UVC For Controlling the Spread of Tuberculosis

Efficacy of UVC for Tuberculosis (TB) Control

Airborne transmission of Mycobacterium tuberculosis and other infectious agents within indoor environments has been a recognized hazard for decades. Engineering controls such as ventilation and negative pressure have been helpful for control of tuberculosis (TB) transmission in high risk settings such as hospital isolation rooms. Increasing costs associated with providing ventilation has prompted renewed interest in other means to remove airborne infectious agents from room air, such as the application of ultraviolet germicidal irradiation (UVGI). One application of UVGI is to irradiate the upper part of a room while minimizing radiation exposure to persons in the lower part of the room. Data has been available showing that UVGI has the potential to be a useful engineering control for TB. The 1994 CDC TB Guidelines (Centers for Disease Control and Prevention, 1994) relied primarily on upper room air UVGI studies over 30 years old when guidelines were written for its use as an engineering control measure to mitigate the transmission of airborne M. tuberculosis. Knowledge gaps still remained in regard to the impacts of environmental factors such as air mixing, relative humidity and various other parameters on the efficacy of upper-room air UVGI. In addition, no room studies had been conducted using modern UVGI fixtures and bulbs. Thus questions still remain on the best approach to install UVGI in real settings. The aim of the study was to systematically investigate the conditions under which UVGI can be expected to mitigate the spread of tuberculosis. Completion of this work has significantly improved our fundamental understanding of the efficacy of upper room air UVGl systems and will facilitate their design, optimization and implementation on a practical scale.

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TB Transmission
TB is transmitted through the air. A person with TB disease of the lungs or larynx can release droplets containing Mycobacterium tuberculosis (M. tb) into the air by coughing, sneezing, talking, or breathing. These droplets, called droplet nuclei, can cause TB infection if inhaled by anyone who shares air with the person who has TB.

Ultraviolet Germicidal Irradiation - UVGI
Ultraviolet Germicidal Irradiation - UVGI is the use of a type of UV radiation, known as UVC, which has been shown to kill or inactivate M. tb in air. Ultraviolet Germicidal Irradiation - UVGI is generated by specially designed air cleaners using uvc lamps that often look something like a fluorescent light. There are two ways that UV lamps are used in TB control:
• Upper-room UVGI is the use of Ultraviolet Germicidal Irradiation lamps directly in a room where there is a risk of M. tb being transmitted. It is a useful infection control technique for crowded spaces that may be occupied by a person with TB, such as prison day rooms, homeless shelters, and waiting rooms.
• In-duct UVGI is the use of UVGI lamps inside an air duct or air cleaner to disinfect air before it is recirculated. It is a useful upgrade for mechanical systems that recirculate air from high-risk congregate areas that may be occupied by a person with TB. However, in-duct UVGI is not equivalent to direct exhaust or high efficiency particulate air (HEPA) filtration for isolation rooms and high-risk procedure rooms.

Upper-Room UVGI
Upper-room UVGI uses lamps mounted at an elevation of seven or more feet. The fixtures are designed so that upper-room air is irradiated and disinfected. Cleaned air mixes with the air in the lower part of the room and dilutes infectious particles. Radiation levels in the lower parts of the room should be measured to verify that they
are within recommended parameters. Care should be taken in the design, installation, and maintenance of upper-room UVGI because of safety concerns. Also, effectiveness can vary and every installation is unique.

In-Duct UVGI
In-duct UVGI uses lamps mounted inside a duct perpendicular to airflow. An appropriately designed, installed, and maintained in-duct UVGI system should effectively disinfect most recirculated air. This will therefore significantly increase the effectiveness of the recirculating mechanical ventilation system in reducing the risk of M. tb transmission. The UV intensities of lamps used inside a duct can be, and should be, greater than
lamps used for upper-room UVGI. This is because the risk of UV overexposure is limited. For a given airflow, the number and spacing of the lamps is selected to ensure that air in the duct is exposed to sufficient radiation. The exposure depends on the intensity of the radiation and the time of exposure. A duct access door should be provided so that the lamps can be cleaned, checked, and replaced. To prevent exposure to the lamps, electrical interlock should shut off the lamps whenever the duct access door is open. In-duct UVGI is also used in self-contained air cleaning units.

Safety Concerns
UVGI can cause temporary harm to the eyes and skin. However, newer fixture designs and compliance with guidelines can make UVGI use safe and effective. Whenever UVGI is used, precautions should be taken to alert and protect staff and clients. Staff should also receive appropriate education. Warning signs in all appropriate
languages should be posted on fixtures and wherever UVGI is used. For example:

Routine Upkeep
Wherever UVGI is used, a routine maintenance program should be implemented to ensure that lamps are checked and replaced regularly. Lamps should be replaced once a year or as directed by the manufacturer.

WAC 246-324-190  Provisions for patients with tuberculosis.  A licensee providing inpatient services for patients with suspected or known infectious tuberculosis shall:
     (1) Design patient rooms with:
     (a) Ventilation to maintain a negative pressure condition in each patient room relative to adjacent spaces, except bath and toilet areas, with:
     (i) Air movement or exhaust from the patient room to the out-of-doors with the exhaust grille located over the head of the bed;
     (ii) Exhaust at the rate of six air changes per hour; and
     (iii) Make-up or supply air from adjacent ventilated spaces for four or less air changes per hour, and tempered outside air for two or more air changes per hour;
     (iv) Ultraviolet generator irradiation as follows:
     (A) Use of ultraviolet fluorescent fixtures with lamps emitting wave length of 253.7 nanometers;
     (B) The average reflected irradiance less than 0.2 microwatts per square centimeter in the room at the five foot level;
     (C) Wall-mount type of fixture installed over the head of the bed, as close to the ceiling as possible to irradiate the area of the exhaust grille and the ceiling; and
     (D) Lamps changed as recommended by the manufacturer; and
     (b) An adjoining bathroom and toilet room with bedpan washer; and
     (2) Provide discharge information to the health department of the patient's county of residence.

UVC Controlling The Spread Of Tuberculosis