Affiliations: Toronto, ON, Canada,
Prince of Wales Hospital, Hong Kong
Correspondence to: Joseph A. Fisher, MD, Toronto General Hospital, 7EN-242, 200 Elizabeth St, Toronto, ON, Canada M5G 2C4; e-mail: firstname.lastname@example.org
Hui et al1provide a much needed reminder to the medical community that the very oxygen mask that is used to relieve the hypoxia may contribute to the wide dispersal of infected aerosolized particles, and thereby increases the risk of transmission of airborne infection to health-care workers. However, I believe the authors do a disservice by unequivocally declaring that their data allows the demarcation of “a zone of potential aerosol infection with an extra margin of safety.” They would do well to temper this conclusion based on theoretical arguments from a mechanical model with those based on published in vivo observations2 in humans that clearly demonstrate aerosolized particles traveling, not 30 or 40, but hundreds of centimeters.
The authors conclude that potential infectious patients “should, ideally, be managed in a single, isolation room, under negative pressure… ” This type of conclusion simply does not follow from the type of study performed. Furthermore, it is hard to see how managing a contagious patient in a negative-pressure room would provide any protection to a health-care worker. On the other hand, preventing the patients from spraying infectious particles on health-care workers while being administered oxygen, as we have advocated,3–4 would provide protection to other patients and health-care workers alike.
The author is the co-developer of masks described in references 3and 4 that have been licensed to Viasys Healthcare Inc.
The authors have no conflicts of interest to declare.
We appreciate the comments by Dr. Fisher on our study,1which showed a smoke particle dispersion distance of approximately 0.4 m during application of 4 L/min of oxygen via a simple mask to a human patient simulator. As we pointed out in our article, our human lung model simply reflected a baseline estimate of the distance traveled by any potentially infectious aerosols while the patient was breathing at rest with a respiratory rate of 12 breaths/min. With appropriate references,2–3 we have already stressed the importance of full personal protective equipment as an effective infection control measure in protecting health-care workers against severe acute respiratory syndrome.1
We are well aware of the possibility that viral infection such as severe acute respiratory syndrome has the potential of spreading by an airborne route, and indeed our institution has made a significant contribution to the literature on this issue.4–5 It is important for clinicians involved in the management of infectious diseases to understand that environmental factors such as medical ward airflow and ventilation may play a significant role in the aerosol transmission of infection in health-care premises.6In addition to full personal protective equipment and good personal hygiene, the World Health Organization and the Centers for Disease Control and Prevention have recommended in influenza pandemic plans enhanced infection control precautions in health-care facilities, including placing patients with suspected and confirmed H5N1 influenza in negative-pressure isolation rooms with 6 to 12 air exchanges per hour (if available) due to the high lethality of the disease and uncertainty about the mode of human to human transmission.7–8 The negative-pressure room will reduce the spread of airborne contamination between rooms, and a recent study9 has shown that the air exchange rate and airflow patterns are important factors in the control of airborne virus infection, and good ventilation arrangement may enhance the safety of staff when performing medical treatments within isolation rooms.
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