Date Published: March 17, 2009
Publisher: Public Library of Science
Author(s): A. Roderick Escombe, David A. J Moore, Robert H Gilman, Marcos Navincopa, Eduardo Ticona, Bailey Mitchell, Catherine Noakes, Carlos Martínez, Patricia Sheen, Rocio Ramirez, Willi Quino, Armando Gonzalez, Jon S Friedland, Carlton A Evans, Peter Wilson
Abstract: BackgroundInstitutional tuberculosis (TB) transmission is an important public health problem highlighted by the HIV/AIDS pandemic and the emergence of multidrug- and extensively drug-resistant TB. Effective TB infection control measures are urgently needed. We evaluated the efficacy of upper-room ultraviolet (UV) lights and negative air ionization for preventing airborne TB transmission using a guinea pig air-sampling model to measure the TB infectiousness of ward air.Methods and FindingsFor 535 consecutive days, exhaust air from an HIV-TB ward in Lima, Perú, was passed through three guinea pig air-sampling enclosures each housing approximately 150 guinea pigs, using a 2-d cycle. On UV-off days, ward air passed in parallel through a control animal enclosure and a similar enclosure containing negative ionizers. On UV-on days, UV lights and mixing fans were turned on in the ward, and a third animal enclosure alone received ward air. TB infection in guinea pigs was defined by monthly tuberculin skin tests. All guinea pigs underwent autopsy to test for TB disease, defined by characteristic autopsy changes or by the culture of Mycobacterium tuberculosis from organs. 35% (106/304) of guinea pigs in the control group developed TB infection, and this was reduced to 14% (43/303) by ionizers, and to 9.5% (29/307) by UV lights (both p < 0.0001 compared with the control group). TB disease was confirmed in 8.6% (26/304) of control group animals, and this was reduced to 4.3% (13/303) by ionizers, and to 3.6% (11/307) by UV lights (both p < 0.03 compared with the control group). Time-to-event analysis demonstrated that TB infection was prevented by ionizers (log-rank 27; p < 0.0001) and by UV lights (log-rank 46; p < 0.0001). Time-to-event analysis also demonstrated that TB disease was prevented by ionizers (log-rank 3.7; p = 0.055) and by UV lights (log-rank 5.4; p = 0.02). An alternative analysis using an airborne infection model demonstrated that ionizers prevented 60% of TB infection and 51% of TB disease, and that UV lights prevented 70% of TB infection and 54% of TB disease. In all analysis strategies, UV lights tended to be more protective than ionizers.ConclusionsUpper-room UV lights and negative air ionization each prevented most airborne TB transmission detectable by guinea pig air sampling. Provided there is adequate mixing of room air, upper-room UV light is an effective, low-cost intervention for use in TB infection control in high-risk clinical settings.
Partial Text: Tuberculosis (TB) infection control remains a public health priority, especially with the emergence of extensively drug-resistant strains . TB outbreaks have long been reported in congregate settings  including hospitals [3,4], homeless shelters , and correctional facilities . Nosocomial transmission and occupational TB are common in resource-limited settings, especially where TB and HIV are prevalent [7–9]. The expansion of HIV care programmes may inadvertently increase TB transmission by congregating highly susceptible individuals with those likely to have TB disease .
This is, to our knowledge, the first controlled evaluation of the effect of upper-room UV light or negative air ionization on airborne TB transmission in a clinical setting. By using a guinea pig air-sampling model to measure the TB infectiousness of air, we have demonstrated that both interventions prevented most TB transmission and are therefore potentially important TB infection control measures.