Media statement
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24 March 2009
Upper room ultraviolet air disinfection shown to reduce transmission of multidrug resistant (MDR) tuberculosis under South African hospital conditions
The SA Medical Research Council (MRC) says that healthcare workers in public health facilities in South Africa, a large proportion of whom may be HIV-Infected, are especially vulnerable to nosocomial transmission of tuberculosis (TB), yet most facilities lack appropriate infection control.
Interim Director of the MRC’s Tuberculosis Epidemiology & Intervention Research Unit, Dr Martie van der Walt states that international guidelines to reduce TB transmission in resource-limited settings are available, but, although based on sound industrial hygiene principles, are generally not supported by scientific data on effectiveness in the intended settings.
“Air disinfection by ventilation (natural and mechanical) and by upper room germicidal ultraviolet fixtures is an important component of transmission control. One limitation to testing air disinfection interventions is the inability to quantitatively culture Mycobacterium tuberculosis (Mtb) from the air under real-life conditions. Because all transmission control interventions have associated costs, proof of efficacy is important in resource-limited conditions,” says Dr Van der Walt.
The MRC together with other partners such as the Mpumalanga Province, CSIR, Centers for Disease Control and Prevention (CDC, USA) and Harvard University (USA) established an Airborne Infectious Research (AIR) facility in Witbank in 2005 to test the effectiveness of air disinfection interventions by quantifying the airborne concentration of infectious Mtb organisms.
Dr Van der Walt mentions that disinfection of upper room air with ultraviolet germicidal irradiation (UVGI) is a well established, safe, and cost-effective technology, but evidence that it is efficacious against transmission of tuberculosis in high burden, resource-limited settings like South Africa is lacking.
The MRC and collaborators from the USA are using the AIR facility to measure the airborne transmission of Multi-drug Resistant (MDR) Mtb using the long-established guinea-pig model for air sampling, and to quantify the effectiveness of UVGI against human generated aerosols containing Mtb.
“Findings thus far suggest that properly engineered upper room UVGI irradiation with good air mixing was highly effective in disinfecting the air from an ordinary hospital room occupied by MDR-TB patients on treatment,” she said.
“Our results are preliminary but very encouraging, and they support the recently published data obtained from similar experiments conducted in Peru. It is however important to note that the dimensions of hospital wards and clinics, occupancy, climatic conditions, UV fixture designs, and UV output in various settings will be different than those in our current study. We plan to replicate the experiments to confirm our findings,” she said. She also mentioned that the installation of the UVGI fixtures requires expert knowledge
Dr van der Walt says, “it is very important that fixture specifications be met in terms of both safety and efficacy, be properly maintained and that fixtures be installed following published recommendations, including the installation of ceiling fans to assure optimal air mixing. Poorly designed or installed UV fixtures can cause temporary eye irritation or not be efficacious for reducing transmission of TB. If fixtures are not properly installed, they may give a false sense of a safe working environment.”
The MRC says that very little data are in general available in support of infection control interventions specifically targeted towards Mtb, and the findings from South Africa and elsewhere help to build the evidence base for UVGI globally. These findings provide the evidence base for policymakers and infection control officers to consider UVGI as a primary mode of air disinfection in appropriate settings to reduce transmission of TB.
South African Guidelines for installation and operating of UVGI can be found at http://www.sahealthinfo.org/tb/guidelines.pdf
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For more information contact: Dr Martie van der Walt – 021 339 8551
More information on Airborne Infectious Research (AIR) facility:
The Airborne Infectious Research (AIR) facility was established in Mpumalanga Province in 2005 as a collaboration of the South African Medical Research Council (MRC), Mpumalanga Province, CSIR, Centers for Disease Control and Prevention (CDC, USA) and Harvard University (USA) to test the effectiveness of air disinfection interventions by quantifying the airborne concentration of infectious Mtb organisms.
Current research funding is from MRC and NIOSH, the US National Institute of Occupational Safety and Health. The facility is part of a regional MDR-TB referral hospital and consists of three 2-bed patient wards from which infectious air is extracted and conveyed to exposure chambers housing sentinel guinea pigs. Guinea pigs are the only method available to quantify infectious Mtb organisms in the air. These laboratory animals are exquisitely susceptible to human Mtb. infection. Interventions that protect guinea pigs from infection are highly likely to protect human healthcare workers, even those who are especially vulnerable due to HIV.
The MRC adheres to strict ethical research on animals as per international standards. |
