What is the evidence that negative pressure rooms avoid nosocomial spread of SARS-CoV2?Posted on by
There is currently no published evidence that negative pressure rooms avoid nosocomial spread of SARS-CoV-2. Recent guideline recommendations to use negative pressure rooms are based on basic science and theoretical principles as referenced in the CDC’s Guidelines for Environmental Control in Health-Care Facilities.
I. Review of Basics from the CDC’s Guidelines for Environmental Control in Health-Care Facilities (1):
- Positive and negative pressures refer to the differential between two adjacent spaces (ex. operating rooms and hallways). Negative pressure rooms are created by a differential that allows airflow into the room, but not out of the room. Positive pressure rooms maintain a higher pressure in the room, allowing airflow out but not in. These principles have been shown to be effective at directing general airflow direction.
- Negative pressure rooms are generally used when you have an airborne infectious source in a room and want to keep the infectious particles within the room.
- Positive pressure rooms are generally used when you have an immunocompromised individual in the room and don’t want anything getting in that may compromise them.
- Other ventilation issues need to be addressed, including fan locations to determine clean-to-dirty airflow and type of filters in place for air supplied into the room and out of the room in negative pressure rooms. Many negative pressure rooms don’t have a filter on the outgoing air and simply place the exhaust so as to prevent re-entry to the building.
II. Evidence that negative pressure rooms reduce nosocomial infections is lacking:
- The CDC’s 1993 guidelines on prevention of nosocomial M. tuberculosis infections required the use of negative pressure rooms based on theoretical benefit with no studies to support efficacy (3).
- A 2000 study assessing efficacy and disruption of negative pressure rooms states, “there is a general consensus on the usefulness and theoretical function of [respiratory isolation rooms], including the need for directional airflow…” (4) while citing the above CDC guidelines and other regulatory bodies.
A PubMed search using a combination of keywords such as negative pressure, airborne, nosocomial, respiratory, and effectiveness did not yield any reviews or publications that directly tested the hypothesis that negative pressure rooms reduce the incidence of nosocomial infections. Several cited sources such as, Guidelines for design and construction of hospital and outpatient facilities by the American Society for Healthcare Engineering of the American Hospital Association, or the Ventilation for health care facilities guidelines by the American Society of Heating, Refrigerating and Air-Conditioning Engineers to support their assertions that negative pressure rooms are needed in airborne infection prevention.
III. What does this mean in the context of SARS-COV2?
- A literature search on PubMed using the key words COVID-19, SARS-CoV-2, SARS, and negative pressure, yielded no studies specifically looking at the efficacy of negative pressure rooms at preventing SARS-CoV-2 infections.
- One study from 2006 looked at a single patient with Severe acute respiratory syndrome (SARS) in a negative pressure room and aerosol generation via a nebulizer. They then sampled the air several times and all air samples tested negative for SARS-CoV, however; there are other factors at play such as air filters used, patient factors, disease course, etc. (2)
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- Guidelines for Environmental Infection Control in health-Care Facilities [Internet]. Center for Disease Control and Prevention. 2020 [cited 2020 May 19]. Available from: https://www.cdc.gov/infectioncontrol/guidelines/environmental/background/air.html
- Tsai Y-H, Wan G-H, Wu Y-K, Tsao K-C. Airborne Severe Acute Respiratory Syndrome Coronavirus Concentrations in a Negative-Pressure Isolation Room. Infection Control & Hospital Epidemiology. 2006 May;27(5):523–5.
- Bozzi C, Burwen D, Dooley S, Simone P, Beck-Sague C, Bolyard E, et al. Publication of Draft Guidelines for Preventing the Transmission of Tuberculosis in Health-Care Facilities, Second Edition. JAMA: The Journal of the American Medical Association. 1993 Nov 10;270(18):2164.
- Pavelchak N, DePersis RP, London M, Stricof R, Oxtoby M, DiFerdinando G, et al. Identification of Factors That Disrupt Negative Air Pressurization of Respiratory Isolation Rooms. Infection Control & Hospital Epidemiology. 2000 Mar;21(3):191–5.
- The Facility Guidelines Institute; Guidelines for design and construction of hospital and outpatient facilities.2014 ed. American Society for Healthcare Engineering of the American Hospital Association, Chicago (IL)2009: 422-427
- ASHRAE Standard 170-2013; Ventilation for health care facilities.American Society of Heating, Refrigerating and Air-Conditioning Engineers, Inc., Atlanta (GA)2013
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