HIV This Week

Escombe AR, Moore DA, Gilman RH, Navincopa M, Ticona E, Mitchell B, Noakes C, Martínez C, Sheen P, Ramirez R, Quino W, Gonzalez A, Friedland JS, Evans CA. Upper-room ultraviolet light and negative air ionization to prevent tuberculosis transmission. PLoS Med. 2009;6(3):e43.

Institutional tuberculosis (TB) transmission is an important public health problem highlighted by the HIV pandemic and the emergence of multidrug- and extensively drug-resistant TB. Effective TB infection control measures are urgently needed. Escombe et al 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. For 535 consecutive days, exhaust air from an HIV-TB ward in Lima, Peru, 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. In conclusion, 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.

Editors’ note: Using the guinea pig air sampling model of the 1950s to advance further their DNA fingerprinting study which showed that 8.5% of 118 TB patients were responsible for 98.9% of the guinea pig infections (see issue 59 of HIV This Week), these authors turned their attention to preventing TB transmission. This is the first controlled evaluation assessing the effects on airborne TB transmission in a clinical setting of upper-room ultraviolet (UV) light that kills M. tuberculosis and negative ionization which gives airborne particles a charge that makes them stick to surfaces. Despite the high humidity of Lima (70 to 90%) which would affect UV germicidal efficacy, upper-room UV light had a marked effect reducing both TB infection (70%) and disease (54%). Although these are guinea pig studies, the evidence for this environmental control measure is strong. Upper-room UV lighting is relatively low cost compared to mechanical ventilation and should be expertly installed now in all waiting rooms, out-patient and emergency departments, and antiretroviral treatment facilities where undiagnosed and untreated TB patients are likely to be found. Designing simple UV fixtures for low-resource settings will facilitate scale-up further.

LoBue P. Extensively drug-resistant tuberculosis. Curr Opin Infect Dis. 2009;22(2):167-73.

The purpose of this review was to describe the origin, epidemiology, diagnosis, treatment, prevention, and control of extensively drug-resistant tuberculosis (XDR TB). XDR TB is defined as the occurrence of TB in persons whose Mycobacterium tuberculosis isolates are resistant to isoniazid and rifampin and to any fluoroquinolone and at least one of three injectable second-line drugs (i.e., amikacin, kanamycin, or capreomycin). As of June 2008, XDR TB has been found in 49 countries including the United States. It generally takes several weeks to detect XDR TB using conventional culture-based methods, although some progress is being made in developing rapid molecular tests. Treatment for XDR TB is difficult, usually requiring at least 18-24 months of four to six second-line anti-TB drugs. Treatment success rates are generally 30-50%, with very poor outcomes in HIV-infected patients. Management of contacts to infectious XDR TB patients is complicated by the lack of a proven effective treatment for XDR latent tuberculosis infection. XDR TB is an emerging global health threat. The disease is difficult and expensive to diagnose and treat, and outcomes are frequently poor. New rapid diagnostic tests and new classes of anti-TB drugs are needed to successfully combat this global problem.

Editors’ note: Following the death in 2006 in KwaZulu Natal of 52 of 53 patients diagnosed with XDR-TB (median survival of 16 days and 85% having acquired resistant TB rather than having developed it while under treatment), consultations were held, the definition of XDR-TB was changed, and WHO established a Global Task Force on XDR-TB. In 2007, WHO produced an eight-objective global response plan for MDR- and XDR-TB and published in 2008 its first resistance report to include XDR-TB. XDR-TB is most common in terms of absolute numbers in Eastern Europe and the former Soviet Republics of Central Asia. Given that MDR-TB is estimated to have increased from 270,000 cases in 2000 to 490,000 cases in 2006 and XDR-TB is estimated to represent approximately 7% of these, XDR-TB is deemed to be on the rise. The growing problem of anti-TB drug resistance and the high prevalence of HIV among TB patients in certain regions, particularly in sub-Saharan Africa, underscore the urgency of developing new TB resistance testing tools and new anti-TB treatments.

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