Impact of air-handling system exhaust failure on dissemination pattern of simulant pathogen particles in a clinical biocontainment unit.

Biocontainment units (BCUs) are facilities used to care for patients with highly infectious diseases. However, there is limited guidance on BCU protocols and design. This study presents the first investigation of how HVAC (heating, ventilation, air-conditioning) operating conditions influence the dissemination of fluorescent tracer particles released in a BCU. Test conditions included normal HVAC operation and exhaust failure resulting in loss of negative pressure. A suspension of optical brightener powder and water was nebulized to produce fluorescent particles simulating droplet nuclei (0.5-5 µm). Airborne particle number concentrations were monitored by Instantaneous Biological Analyzers and Collectors (FLIR Systems). During normal HVAC operation, fluorescent tracer particles were contained in the isolation room (average concentration = 1 × 104 ± 3 × 103 /Lair ). Under exhaust failure, the automated HVAC system maximizes airflow into areas adjacent to isolation rooms to attempt to maintain negative pressure differential. However, 6% of the fluorescent particles were transported through cracks around doors/door handles out of the isolation room via airflow alone and not by movement of personnel or doors. Overall, this study provides a systematic method for evaluating capabilities to contain aerosolized particles during various HVAC scenarios. Recommendations are provided to improve situation-specific BCU safety.

Identifying Potential Provider and Environmental Contamination on a Clinical Biocontainment Unit Using Aerosolized Pathogen Simulants.

The Johns Hopkins Hospital created a biocontainment unit (BCU) to care for patients with highly infectious diseases while assuring healthcare worker safety. Research to date for BCU protocols and practices are based on case reports and lessons learned from patient care and exercises. This study seeks to be the first to explore the influences of healthcare worker movement and personal protective equipment (PPE) doffing on the transport of simulant pathogen particles in a BCU. A cough device released 1 µm fluorescent polystyrene beads (PSLs) in the patient room. PSL transport was then examined under 2 scenarios: (1) PSL release only, no healthcare workers; and (2) PSL release during 5-minute simulated activity by healthcare workers. Airborne PSL concentrations were quantified every second for 30 minutes per scenario by 7 optical particle sensors located throughout the BCU. PSLs were not detected in the donning room at any time nor in the doffing room during the first test scenario where no healthcare worker was present. The main difference detected between the tested scenarios was the presence of PSLs in the doffing room when healthcare workers were removing PPE, potentially due to re-aerosolization of PSLs off the exterior PPE surface or opening of the patient room door. Future work will further explore the potential for re-aerosolization of particles off of PPE during doffing. The present study provides the groundwork for a systematic method for evaluating the BCU and doffing procedures for their respective safety, and it also pilots a systematic method for evaluating potential pathogen exposure pathways for BCU healthcare workers.