Ventilation

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To Prevent Transmission Of TB Just Opoen Windows

Main Category: Infectious Diseases / Bacteria / Viruses News

Article 28 Feb 2007 - 14:00 PST

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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 in the freely available 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% of susceptible individuals would

become infected following 24 hours of exposure to untreated TB

patients. This compared with 33% in modern and 11% in pre-1950

naturally ventilated facilities with windows and doors open. "

 

Facilities built more than 50 years ago, characterized 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. Whilst not

suited to cold climates, natural ventilation offers an important

infection control measure in the tropics, where the greatest burden

of TB is found. "

 

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Contact: Craig Brierley

Wellcome Trust