03 January 2008

Open windows prevent TB

A study 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.

A study 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 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 World Health Organization (WHO) for preventing TB transmission in healthcare settings, but until now there have been no studies to support these guidelines.

Testing natural ventilation
The researchers, led by Dr Rod Escombe 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 were 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 percent of susceptible individuals would become infected following 24 hours of exposure to untreated TB patients. This compared with 33 percent in modern and 11 percent 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.

"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." – (EurekAlert!)

Source: PLoS Medicine

Read more:
Open windows beat germs
TB Centre

January 2008


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