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Since the 1990s, improvements in ventilation techniques and isolation procedures have been widely credited with the decline in nosocomial transmission of tuberculosis and other airborne diseases. Little effort, however, has been made to study the risk of isolation patients acquiring secondary infections from contaminated air migrating into negatively pressurized isolation rooms from adjacent spaces. As a result, an actual hospital was used to observe the transport of aerosol from a nursing station and general patient room to a nearby airborne infectious isolation room (AIIR). Aerosols ≤3.0μm (viruses and most airborne bacteria) were found to be capable of migrating 14.5m from a general patient room to an AIIR anteroom entrance in 3.0μm to the entrance of the general patient room (4.5m).

Approximately half of the nosocomial aspergillosis outbreaks in hospitals have been associated with renovation activities. When disturbed, spores encapsulated in building materials can be aerosoliz...

Placing an Airborne Infectious Isolation Room (AIIR) into a negative pressure has proven to protect the hospital from fatal pathogens such as tuberculosis and other airborne diseases. However, this pressurization strategy could increase the risk of isolation patients acquiring secondary infections from contaminated air drawn in from adjacent spaces. As a result, an actual hospital was used to observe the transport of aerosol from a general patient room and nurse station to a nearby airborne infectious isolation room. Two experimental studies were designed to analyze the performance of a negative anteroom. Aerosols ≤3.0 μm (viruses and most airborne bacteria) were found to be capable of migrating out of a general patient room to the vicinity of the nurse station. Concentrations of aerosols within the anteroom and isolation room increased from ambient when injected at the nurse station, indicating the capability of aerosols to migrate into the isolation room upon negative pressurization. Subsequently, a series of CFD models, validated by the experiments, were developed to simulate a positively pressurized anteroom. An anteroom with a positive pressure was shown to effectively terminate cross-contamination between the corridor and the isolation room in both directions.

Certain pathogens are transmitted through air by respiratory droplets that desiccate shortly after emission and form droplet nuclei (Nicas et al. 2005). Droplet nuclei are sufficiently small (

Most studies on the transmission of infectious airborne disease have focused on patient room air changes per hour (ACH) and how ACH provides pathogen dilution and removal. The logical but mostly unproven premise is that greater air change rates reduce the concentration of infectious particles and thus, the probability of airborne disease transmission. Recently, a growing body of research suggests pathways between pathogenic source (patient) and control (exhaust) may be the dominant environmental factor. While increases in airborne disease transmission have been associated with ventilation rates below 2 ACH, comparatively less data are available to quantify the benefits of higher air change rates in clinical spaces. As a result, a series of tests were conducted in an actual hospital to observe the containment and removal of respirable aerosols (0.5-10 µm) with respect to ventilation rate and directional airflow in a general patient room, and, an airborne infectious isolation room. Higher ventilation rates were not found to be proportionately effective in reducing aerosol concentrations. Specifically, increasing mechanical ventilation from 2.5 to 5.5 ACH reduced aerosol concentrations only 30% on average. However, particle concentrations were more than 40% higher in pathways between the source and exhaust as was the suspension and migration of larger particles (3-10 µm) throughout the patient room(s). Computational analyses were used to validate the experimental results, and, to further quantify the effect of ventilation rate on exhaust and deposition removal in patient rooms as well as other particle transport phenomena.