Opening windows may be the best way of preventing transmission of airborne infection / EurekAlert!, 26 February 2007
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"A study of eight hospitals in Peru has shown that opening windows and doors provided ventilation more than double that of mechanically ventilated negative-pressure rooms and 18 times that of rooms with windows and doors closed."

Natural Ventilation for the Prevention of Airborne Contagion
Public Library of Science Medicine 4(2), 27 February 2007
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Escombe AR, Oeser CC, Gilman RH, Navincopa M, Ticona E, et al. (2007) [Sub required]