Environmental Control for Tuberculosis: Basic Upper-Room Ultraviolet Germicidal Irradiation Guidelines for Healthcare Settings

摘要

Although the number of cases of tuberculosis (TB) in the United States has declined in the last several years, there is still a continuing need to protect healthcare workers and the public from risk of infection. One of the primary risks to healthcare workers and the public is exposure to persons with unsuspected or undiagnosed infectious TB. Exposures of this type may occur in areas such as waiting rooms, corridors, or emergency rooms in healthcare facilities (e.g., hospitals, correctional institutions, nursing homes, clinics). While mechanical ventilation systems may provide protection to workers in these situations, there are limitations such as environmental constraints, cost, and comfort considerations. In 1997, the Centers for Disease Control and Prevention (CDC), National Institute for Occupational Safety and Health (NIOSH) awarded a contract to the University of Colorado to evaluate the ability of a well-designed and thoroughly characterized upper-room ultraviolet germicidal irradiation (UVGI) system to kill or inactivate airborne mycobacteria. A number of parameters were evaluated during the study. These included (1) the irradiance level in the upper room that provides a UVGI dose over time that kills or inactivates an airborne surrogate of Mycobacterium tuberculosis, (2) how to best measure UVGI fluence levels, (3) the effect of air mixing on UVGI performance, (4) the relationship between mechanical ventilation and UVGI systems, (5) the effects of humidity and photoreactivation (PR), and (6) the optimum placement of UVGI fixtures. The completed research indicates that an appropriately designed and maintained upper-room UVGI system may kill or inactivate airborne TB bacteria and increase the protection afforded to healthcare workers while maintaining a safe level of UVGI in the occupied lower portion of the room. Additional research still needs to be done to better plan effective upper-room UVGI fixture installation considering variables such as air mixing and measurement of the average UV fluence rate in the upper room. However, sufficient laboratory information is now available to develop these guidelines. This document is designed to provide information to healthcare managers, facility designers, engineers, and industrial hygienists on the parameters necessary to install and maintain an effective upper-room UVGI system.