Opening windows effective way of preventing transmission of TB
27 February 2007
A study funded by the Wellcome Trust and the Sir Halley Stewart Trust has shown that opening windows can be more effective than using mechanical ventilation at reducing the risk of transmission of airborne diseases such as tuberculosis (TB).
The spread of airborne infections in institutional settings such as hospitals, waiting rooms, prisons and homeless shelters is an important public health problem. This is especially true in resource-poor settings, where the prevalence of TB is highest, and where preventive measures such as negative-pressure isolation rooms are hardest to implement.
A study published today in the journal 'PLoS Medicine', and carried out by researchers from the Department of Infectious Diseases and Immunity and the Wellcome Trust Centre for Clinical Tropical Medicine, Imperial College London, is the first to investigate the role of natural ventilation by opening windows and doors for preventing the transmission of airborne infection. This simple and low-cost measure is recommended by the WHO for preventing TB transmission in healthcare settings, but until now there have been no studies to support these guidelines.
The researchers, led by Dr Rod Escombe from Imperial College London, studied eight hospitals in Lima (Peru) and measured natural ventilation in 70 different rooms where infectious patients are likely to be found, including: respiratory isolation rooms; TB wards; respiratory wards; general medical wards; outpatient consulting rooms; waiting rooms; and emergency departments. They compared these with 12 modern mechanically ventilated, negative-pressure respiratory isolation rooms.
The study found that natural ventilation when windows and doors were opened was more than double that of mechanically ventilated, negative-pressure rooms functioning at the high rates recommended by guidelines, and 18 times that of rooms with windows and doors closed. Even at the lowest wind speeds, natural ventilation exceeded mechanical ventilation.
"We were surprised by how effective simply opening windows and doors was at generating high rates of ventilation, which would theoretically reduce the risk of transmission," says Dr Escombe. "Using an airborne infection model to predict the effect of natural ventilation on TB transmission, we estimated that in mechanically-ventilated rooms, 39 per cent of susceptible individuals would become infected following 24 hours of exposure to untreated TB patients. This compared with 33 per cent in modern and 11 per cent in pre-1950 naturally ventilated facilities with windows and doors open."
Facilities built more than 50 years ago, characterised by large windows and high ceilings, had greater ventilation than modern naturally ventilated rooms. Some of these older facilities had been built especially for TB patients, along the design principles of TB sanatoria when fresh air was part of the treatment for TB in the pre-antibiotic era.
"We concluded that opening windows and doors provides high rates of ventilation and may therefore provide the most effective protection against airborne infection in low resource settings," says Dr Escombe. "Old-fashioned clinical areas with high ceilings and large windows provided the greatest protection. Mechanically ventilated negative-pressure isolation rooms are very expensive to install and maintain, and are limited to certain high-risk areas such as TB isolation rooms. In contrast, natural ventilation is a low-cost, low-tech intervention that can be applied in many different areas, including waiting rooms, out-patient clinics and emergency departments, where many infectious patients are found. While not suited to cold climates, natural ventilation offers an important infection control measure in the tropics, where the greatest burden of TB is found."
Contact
Craig Brierley
Media Officer
Wellcome Trust
T +44 (0)20 7611 7329
E
c.brierley@wellcome.ac.uk
Dr Rod Escombe
T Peru contact: +51 1 9229 9097; UK contact:+44 (0)7941942189
E
rod.escombe@imperial.ac.uk
Notes for editors
1. Escombe AR et al. Natural ventilation for the prevention of airborne contagion. PLoS Med 2007;4(2):e68.
2. Press preview copy of the paper [PDF 692KB]
3. Image to accompany the article
4. The Wellcome Trust is the largest independent charity in the UK and the second largest medical research charity in the world. It funds innovative biomedical research, in the UK and internationally, spending around £500 million each year to support the brightest scientists with the best ideas. The Wellcome Trust supports public debate about biomedical research and its impact on health and wellbeing.
5. The Sir Halley Stewart Trust has a Christian basis and is concerned with the development of body, mind and spirit, a just environment and international goodwill. To this end, it supports projects in religious, social, educational and medical fields. The Sir Halley Stewart Trust aims to promote and assist innovative research activities or pioneering developments with a view to making such work self-supporting. It emphasises prevention rather than alleviation of human suffering.
6. Imperial College London is consistently rated in the top three UK university institutions. It is a world-leading science-based university whose reputation for excellence in teaching and research attracts students (11 000) and staff (6000) of the highest international quality. Innovative research at Imperial explores the interface between science, medicine, engineering and management, and delivers practical solutions that enhance the quality of life and the environment, underpinned by a dynamic enterprise culture.