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
References
[1]
Corbett EL, Watt CJ, Walker N, Maher D, Williams BG, et al. (2003) The growing burden of tuberculosis: Global trends and interactions with the HIV epidemic. Arch Intern Med 163: 1009–1021.
[2]
Valway SE, Greifinger RB, Papania M, Kilburn JO, Woodley C, et al. (1994) Multidrug-resistant tuberculosis in the New York State prison system, 1990–1991. J Infect Dis 170: 151–156.
[3]
Mohle-Boetani JC, Miguelino V, Dewsnup DH, Desmond E, Horowitz E, et al. (2002) Tuberculosis outbreak in a housing unit for human immunodeficiency virus-infected patients in a correctional facility: Transmission risk factors and effective outbreak control. Clin Infect Dis 34: 668–676.
[4]
Dwyer B, Jackson K, Raios K, Sievers A, Wilshire E, et al. (1993) DNA restriction fragment analysis to define an extended cluster of tuberculosis in homeless men and their associates. J Infect Dis 167: 490–494.
[5]
Curtis AB, Ridzon R, Novick LF, Driscoll J, Blair D, et al. (2000) Analysis of transmission patterns in a homeless shelter outbreak. Int J Tuberc Lung Dis 4: 308–313.
[6]
Danis K, Fitzgerald M, Connell J, Conlon M, Murphy PG (2004) Lessons from a pre-season influenza outbreak in a day school. Commun Dis Public Health 7: 179–183.
[7]
Ehrenkranz NJ, Kicklighter JL (1972) Tuberculosis outbreak in a general hospital: Evidence for airborne spread of infection. Ann Intern Med 77(3): 377–382.
[8]
Petrosillo N, Nicastri E, Viale P (2005) Nosocomial pulmonary infections in HIV-positive patients. Curr Opin Pulm Med 11: 231–235.
[9]
Edlin BR, Tokars JI, Grieco MH, Crawford JT, Williams J, et al. (1992) An outbreak of multidrug-resistant tuberculosis among hospitalized patients with the acquired immunodeficiency syndrome. N Engl J Med 326: 1514–1521.
[10]
Ikeda RM, Birkhead GS, DiFerdinando GT Jr, Bornstein DL, Dooley SW, et al. (1995) Nosocomial tuberculosis: An outbreak of a strain resistant to seven drugs. Infect Control Hosp Epidemiol 16: 152–159.
[11]
Jiamjarasrangsi W, Hirunsuthikul N, Kamolratanakul P (2005) Tuberculosis among health care workers at King Chulalongkorn Memorial Hospital, 1988–2002. Int J Tuberc Lung Dis 9: 1253–1258.
[12]
Jensen PA, Lambert LA, Iademarco MF, Ridzon R (2005) Guidelines for preventing the transmission of in health-care settings, 2005. MMWR Recomm Rep 54: 1–141.
[13]
Beggs CB, Noakes CJ, Sleigh PA, Fletcher LA, Siddiqi K (2003) The transmission of tuberculosis in confined spaces: an analytical review of alternative epidemiological models. Int J Tuberc Lung Dis 7: 1015–1026.
[14]
Riley RL, Nardell EA (1989) Clearing the air. The theory and application of ultraviolet air disinfection. Am Rev Respir Dis 139: 1286–1294.
[15]
Granich R, Binkin NJ, Jarvis WR, Simone PM (1999) Guidelines for the prevention of tuberculosis in health care facilities in resource-limited settings. WHO/CDS/TB99.269 ed. Geneva: World Health Organization.
[16]
Menzies R, Schwartzman K, Loo V, Pasztor J (1995) Measuring ventilation of patient care areas in hospitals. Description of a new protocol. Am J Respir Crit Care Med 152: 1992–1999.
[17]
Nardell EA, Keegan J, Cheney SA, Etkind SC (1991) Airborne infection. Theoretical limits of protection achievable by building ventilation. Am Rev Respir Dis 144: 302–306.
[18]
Wells WF (1955) Airborne contagion and air hygiene: An ecological study of droplet infection. Cambridge (Massachusetts): Harvard University Press.
[19]
Kennedy WJ, Bancroft TA (1971) Model-building for prediction in regression based on repeated significance tests. Ann Math Stat 42: 1273–1284.
[20]
Zeger SL, Liang KY, Albert PS (1988) Models for longitudinal data: A generalized estimating equation approach. Biometrics 44: 1049–1060.
[21]
Zheng B (2000) Summarizing the goodness of fit of generalized linear models for longitudinal data. Stat Med 19: 1265–1275.
[22]
SPSS (1999) SPSS User Manual Version 10.0. Chicago: SPSS.
[23]
Menzies D, Fanning A, Yuan L, FitzGerald JM (2000) Hospital ventilation and risk for tuberculous infection in canadian health care workers. Canadian Collaborative Group in Nosocomial Transmission of TB. Ann Intern Med 133: 779–789.
[24]
Fraser VJ, Johnson K, Primack J, Jones M, Medoff G, et al. (1993) Evaluation of rooms with negative pressure ventilation used for respiratory isolation in seven midwestern hospitals. Infect Control Hosp Epidemiol 14: 623–628.
[25]
Pavelchak N, DePersis RP, London M, Stricof R, Oxtoby M, et al. (2000) Identification of factors that disrupt negative air pressurization of respiratory isolation rooms. Infect Control Hosp Epidemiol 21: 191–195.
[26]
Catanzaro A (1982) Nosocomial tuberculosis. Am Rev Respir Dis 125: 559–562.
[27]
Pearson ML, Jereb JA, Frieden TR, Crawford JT, Davis BJ, et al. (1992) Nosocomial transmission of multidrug-resistant . A risk to patients and health care workers. Ann Intern Med 117: 191–196.
[28]
Beck-Sague C, Dooley SW, Hutton MD, Otten J, Breeden A, et al. (1992) Hospital outbreak of multidrug-resistant infections. Factors in transmission to staff and HIV-infected patients. JAMA 268: 1280–1286.
[29]
Coffey CC, Lawrence RB, Campbell DL, Zhuang Z, Calvert CA, et al. (2004) Fitting characteristics of eighteen N95 filtering-facepiece respirators. J Occup Environ Hyg 1: 262–271.
[30]
Biscotto CR, Pedroso ER, Starling CE, Roth VR (2005) Evaluation of N95 respirator use as a tuberculosis control measure in a resource-limited setting. Int J Tuberc Lung Dis 9: 545–549.
[31]
Bonifacio N, Saito M, Gilman RH, Leung F, Cordova Chavez N, et al. (2002) High risk for tuberculosis in hospital physicians, Peru. Emerg Infect Dis 8: 747–748.
[32]
Riley RL, Mills CC, O'Grady F, Sultan LU, Wittstadt F, et al. (1962) Infectiousness of air from a tuberculosis ward. Ultraviolet irradiation of infected air: comparative infectiousness of different patients. Am Rev Respir Dis 85: 511–525.
[33]
Menzies D (1997) Effect of treatment on contagiousness of patients with active pulmonary tuberculosis. Infect Control Hosp Epidemiol 18: 582–586.
[34]
Long R, Zielinski M, Kunimoto D, Manfreda J (2002) The emergency department is a determinant point of contact of tuberculosis patients prior to diagnosis. Int J Tuberc Lung Dis 6: 332–339.
