Natural Ventilation for the Prevention of Airborne Contagion

Abstract

BackgroundInstitutional 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 FindingsThe 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.ConclusionsOpening 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.

The HIV-associated tuberculosis epidemic—when will we act?

“…68 Findings from a series of studies in Peru have provided key lessons for interventions to control infection in low-resource settings. 69,70 First, natural ventilation is a low-cost environmental measure for tuberculosis infection control. Maximum natural ventilation can be achieved with open windows and doors, enlarged or additional windows, open skylights for cross-ventilation, and rebuilding of waiting rooms in the open air.…”

“…Maximum natural ventilation can be achieved with open windows and doors, enlarged or additional windows, open skylights for cross-ventilation, and rebuilding of waiting rooms in the open air. 69 These measures provide much higher airfl ow than do costly mechanical ventilation systems, many of which function well below recom mended levels because of poor maintenance. Second, unrecognised or inadequately treated MDR tuberculosis can be a key source of nosocomial transmission, which further emphasises the importance of environmental control measures in crowded health-care settings, and the importance of rapid testing for drug susceptibility to allow eff ective treatment to be started promptly.…”

Influenza B virus outbreak at a religious residential school for boys in Northern Bangladesh, 2011

“…Changes in student behaviour during Ramadan and rainfall to stay indoors likely facilitated person‐to‐person transmission 8. The small windows limiting natural cross‐ventilation9 and restricted sunlight entry preventing viral inactivation by ultraviolet solar irradiation further increased scope of airborne transmission 10. Moreover, rainfall preceding outbreak onset likely increased environmental viral circulation 11.…”

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“…1 There is overwhelming evidence to suggest that the risk of TB transmission is high in prisons, schools, home shelters, other congregate settings and health care facilities. 2,3 Good ventilation, either natural or mechanical, seems to be the optimal solution to reduce the risk of infection in these settings. 3,4 In tropical countries the climate, coupled with high population density, also favours longer survival of the bacilli.…”

“…2,3 Good ventilation, either natural or mechanical, seems to be the optimal solution to reduce the risk of infection in these settings. 3,4 In tropical countries the climate, coupled with high population density, also favours longer survival of the bacilli. 5,6 The United Nations has incorporated TB elimination as a part of its sustainable development goals (SDGs) for 2030.…”