Natural ventilation for the prevention of airborne contagion
File(s)
Author(s)
Type
Journal Article
Abstract
Background
Institutional transmission of airborne infections such as tuberculosis (TB) is an important
public health problem, especially in resource-limited settings where protective measures such
as negative-pressure isolation rooms are difficult to implement. Natural ventilation may offer a
low-cost alternative. Our objective was to investigate the rates, determinants, and effects of
natural ventilation in health care settings.
Methods and Findings
The study was carried out in eight hospitals in Lima, Peru; five were hospitals of ‘‘oldfashioned’’
design built pre-1950, and three of ‘‘modern’’ design, built 1970–1990. In these
hospitals 70 naturally ventilated clinical rooms where infectious patients are likely to be
encountered were studied. These included respiratory isolation rooms, TB wards, respiratory
wards, general medical wards, outpatient consulting rooms, waiting rooms, and emergency
departments. These rooms were compared with 12 mechanically ventilated negative-pressure
respiratory isolation rooms built post-2000. Ventilation was measured using a carbon dioxide
tracer gas technique in 368 experiments. Architectural and environmental variables were
measured. For each experiment, infection risk was estimated for TB exposure using the WellsRiley
model of airborne infection. We found that opening windows and doors provided median
ventilation of 28 air changes/hour (ACH), more than double that of mechanically ventilated
negative-pressure rooms ventilated at the 12 ACH recommended for high-risk areas, and 18
times that with windows and doors closed (p , 0.001). Facilities built more than 50 years ago,
characterised by large windows and high ceilings, had greater ventilation than modern
naturally ventilated rooms (40 versus 17 ACH; p , 0.001). Even within the lowest quartile of
wind speeds, natural ventilation exceeded mechanical (p , 0.001). The Wells-Riley airborne
infection model predicted that in mechanically ventilated rooms 39% of susceptible individuals
would become infected following 24 h of exposure to untreated TB patients of infectiousness
characterised in a well-documented outbreak. This infection rate compared with 33% in
modern and 11% in pre-1950 naturally ventilated facilities with windows and doors open.
Conclusions
Opening windows and doors maximises natural ventilation so that the risk of airborne
contagion is much lower than with costly, maintenance-requiring mechanical ventilation
systems. Old-fashioned clinical areas with high ceilings and large windows provide greatest
protection. Natural ventilation costs little and is maintenance free, and is particularly suited to
limited-resource settings and tropical climates, where the burden of TB and institutional TB
transmission is highest. In settings where respiratory isolation is difficult and climate permits,
windows and doors should be opened to reduce the risk of airborne contagion.
Institutional transmission of airborne infections such as tuberculosis (TB) is an important
public health problem, especially in resource-limited settings where protective measures such
as negative-pressure isolation rooms are difficult to implement. Natural ventilation may offer a
low-cost alternative. Our objective was to investigate the rates, determinants, and effects of
natural ventilation in health care settings.
Methods and Findings
The study was carried out in eight hospitals in Lima, Peru; five were hospitals of ‘‘oldfashioned’’
design built pre-1950, and three of ‘‘modern’’ design, built 1970–1990. In these
hospitals 70 naturally ventilated clinical rooms where infectious patients are likely to be
encountered were studied. These included respiratory isolation rooms, TB wards, respiratory
wards, general medical wards, outpatient consulting rooms, waiting rooms, and emergency
departments. These rooms were compared with 12 mechanically ventilated negative-pressure
respiratory isolation rooms built post-2000. Ventilation was measured using a carbon dioxide
tracer gas technique in 368 experiments. Architectural and environmental variables were
measured. For each experiment, infection risk was estimated for TB exposure using the WellsRiley
model of airborne infection. We found that opening windows and doors provided median
ventilation of 28 air changes/hour (ACH), more than double that of mechanically ventilated
negative-pressure rooms ventilated at the 12 ACH recommended for high-risk areas, and 18
times that with windows and doors closed (p , 0.001). Facilities built more than 50 years ago,
characterised by large windows and high ceilings, had greater ventilation than modern
naturally ventilated rooms (40 versus 17 ACH; p , 0.001). Even within the lowest quartile of
wind speeds, natural ventilation exceeded mechanical (p , 0.001). The Wells-Riley airborne
infection model predicted that in mechanically ventilated rooms 39% of susceptible individuals
would become infected following 24 h of exposure to untreated TB patients of infectiousness
characterised in a well-documented outbreak. This infection rate compared with 33% in
modern and 11% in pre-1950 naturally ventilated facilities with windows and doors open.
Conclusions
Opening windows and doors maximises natural ventilation so that the risk of airborne
contagion is much lower than with costly, maintenance-requiring mechanical ventilation
systems. Old-fashioned clinical areas with high ceilings and large windows provide greatest
protection. Natural ventilation costs little and is maintenance free, and is particularly suited to
limited-resource settings and tropical climates, where the burden of TB and institutional TB
transmission is highest. In settings where respiratory isolation is difficult and climate permits,
windows and doors should be opened to reduce the risk of airborne contagion.
Date Issued
2007-02-27
Date Acceptance
2007-01-04
Citation
PLOS Medicine, 2007, 4 (2), pp.309-317
ISSN
1549-1277
Publisher
Public Library of Science
Start Page
309
End Page
317
Journal / Book Title
PLOS Medicine
Volume
4
Issue
2
Copyright Statement
© 2007 Escombe et al.
This is an open-access article
distributed under the terms of the
Creative Commons Attribution
License, which permits unrestricted
use, distribution, and reproduction
in any medium, provided the
original author and source are
credited.
This is an open-access article
distributed under the terms of the
Creative Commons Attribution
License, which permits unrestricted
use, distribution, and reproduction
in any medium, provided the
original author and source are
credited.
License URL
Subjects
Science & Technology
Life Sciences & Biomedicine
Medicine, General & Internal
General & Internal Medicine
MEDICINE, GENERAL & INTERNAL
HEALTH-CARE WORKERS
RESISTANT MYCOBACTERIUM-TUBERCULOSIS
NOSOCOMIAL TUBERCULOSIS
RESPIRATORY ISOLATION
INFECTED PATIENTS
LONGITUDINAL DATA
OUTBREAK
TRANSMISSION
MODELS
RISK
Publication Status
Published
Article Number
e68