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Natural ventilation for the prevention of airborne contagion.

Escombe AR, Oeser CC, Gilman RH, Navincopa M, Ticona E, Pan W, Martínez C, Chacaltana J, Rodríguez R, Moore DA, Friedland JS, Evans CA - PLoS Med. (2007)

Bottom Line: These rooms were compared with 12 mechanically ventilated negative-pressure respiratory isolation rooms built post-2000.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).In settings where respiratory isolation is difficult and climate permits, windows and doors should be opened to reduce the risk of airborne contagion.

View Article: PubMed Central - PubMed

Affiliation: Department of Infectious Diseases & Immunity, Imperial College London, London, United Kingdom. rod.escombe@imperial.ac.uk

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 "old-fashioned" 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 Wells-Riley 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.

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Ventilation and Protection against Airborne TB Transmission in Old-Fashioned Compared with Modern RoomsVentilation and protection against airborne infection is shown for pre-1950 versus modern (1970–1990) naturally ventilated facilities versus mechanically ventilated negative-pressure respiratory isolation rooms. The triplet of bars on the left represents ACH in old-fashioned, high-ceilinged, pre-1950 naturally ventilated clinical areas (n = 22; 201 experiments), versus modern naturally ventilated facilities (n = 42; 125 experiments), versus mechanically ventilated negative-pressure facilities (n = 12). The left-centre triplet of bars represents the same comparison for absolute ventilation (m3/h/100); the right-centre triplet of bars represents that for absolute ventilation per person (m3/h/100); and the triplet of bars on the right that for the estimated risk of airborne TB transmission (percentage of susceptible persons infected), for 24-h exposure to infectious TB patients [17]. Data are shown for 64 naturally ventilated rooms with windows and doors fully open (the remaining six naturally ventilated rooms had windows that could not be fully opened).
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pmed-0040068-g003: Ventilation and Protection against Airborne TB Transmission in Old-Fashioned Compared with Modern RoomsVentilation and protection against airborne infection is shown for pre-1950 versus modern (1970–1990) naturally ventilated facilities versus mechanically ventilated negative-pressure respiratory isolation rooms. The triplet of bars on the left represents ACH in old-fashioned, high-ceilinged, pre-1950 naturally ventilated clinical areas (n = 22; 201 experiments), versus modern naturally ventilated facilities (n = 42; 125 experiments), versus mechanically ventilated negative-pressure facilities (n = 12). The left-centre triplet of bars represents the same comparison for absolute ventilation (m3/h/100); the right-centre triplet of bars represents that for absolute ventilation per person (m3/h/100); and the triplet of bars on the right that for the estimated risk of airborne TB transmission (percentage of susceptible persons infected), for 24-h exposure to infectious TB patients [17]. Data are shown for 64 naturally ventilated rooms with windows and doors fully open (the remaining six naturally ventilated rooms had windows that could not be fully opened).

Mentions: Old-fashioned facilities built pre-1950 had greater natural ventilation than more modern rooms built 1970–1990. With windows and doors fully open, the median absolute ventilation was 3,769 versus 1,174 m3/hour, the median absolute ventilation per person was 1,557 m3/h versus 461 m3/h, and the ACH were 40 versus 17, respectively (all p < 0.001; Figure 3; Table 2). Compared with the modern naturally ventilated facilities, these pre-1950 facilities were larger (85 m3 versus 60 m3), with higher ceilings (4.2 m versus 3.0 m), larger windows (area 6.6 m2 versus 3.4 m2; window area to room volume ratio 0.1 versus 0.05) and were more likely to have windows on opposite walls allowing through-flow of air (56% versus 19% of rooms) (all p < 0.05). Importantly for calculations of airborne infection risk, patient crowding was similar in old-fashioned and modern wards (floor area/patient 9.2 versus 9.3 m2; p = 0.5). Floor area per patient tended to be greater in modern mechanically ventilated isolation rooms than in naturally ventilated rooms, but this difference was not significant (median floor area in mechanically ventilated rooms 11 m2; p = 0.1).


Natural ventilation for the prevention of airborne contagion.

Escombe AR, Oeser CC, Gilman RH, Navincopa M, Ticona E, Pan W, Martínez C, Chacaltana J, Rodríguez R, Moore DA, Friedland JS, Evans CA - PLoS Med. (2007)

Ventilation and Protection against Airborne TB Transmission in Old-Fashioned Compared with Modern RoomsVentilation and protection against airborne infection is shown for pre-1950 versus modern (1970–1990) naturally ventilated facilities versus mechanically ventilated negative-pressure respiratory isolation rooms. The triplet of bars on the left represents ACH in old-fashioned, high-ceilinged, pre-1950 naturally ventilated clinical areas (n = 22; 201 experiments), versus modern naturally ventilated facilities (n = 42; 125 experiments), versus mechanically ventilated negative-pressure facilities (n = 12). The left-centre triplet of bars represents the same comparison for absolute ventilation (m3/h/100); the right-centre triplet of bars represents that for absolute ventilation per person (m3/h/100); and the triplet of bars on the right that for the estimated risk of airborne TB transmission (percentage of susceptible persons infected), for 24-h exposure to infectious TB patients [17]. Data are shown for 64 naturally ventilated rooms with windows and doors fully open (the remaining six naturally ventilated rooms had windows that could not be fully opened).
© Copyright Policy
Related In: Results  -  Collection

Show All Figures
getmorefigures.php?uid=PMC1808096&req=5

pmed-0040068-g003: Ventilation and Protection against Airborne TB Transmission in Old-Fashioned Compared with Modern RoomsVentilation and protection against airborne infection is shown for pre-1950 versus modern (1970–1990) naturally ventilated facilities versus mechanically ventilated negative-pressure respiratory isolation rooms. The triplet of bars on the left represents ACH in old-fashioned, high-ceilinged, pre-1950 naturally ventilated clinical areas (n = 22; 201 experiments), versus modern naturally ventilated facilities (n = 42; 125 experiments), versus mechanically ventilated negative-pressure facilities (n = 12). The left-centre triplet of bars represents the same comparison for absolute ventilation (m3/h/100); the right-centre triplet of bars represents that for absolute ventilation per person (m3/h/100); and the triplet of bars on the right that for the estimated risk of airborne TB transmission (percentage of susceptible persons infected), for 24-h exposure to infectious TB patients [17]. Data are shown for 64 naturally ventilated rooms with windows and doors fully open (the remaining six naturally ventilated rooms had windows that could not be fully opened).
Mentions: Old-fashioned facilities built pre-1950 had greater natural ventilation than more modern rooms built 1970–1990. With windows and doors fully open, the median absolute ventilation was 3,769 versus 1,174 m3/hour, the median absolute ventilation per person was 1,557 m3/h versus 461 m3/h, and the ACH were 40 versus 17, respectively (all p < 0.001; Figure 3; Table 2). Compared with the modern naturally ventilated facilities, these pre-1950 facilities were larger (85 m3 versus 60 m3), with higher ceilings (4.2 m versus 3.0 m), larger windows (area 6.6 m2 versus 3.4 m2; window area to room volume ratio 0.1 versus 0.05) and were more likely to have windows on opposite walls allowing through-flow of air (56% versus 19% of rooms) (all p < 0.05). Importantly for calculations of airborne infection risk, patient crowding was similar in old-fashioned and modern wards (floor area/patient 9.2 versus 9.3 m2; p = 0.5). Floor area per patient tended to be greater in modern mechanically ventilated isolation rooms than in naturally ventilated rooms, but this difference was not significant (median floor area in mechanically ventilated rooms 11 m2; p = 0.1).

Bottom Line: These rooms were compared with 12 mechanically ventilated negative-pressure respiratory isolation rooms built post-2000.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).In settings where respiratory isolation is difficult and climate permits, windows and doors should be opened to reduce the risk of airborne contagion.

View Article: PubMed Central - PubMed

Affiliation: Department of Infectious Diseases & Immunity, Imperial College London, London, United Kingdom. rod.escombe@imperial.ac.uk

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 "old-fashioned" 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 Wells-Riley 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.

Show MeSH
Related in: MedlinePlus