Ultraviolet, or UV, light is electromagnetic radiation with a wavelength shorter than that of visible light; consequently, UV rays have higher frequencies and energies than light in the visible spectrum. UV light can damage DNA in cells and can thus kill most bacteria if present above certain levels. This same property, however, makes UV dangerous to humans, since UV light can damage DNA in skin cells and cause mutations that could eventually lead to the development of skin cancer.
Tuberculosis, or TB, currently ranks among the world's deadliest diseases, and roughly 2 million deaths are related to tuberculosis each year, according to the Centers for Disease Control. Since the bacterium is an airborne pathogen, some researchers have suggested that irradiating air in hospital wards and waiting rooms with ultraviolet light would help prevent transmission of the disease.
Tuberculosis is a common disease. The World Health Organization estimates one-third of the world's population is infected with TB. The immune system typically walls in the bacterium which then lies dormant, sometimes for many years. This condition is called a latent infection since there are no symptoms. Latent infections are not contagious. Only 5 to 10 percent of people with latent infections will actually go on to develop full-blown TB, at which point they can transmit the disease to others when they cough or sneeze, since droplets of sputum from a patient with an active infection often contain TB bacteria. TB is susceptible to some antibiotics, but recently some drug-resistant strains have emerged and become a serious public health concern in many countries.
Upper-Room UV Irradiation
Some researchers, like Dr. Rod Escombe of Imperial College London, have conducted studies that suggest UV light irradiation reduces the risk of TB transmission in hospital wards. The Centers for Disease Control has funded similar research as well, and some facilities like Boston's Pine Street Inn have actually installed upper-room UV systems. In order to avoid danger to patients and hospital workers, the UV lights fixtures are mounted high up in the room and face upwards so only the top portion of the room is irradiated. Ventilators then keep the air in the room circulating continually, so that many of the bacteria carried in microscopic droplets are eventually irradiated and killed.
In order for the system to work, it's crucial that the air in the room is well-mixed by appropriate ventilation and the dose of UV light must be enough to kill the bacteria. Humidity is also important, since high levels of humidity seem to impair effectiveness. Systems must also be designed so patient and employee exposure to dangerous UV rays is as minimal as possible.
A 2009 study published in the Public Library of Science at PLoS.org found that upper-room UV irradiation dramatically reduced transmission of TB from humans to guinea pigs, since guinea pigs are also susceptible to TB. The CDC guidelines on upper-room UV systems note, however, that further research is still needed to determine how effective upper-room systems truly are in combination with other measures.
- Centers for Disease Control: Tuberculosis
- World Health Organization: Tuberculosis
- "PLoS Medicine"; Upper-Room Ultraviolet Light and Negative Air Ionization to Prevent Tuberculosis Transmission; Escombe, Moore et al.; 2009.
- Centers for Disease Control: Basic Upper-Room Ultraviolet Irradiation
- Harvard Public Health Review: UV or Not UVrol: Basic Upper-Room Ultraviolet Irradiation, That is the TB Question
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