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

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.

The epidemiology, pathogenesis, transmission, diagnosis, and management of multidrug-resistant, extensively drug-resistant, and incurable tuberculosis

“…However, of the three technologies available to supplement or replace natural ventilation (at night, for example), germicidal ultraviolet air disinfection holds the greatest potential for sustainable effectiveness. Some studies 472,473 have shown effectiveness under experimental hospital conditions in Peru and South Africa, and recent advances in dosing and fixture technology and maintenance strategies promise wider use of this highly cost-effective intervention-especially as LED technology eventually replaces conventional lowpressure mercury lamps and fixtures, with the potential for solar and battery power.…”

The HIV-associated tuberculosis epidemic—when will we act?

“…Germicidal ultraviolet upper-room light is also eff ective, but needs electricity and reliable maintenance. 68 Findings from a series of studies in Peru have provided key lessons for interventions to control infection in low-resource settings. 69,70 First, natural ventilation is a low-cost environmental measure for tuberculosis infection control.…”

Transmission and Institutional Infection Control of Tuberculosis

“…During a 4-yr period, for example, Riley estimated an average concentration of infectious quanta of 1 in 11,000 cf (311 m 3 ) and also calculated that this extremely low average concentration was sufficient to explain the rates of transmission to student nurses in hospitals during the prechemotherapy era (Riley 1957;Riley et al 1962). This same approach, using guinea pigs to quantify infectious quanta, has been used to measure the impact of such interventions as ultraviolet air disinfection, electrostatic precipitators, surgical masks on patients, and, most importantly, effective treatment as discussed below (Escombe et al 2009;Dharmadhikari et al 2012Dharmadhikari et al , 2014.…”

“…Because the entire upper room area is available as an air disinfection chamber, room air turnover rates through the upper room can be high, approaching 60 ACH in a recent study, using commercially available inexpensive ceiling fans. Both room testing and modeling suggest that neither fan velocity nor direction are critical factors, although some fan experts favor downward direction in rooms with high ceilings to avoid lower room stagnation (Escombe et al 2009;Zhu et al 2013Zhu et al , 2014. Low vertical air velocity results in longer but fewer passages of particles through the irradiated zone, whereas with higher vertical air velocities, particle exposure per pass is shorter, but passages are more frequent, with similar net exposure.…”