TB disease should be placed in an AII room or AII cell that meets the design and operational criteria for airborne infection isolation described previously. Inmates deemed infectious should remain in isolation until treatment or further evaluation has ensured that they are noninfectious. Facilities without an on-site AII room should have a written plan for referring patients with suspected or confirmed TB to a facility that is equipped to isolate, evaluate, and treat TB patients.
New or renovated facilities should ensure that a sufficient number of AII rooms are available consistent with the facility risk assessment. Under rare circumstances, if an AII room is not available and the immediate transfer of the inmate with suspected infectious TB is not possible, the inmate should be housed temporarily in a room that has been modified to prevent the escape of infectious aerosols outside the TB holding area. The heating, ventilating, and air-conditioning (HVAC) system in this temporary TB holding area might have to be manipulated or augmented with auxiliary exhaust fans to create an inward flow of air that reduces the potential escape of infectious aerosols. If possible, air from these areas should be exhausted directly to the outdoors. If this is not feasible, the highest filtration efficiency compatible with the installed HVAC system should be used. Because TB droplet nuclei are approximately 1--5 micrometers in size, filtration efficiency should be evaluated for particles in that size range. Filter selection based on the American Society of Heating, Refrigerating and Air-Conditioning Engineers (ASHRAE) Standard 52.2 Minimum Efficiency Reporting Value (MERV)--rating efficiency tables can help in this evaluation. Secondary air cleaning techniques (portable air cleaners and UVGI) also can be used in these areas to increase effective air cleaning.
Aerosol-producing procedures should be performed in an area with a type of local exhaust ventilation that captures and removes airborne contaminants at or near their source without exposing persons in the area to infectious agents. Local exhaust devices typically use hoods. Two types of hoods are used: enclosing devices, in which the hood either partially or fully encloses the infectious source, and exterior devices, in which the infectious source is near but outside the hood. Fully enclosed hoods, booths, or tents are always preferable to exterior devices because of their superior ability to prevent contaminants from escaping.
Enclosing devices should have sufficient airflow to remove ≥99% of airborne particles during the interval between the departure of one patient and the arrival of the next. The time required to remove a given percentage of airborne particles from an enclosed space depends on 1) the ACH number, 2) the location of the ventilation inlet and outlet, and 3) the physical configuration of the room or booth. The time interval required to ensure the proper level of airborne contaminant removal from enclosing devices varies according to ACH ( Table 1 ). For example, if an enclosing device operates at six ACH, and the air inlet and exhaust locations allow for good air mixing, approximately 46 minutes would be required to remove 99% of the contaminated air after the aerosol-producing procedure has ended. Similarly, an additional 23 minutes (total time: 69 minutes) would be required to increase the removal efficiency to 99.9%. Doubling the ventilation rate decreases the waiting time by half.
General ventilation is used to 1) dilute and remove contaminated air, 2) control the direction of airflow in a correctional facility setting, and 3) control airflow patterns in rooms. Recommended ventilation rates for correctional facility settings are typically expressed in ACH. Ventilation recommendations for selected areas in new or renovated correctional facility settings should be followed ( Table 2 ). The feasibility of achieving a specific ventilation rate depends on the construction and operational requirements of the ventilation system and might differ for retrofitted and newly constructed facilities. The expense and effort of achieving a high ventilation rate might be reasonable for new construction but not be as feasible when retrofitting an existing setting.
Ventilation design guidance for correctional facilities and related areas has been published. This design guidance includes specific ventilation recommendations regarding total ventilation, filtration efficiency, and environmental design parameters. For minimum outdoor air supply recommendations, the guidance refers to ASHRAE Standard 62, Ventilation for Acceptable Indoor Air Quality. In 2004, ASHRAE revised and renumbered this standard to ANSI/ASHRAE Standard 62.1. For areas within correctional facilities that are not intended to contain persons with infectious TB, the recommended minimum outdoor air supply rates should meet or exceed those recommended in ANSI/ASHRAE Standard 62.1-2004. When risk analysis reveals an enhanced potential for undiagnosed cases of infectious TB, facility designers and owners may consider using higher supply rates of outdoor air (e.g., those recommended for areas within health-care facilities anticipated to contain infectious patients). Minimum outdoor air supply recommendations for health-care facilities have been published.[71,79] Because correctional areas frequently will not have an exact equivalent area within the health-care environment, the designer or owner should identify an analogous health-care area from which to choose the outdoor air supply recommendation. This selection should be made on the basis of occupant risk factors for TB, occupant activities, and occupant density within the area. For example, the intake, holding, and processing area of a higher risk correctional facility might be considered analogous to the emergency waiting room area in a health-care facility. In that case, the recommended outdoor air supply would be at least two ACH.
The direction of air movement relative to adjacent areas is necessary for the containment of contaminated air. Air within a correctional facility should flow to minimize exposure of others within the building ( Table 2 ). For example, air inside an AII room or cell should flow from the corridor and air-supply grille across the worker, then across that patient, and finally out of the room. To ensure that air is flowing from the corridor into an AII room or cell, smoke testing should be performed daily, even if the AII room or cell is equipped with a pressure-sensing device. Air flow (supply air and exhaust air) should be measured at least annually and compared with the designed air flow rates to ensure that optimal directional air flow and air exchange rates are being maintained ( Table 2 ).
Detailed information has been published regarding the selection, design, maintenance, and safety considerations associated with air cleaning methods (i.e., filtration and UVGI). Designers and end users should consult this information. Air removed from areas likely to contain infectious aerosols (e.g., AII cells, sputum collection and other procedure rooms, and intake areas) should be exhausted directly to the outdoors to ensure that it cannot immediately reenter the building or pose a hazard to persons outside, in accordance with applicable federal, state, and local regulations. If discharging air to the outside is not feasible, HEPA filters should be used to clean the air before returning to the general ventilation system. Such recirculation is acceptable only if the air is recirculated back into the same general area from which it originated.
For general population areas in which infectious aerosols are not anticipated but might be present (from persons with undiagnosed TB disease), total exhaust ventilation should be considered where and when the outdoor environmental conditions (temperature and humidity) are compatible with a single-pass system without undue energy or equipment costs. When recirculating air from these areas, the minimum ASHRAE-recommended level of filtration is a MERV-8 filter. However, CDC encourages selection and use of filters with higher MERV ratings to provide an incremental improvement in the protection afforded by this mechanism. The filtration system should be designed to prevent filter by-pass and to allow filter leakage testing and safe filter changes. A combination of air cleaning methods (e.g., MERV-rated filters and supplemental UVGI) may be used to increase effective air cleaning.
When used, UVGI should be applied in-duct (i.e., inside the ductwork of existing HVAC systems) or in the upper room of the area to be treated to ensure that organisms are inactivated. Upper-air systems should be designed, installed, and monitored to ensure both sufficient irradiation in the upper room to inactivate M. tuberculosis and safe levels of UVGI in the occupied space.
To be most effective, environmental controls should be installed, operated, and maintained correctly. Ongoing maintenance should be part of any written TB infection-control plan. The plan should outline the responsibility and authority for maintenance and address staff training needs.
Failure to maintain environmental control systems properly has adversely impacted TB control and prevention efforts at facilities throughout the United States. At one hospital, improperly functioning ventilation controls were believed to be a factor in the transmission of MDR TB disease to four persons (three patients and a correctional officer), three of whom died. In three other multihospital studies evaluating the performance of AII rooms, failure to routinely monitor air-pressure differentials (whether manually or through use of continuous monitoring devices) resulted in a substantial percentage of the rooms being under positive pressure.[81,82,83,84]
Correctional facilities should schedule routine preventive maintenance that covers all components of the ventilation systems (e.g., fans, filters, ducts, supply diffusers, and exhaust grilles) and any air-cleaning devices in use. Performance monitoring should be conducted to verify that environmental controls are operating as designed. Performance monitoring should include 1) directional airflow assessments using smoke tubes and use of pressure monitoring devices sensitive to pressures at 0.001 inch of water gauge and 2) measurement of supply and exhaust airflows to compare with recommended air change rates for the respective areas of the facility. Records should be kept to document all preventive maintenance and repairs.
Standard procedures should be established to ensure that 1) maintenance staff notify infection-control personnel before performing maintenance on ventilation systems servicing inmate-care areas and 2) infection-control staff request assistance from maintenance personnel in checking the operational status of AII cells and local exhaust devices (e.g., booths, hoods, and tents) before use. A protocol that is well written and followed will help to prevent unnecessary exposures of correctional facility staff and inmates to infectious aerosols. Proper labeling of ventilation system components (e.g., ducts, fans, and filters) will help identify air-flow paths. Clearly labeling which fan services a given area will help prevent accidental shutdowns. In addition, provisions should be made for emergency power to avoid interruptions in the performance of essential environmental controls during a power failure.
¶ ACH is the ratio of the volume of air entering the room or booth per hour to the volume of that room or booth. It equals the exhaust airflow (Q) in cubic feet per minute (cfm) divided by the volume of the room or booth (V) in cubic feet (ft3) multiplied by 60 minutes per hour, as expressed thus:
Morbidity and Mortality Weekly Report. 2006;55(27):1-44. © 2006 Centers for Disease Control and Prevention (CDC)
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Cite this: Prevention and Control of Tuberculosis in Correctional and Detention Facilities: Recommendations from CDC - Medscape - Jul 07, 2006.