By David R. Linamen, PE, CIPE
In1994, the Centers for Disease Control and Prevention (CDC) adopted Guidelinesfor Preventing the Transmission of TB in Healthcare Facilities in an attemptto minimize the risk that TB might be passed from patients to healthcare workers(HCWs) and visitors. Although upper room ultraviolet germicidal irradiation (UVGI)is noted in the guidelines as having some effectiveness in reducing viable TBbacteria in healthcare facilities, the primary focus of the guidelines concernsventilation systems. The guidelines establish 12 air changes per hour (ACH) as aminimum standard for new or remodeled rooms intended to house TB patients, while6 ACH is established as the absolute minimum airflow rate for existingfacilities.
Recent research conducted at the National Institutes of Health (NIH) byFarhad Memarzadeh, MD, with assistance from Andrew Manning, MD, indicates thatUVGI, used in the proper configuration with adequate ventilation flow rate, canhave a significant impact on reducing the number of viable TB bacteria in apatient room. Memarzadeh and Manning also found that the UVGI can reduce thetotal airflow required, resulting in a first-cost savings in the ventilationsystem, as well as an overall operational cost savings because of the reducedair change requirement. This study further indicates that wintertime baseboardheating in a TB isolation room, in conjunction with a properly arrangedventilation system and effective UVGI, can significantly reduce the number ofviable particles in the room. The following summarizes the procedures and someof the more notable results from this research.
The research utilized computational fluid dynamics (CFD) to model the effectof airflow patterns on the distribution and removal of TB bacteria from patientrooms. As part of this research, algorithms were developed to track the bacteriathrough the room so the UV dosage affecting these particles could be calculated.As a result, the number of bacteria removed by the ventilation system, thenumber of bacteria destroyed by UV, and the number of remaining viable bacteriain the room at any time could be determined. The study evaluated the effect ofseveral conditions including ventilation flow rate, supply temperature andexternal ambient condition, exhaust inlet location, baseboard heating influencein winter, pressurization of the patient room relative to surroundings, andlocation and intensity of UV lamps in the room. The study evaluated 40 differentroom configurations and three different combinations of lamp intensity andlocation. The study produced the following conclusions:
To date, it is not known if the CDC intends to revise the Guidelinesto reflect the findings from this study. A detailed summary of the studyprocedure and the results are included in the Handbook on Assessing theEfficacy of Ultraviolet Germicidal Irradiation Ventilation in RemovingMycobacterium Tuberculosis, available from the NIH, Bethesda, Md. (ISBN0-16-061398-1).
David R. Linamen, PE, CIPE, is a principal with Burt Hill Kosar RittelmannAssociates, an architectural and engineering firm with locations in Pittsburgh,Philadelphia, and Butler, Penn; Boston, Mass; Cleveland, Ohio; and Washington,DC.
1. State the requirements of OSHA's Needlestick Prevention Act.
2. Identify safety criteria to use when selecting safety devices forhealthcare workers.
3. Recognize the cost/benefit issues in purchasing equipment and suppliesthat meet infection control standards.