UV light proven as new tool against TB
Blue zone’ inactivates bacteria in room
Ultraviolet (UV) light is an effective way to inactivate tuberculosis and prevent transmission in hospitals, according to a study sponsored by the National Institute for Occupational Safety and Health (NIOSH) in Cincinnati.
The use of UV light as an infection control tool has been controversial. This is the first study to demonstrate the effectiveness of UV light and to test different factors that may affect its functionality, says Millie Schafer, PhD, a research chemist with NIOSH who coordinated the project.
"It is an engineering control in its own right. We feel we have validated it as that," she says.
UV light may be especially useful in areas where tuberculosis patients have not yet been diagnosed and isolated, such as waiting areas, the registration area, or the emergency department.
"When you have a case that you know is TB, I think you need to have a negative pressure," says Shelly Miller, PhD, assistant professor in the department of mechanical engineering at the University of Colorado at Boulder. Miller was the principal investigator for the study.
Although the study focused on tuberculosis, it may have implications for preventing the transmission of other types of diseases. "Different organisms are susceptible to UV at different strengths," says Miller. "You want to make sure that the UV you’re putting in the room is enough irradiation to inactivate the bacteria you’re looking at. TB turns out to be a fairly susceptible to UV."
It’s not known whether UV light would be effective in inactivating the virus that causes severe acute respiratory syndrome. "Very, very little has been done with using UV to inactivate airborne viruses" because it is so difficult to aerosolize viruses, says Miller. She and her colleagues are designing a study to test ultraviolet light with viruses, she says.
Although the antibacterial effects of UV light have been acknowledged for years, it wasn’t easy to prove that it works. It took five years to design and conduct the study. Miller and her colleagues tested three bacteria that they could aerosolize: Mycobacterium parafortuitum, Mycobacterium bovis (a TB surrogate), and Bacillus subtilis.
Mark Hernandez, an environmental microbiologist at the University of Colorado, designed a method to sample and measure the inactivation of the bacteria. The researchers then created a simulated hospital room, with two to eight air changes per hour with a slight negative pressure. A manikin, heated to replicate body temperature, represented the patient. "We wanted it to be as close to a real health care room as possible," says Miller.
The UV system consisted of five lamps: one in each corner with bulbs totaling 36 watts and one in the center with bulbs totaling 72 watts. NIOSH will issue technical information on how to properly use UV light to inactivate bacteria.
Here are some factors that influence the effectiveness of the technology:
- Placement of bulbs. The lights must be evenly dispersed in the ceiling to create a "blue zone" where the bacteria will be inactivated, Schafer says. When they were concentrated in one part of the room, the system was less effective. The system should have a louvered fixture to allow the air to circulate near the bulbs but to protect health care workers in the room from the radiation. The ceiling also should be at least 8 feet high, she says.
- Mixing of air. Researchers used a fan to make sure the air circulated and reached the "blue zone." This can be especially important in some climates. For example, during the winter, heated air will rise and stay toward the ceiling, preventing the bacteria from reaching the UV lights.
- Ventilation. UV light can enhance infection control in a negative-pressure room. But the more frequent the air changes, the less effective the UV system will be in inactivating bacteria. "Sometimes, if you have a lot of ventilation, you might decide not to spend the money to put the UV in that space. You might decide to put it in a space where you’re not getting as much ventilation as you’d like," MIller says.
- Maintenance. Over time, dust will build up on the lamps and decrease the effectiveness of the system. "You’ll need to check them every so often to make sure they’re still operating at an acceptable level," she says. UV levels also should be monitored to make sure health care workers are not exposed to harmful levels.
The design of the UV system is critical, says Schafer. "Just walking in and throwing a bulb up on the wall, saying we have UV [germicidal irradiation] is not what we would be telling people to do." UV also cannot protect health care workers while they are in close contact with patients. Personal protective equipment still will be essential, she adds.
Recommended reading
1. Peng X, Peccia J, Fabian P, et al. Efficacy of ultraviolet germicidal irradiation of upper-room air in inactivating airborne bacterial spores and mycobacteria in full scale studies. Atmospheric Environment 2003; 37:405-419.
Ultraviolet light is an effective way to inactivate tuberculosis and prevent transmission in hospitals, according to a study sponsored by the National Institute for Occupational Safety and Health (NIOSH) in Cincinnati.You have reached your article limit for the month. Subscribe now to access this article plus other member-only content.
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