Rationale: Transmission of multi and extensively drug resistant (MDR and XDR) TB in congregate settings threatens global TB control. Recommended engineering interventions to reduce transmission include high rates of natural/mechanical ventilation and use of upper room UVGI with good air mixing, but with very little direct evidence of efficacy. We sought to directly measure the efficacy of upper room UVGI in reducing TB transmission on an actual MDR-TB ward with low and high humidity. High humidity purportedly negatively affects UVGI efficacy. Methods: For each 2-3 month study, a series of 6 consenting MDR/XDR patients simultaneously occupied the Airborne Infections Research facility ward at the Mpumalanga Provincial MDR Referral Hospital in Witbank, South Africa. Patients were selected for features associated with increased transmissibility: smear (+) sputum, coughing, lung cavitation, and recent initiation of standardized treatment, and remained on the ward 2 weeks before being replaced. Patient rooms, hallways, and a common area were equipped with UVGI fixtures producing high levels of upper room UVGI with safe exposure levels in the lower, occupied portion of the room. Slow paddle fans assured good air mixing in the rooms. A mechanical ventilation system exhausted all ward air to two identical exposure chambers each containing 90 tuberculin skin test (TST) negative, pathogen-free laboratory guinea pigs. Guinea pigs are highly susceptible to TB and serve as living sentinel air samplers for infectious airborne TB droplet nuclei. After a baseline TST, monthly TST conversions represented the fraction of infected animals in each chamber. Experimental animals only breathed UV irradiated ward air on even days whereas control animals only breathed unirradiated ward air on odd days. Low (55 - 65%) and high (70 - 80%) humidity were achieved using a humidifier. Upper room UVGI efficacy was determined by comparing the proportion of infected animals in each chamber and using survival analysis. Results: Under low humidity, 0 experimental guinea pigs versus 9 control guinea pigs became infected (100% efficacy for UV). In a second low humidity study, 15 experimental guinea pigs versus 48 control guinea pigs became infected (69% efficacy for UV). Combined survival analysis for differences in infections between the 2 arms was highly significant (p<0.0005) with a hazard ratio of 4.9 (95% CI 2.8-8.6) for infection breathing unirradiated air. A third study with high humidity is currently in progress. Conclusions: Upper room UVGI with low humidity very effectively reduces airborne TB transmission under real world conditions in Africa.
We take your privacy seriously. You can review and change the way we collect information below.
These cookies allow us to count visits and traffic sources so we can measure and improve the performance of our site. They help us to know which pages are the most and least popular and see how visitors move around the site. All information these cookies collect is aggregated and therefore anonymous. If you do not allow these cookies we will not know when you have visited our site, and will not be able to monitor its performance.
Cookies used to make website functionality more relevant to you. These cookies perform functions like remembering presentation options or choices and, in some cases, delivery of web content that based on self-identified area of interests.
Cookies used to track the effectiveness of CDC public health campaigns through clickthrough data.
Cookies used to enable you to share pages and content that you find interesting on CDC.gov through third party social networking and other websites. These cookies may also be used for advertising purposes by these third parties.