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      Upper-Room Ultraviolet Light and Negative Air Ionization to Prevent Tuberculosis Transmission


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          Institutional 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 Findings

          For 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.


          Upper-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.


          Using a guinea-pig detection model, Rod Escombe and colleagues find that upper-room UV lamps in hospital rooms can substantially reduce airborne transmission of Mycobacterium tuberculosis.


          Editors' Summary

          Tuberculosis—a contagious infection, usually of the lungs—kills nearly 2 million people annually. It is caused by Mycobacterium tuberculosis, bacteria that are spread in airborne droplets when people with tuberculosis cough or sneeze. Most people infected with M. tuberculosis do not become ill—their immune system contains the infection. However, the bacteria remain dormant within the body and can cause disease years later if immunity declines because of, for example, infection with human immunodeficiency virus (HIV), the cause of acquired immunodeficiency syndrome (AIDS). The symptoms of tuberculosis include a persistent cough, weight loss, and night sweats. Infection with M. tuberculosis is diagnosed using the tuberculin skin test. Tests for tuberculosis itself include chest X-rays and sputum cultures (in which bacteriologists try to grow M. tuberculosis from mucus brought up from the lungs by coughing). Tuberculosis can usually be cured by taking several powerful antibiotics daily for several months. Drug-resistant tuberculosis is much harder to cure, requiring multiple second-line antibiotics for up to two years or more. Tuberculosis transmission can be reduced by, for example, hospitalizing people with tuberculosis in isolation wards in which negative-pressure mechanical ventilation is used to reduce the concentration of infectious airborne droplets.

          Why Was This Study Done?

          After the development of antibiotics capable of killing M. tuberculosis in the mid 20th century, it seemed that tuberculosis would become a disease of the past. But in the mid 1980s, drug-resistant M. tuberculosis strains began to emerge, the HIV/AIDS epidemic took hold, and tuberculosis resurged to today's worrying levels. New ways of reducing tuberculosis transmission, particularly in health care settings and in resource-limited settings, are now urgently needed. The need for effective infection control measures is especially urgent in HIV care programs where highly susceptible individuals frequently mix with people with tuberculosis. In this study, the researchers use a guinea pig air-sampling model (which was first used in the 1950s to show that tuberculosis is an airborne infection) to investigate whether upper-room ultraviolet (UV) lights in patient rooms and negative air ionization can prevent airborne tuberculosis transmission. UV light kills M. tuberculosis; negative ionization gives airborne particles a charge that makes them stick to surfaces.

          What Did the Researchers Do and Find?

          The researchers exposed a group of control guinea pigs kept in a special air-sampling enclosure to untreated air from an HIV–TB ward in Lima (Perú). Another group of animals (the UV group) breathed air from the same ward, but only on the days that UV lights suspended near the ward's ceiling were turned on, together with mixing fans to mix up the room air. The “ionizer group” had a negative ionizer switched on in their enclosure when they were exposed to ward air (each group of animals was exposed to ward air every other day). The animals were tested monthly with the tuberculin skin test and all were examined for tuberculosis disease when they became infected with tuberculosis or at the end of the 535-day experiment. 35% of the control animals, 14% of the ionizer group animals, and 9.5% of the UV group animals developed M. tuberculosis infections. Tuberculosis disease was found in 8.6% of the control animals but in only 4.3% and 3.6% of the animals in the ionizer and UV groups, respectively. A “time-to-event analysis” also showed that UV lights and ionizers reduced tuberculosis infection and disease. Finally, an analysis of the data using an airborne infection model indicated that ionizers and UV lights prevented 60% and 70% of tuberculosis infections, respectively.

          What Do These Findings Mean?

          These findings indicate that upper-room UV lights, combined with adequate air mixing, or negative air ionization with special large-scale ionizers can prevent most airborne tuberculosis transmission to guinea pigs exposed to hospital room air. The effectiveness of these approaches in reducing tuberculosis transmission between people is likely to be similar, although remains to be tested. Nevertheless, this first study of the effect of upper-air UV light and of negative air ionization on airborne transmission in a clinical setting suggests that both approaches could be potentially important tuberculosis infection control measures. Furthermore, the UV light approach might provide a relatively low-cost intervention for possible use in waiting rooms and other overcrowded settings where patients with undiagnosed, untreated tuberculosis—individuals who tend to be highly infectious—are likely to come into contact with other susceptible patients, health care workers, and visitors.

          Additional Information.

          Please access these Web sites via the online version of this summary at http://dx.doi.org/10.1371/journal.pmed.1000043.

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          Most cited references51

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          Guidelines for preventing the transmission of Mycobacterium tuberculosis in health-care settings, 2005.

          In 1994, CDC published the Guidelines for Preventing the Transmission of Mycobacterium tuberculosis in HealthCare Facilities, 1994. The guidelines were issued in response to 1) a resurgence of tuberculosis (TB) disease that occurred in the United States in the mid-1980s and early 1990s, 2) the documentation of several high-profile health-care--associated (previously termed "nosocomial") outbreaks related to an increase in the prevalence of TB disease and human immunodeficiency virus (HIV) coinfection, 3) lapses in infection control practices, 4) delays in the diagnosis and treatment of persons with infectious TB disease, and 5) the appearance and transmission of multidrug-resistant (MDR) TB strains. The 1994 guidelines, which followed statements issued in 1982 and 1990, presented recommendations for TB infection control based on a risk assessment process that classified health-care facilities according to categories of TB risk, with a corresponding series of administrative, environmental, and respiratory protection control measures. The TB infection control measures recommended by CDC in 1994 were implemented widely in health-care facilities in the United States. The result has been a decrease in the number of TB outbreaks in health-care settings reported to CDC and a reduction in health-care-associated transmission of Mycobacterium tuberculosis to patients and health-care workers (HCWs). Concurrent with this success, mobilization of the nation's TB control programs succeeded in reversing the upsurge in reported cases of TB disease, and case rates have declined in the subsequent 10 years. Findings indicate that although the 2004 TB rate was the lowest recorded in the United States since national reporting began in 1953, the declines in rates for 2003 (2.3%) and 2004 (3.2%) were the smallest since 1993. In addition, TB infection rates greater than the U.S. average continue to be reported in certain racial/ethnic populations. The threat of MDR TB is decreasing, and the transmission of M. tuberculosis in health-care settings continues to decrease because of implementation of infection-control measures and reductions in community rates of TB. Given the changes in epidemiology and a request by the Advisory Council for the Elimination of Tuberculosis (ACET) for review and update of the 1994 TB infection control document, CDC has reassessed the TB infection control guidelines for health-care settings. This report updates TB control recommendations reflecting shifts in the epidemiology of TB, advances in scientific understanding, and changes in health-care practice that have occurred in the United States during the preceding decade. In the context of diminished risk for health-care-associated transmission of M. tuberculosis, this document places emphasis on actions to maintain momentum and expertise needed to avert another TB resurgence and to eliminate the lingering threat to HCWs, which is mainly from patients or others with unsuspected and undiagnosed infectious TB disease. CDC prepared the current guidelines in consultation with experts in TB, infection control, environmental control, respiratory protection, and occupational health. The new guidelines have been expanded to address a broader concept; health-care--associated settings go beyond the previously defined facilities. The term "health-care setting" includes many types, such as inpatient settings, outpatient settings, TB clinics, settings in correctional facilities in which health care is delivered, settings in which home-based health-care and emergency medical services are provided, and laboratories handling clinical specimens that might contain M. tuberculosis. The term "setting" has been chosen over the term "facility," used in the previous guidelines, to broaden the potential places for which these guidelines apply.
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            Risk of tuberculosis infection and disease associated with work in health care settings.

            Tuberculosis (TB) in health care workers (HCWs) was not considered a serious problem following the advent of effective antibiotic therapy. Interest was re-stimulated by the occurrence of several major nosocomial outbreaks. We have reviewed the available published literature regarding prevalence and incidence of TB infection and disease among HCWs in countries categorised by mean income. We included studies published in English since 1960 from low- and middle-income countries (LMICs) and since 1990 from high-income countries (HICs). We excluded outbreak reports and studies based only on questionnaires. The median prevalence of latent TB infection (LTBI) in HCWs was 63% (range 33-79%) in LMICs and 24% in HICs (4-46%). Among HCWs from LMICs, LTBI was consistently associated with markers of occupational exposure, but in HICs it was more often associated with non-occupational factors. The median annual incidence of TB infection attributable to health care work was 5.8% (range 0-11%) in LMICs and 1.1% (0.2-12%) in HICs. Rates of active TB in HCWs were consistently higher than in the general population in all countries, although findings were variable in HICs. Administrative infection control measures had a modest impact in LMICs, yet seemed the most effective in HICs. TB remains a very important occupational risk for HCWs in LMICs and for workers in some institutions in HICs. Risk appears particularly high when there is increased exposure combined with inadequate infection control measures.
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              Transmission of tuberculosis in New York City. An analysis by DNA fingerprinting and conventional epidemiologic methods.

              The incidence of tuberculosis and drug resistance is increasing in the United States, but it is not clear how much of the increase is due to reactivation of latent infection and how much to recent transmission. We performed DNA fingerprinting using restriction-fragment-length polymorphism (RFLP) analysis of at least one isolate from every patient with confirmed tuberculosis at a major hospital in the Bronx, New York, from December 1, 1989, through December 31, 1992. Medical records and census-tract data were reviewed for relevant clinical, social, and demographic data. Of 130 patients with tuberculosis, 104 adults (80 percent) had complete medical records and isolates whose DNA fingerprints could be evaluated. Isolates from 65 patients (62.5 percent) had unique RFLP patterns, whereas isolates from 39 patients (37.5 percent) had RFLP patterns that were identical to those of an isolate from at least 1 other study patient; the isolates in the latter group were classified into 12 clusters. Patients whose isolates were included in one of the clusters were inferred to have recently transmitted disease. Independent risk factors for having a clustered isolate included seropositivity for the human immunodeficiency virus (HIV) (odds ratio for Hispanic patients, 4.31; P = 0.02; for non-Hispanic patients, 3.12; P = 0.07), Hispanic ethnicity combined with HIV seronegativity (odds ratio, 5.13; P = 0.05), infection with drug-resistant tuberculosis (odds ratio, 4.52; P = 0.005), and younger age (odds ratio, 1.59; P = 0.02). Residence in sections of the Bronx with a median household income below $20,000 was also associated with having a clustered isolate (odds ratio, 3.22; P = 0.04). In the inner-city community we studied, recently transmitted tuberculosis accounts for approximately 40 percent of the incident cases and almost two thirds of drug-resistant cases. Recent transmission of tuberculosis, and not only reactivation of latent disease, contributes substantially to the increase in tuberculosis.

                Author and article information

                Role: Academic Editor
                PLoS Med
                PLoS Medicine
                Public Library of Science (San Francisco, USA )
                March 2009
                17 March 2009
                : 6
                : 3
                [1 ] Department of Infectious Diseases & Immunity, Imperial College London, United Kingdom
                [2 ] Wellcome Centre for Clinical Tropical Medicine, Imperial College London, United Kingdom
                [3 ] Asociación Benéfica PRISMA, Lima, Perú
                [4 ] Universidad Peruana Cayetano Heredia, Lima, Perú
                [5 ] Johns Hopkins Bloomberg School of Public Health, Baltimore, Maryland, United States of America
                [6 ] Hospital Nacional Dos de Mayo, Lima, Perú
                [7 ] Universidad Nacional Mayor San Marcos, Lima, Perú
                [8 ] Agricultural Research Service, U.S. Department of Agriculture, Washington, D. C., United States of America
                [9 ] School of Civil Engineering, University of Leeds, Leeds, United Kingdom
                University College London, United Kingdom
                Author notes
                * To whom correspondence should be addressed. E-mail: rod.escombe@ 123456imperial.ac.uk
                08-PLME-RA-1399R4 plme-06-03-09
                This is an open-access article distributed under the terms of the Creative Commons Public Domain declaration, which stipulates that, once placed in the public domain, this work may be freely reproduced, distributed, transmitted, modified, built upon, or otherwise used by anyone for any lawful purpose.
                Page count
                Pages: 12
                Research Article
                Infectious Diseases
                Public Health and Epidemiology
                Respiratory Medicine
                Custom metadata
                Escombe AR, Moore DAJ, Gilman RH, Navincopa M, Ticona E, et al. (2009) Upper-room ultraviolet light and negative air ionization to prevent tuberculosis transmission. PLoS Med 6(3): e1000043. doi: 10.1371/journal.pmed.1000043



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