Hospital Ventilation: A Hidden Risk for Virus Spread

Hospitals play a crucial role in treating infectious diseases, including viral illnesses like COVID-19 and influenza. Given the airborne nature of these infections, ventilation systems and air purification devices are widely used to control the spread of pathogens. However, a recent study conducted by researchers at University College London (UCL) and University College London Hospitals (UCLH) suggests that these very measures might have unintended consequences. The study, published in Aerosol Science & Technology, highlights how built-in mechanical ventilation and Portable Air Cleaners (PACs) may inadvertently contribute to virus spread instead of reducing it.

The Role of Ventilation in Hospitals

Ventilation in healthcare settings is designed to dilute airborne contaminants, improve indoor air quality, and prevent infection transmission. Mechanical ventilation systems use ducts and fans to circulate fresh air, while PACs help remove harmful particles. The assumption has been that increasing airflow reduces the concentration of viral particles, thereby lowering infection risks.

However, the study by UCL and UCLH challenges this assumption by showing that airflow devices can actually redistribute viral particles, potentially moving them into unexpected areas of hospitals. This discovery has significant implications for infection control policies and the design of hospital ventilation systems.

Study Methodology

To understand how airborne particles travel in a hospital setting, researchers conducted experiments in a hospital outpatient clinic at UCLH, central London. The clinic comprised:

• A large central waiting area (154 m³) divided into sections A and B
• Eight surrounding consulting rooms (each ~35 m³)
• A nurses’ station
• A permanently open passageway connecting to a corridor leading to the hospital

The experiments were conducted at night and on weekends to ensure no patients or staff were present, allowing researchers to track the movement of airborne particles in a controlled environment.

To simulate real-world conditions, the team used:

1. Aerosol generators (dispersing saline solution) to represent respiratory particles from an infected person
2. Particle counters to track how far and in what direction the aerosols traveled
3. Different airflow scenarios, including:
   • Doors open vs. closed
   • PACs switched on vs. off
   • Various placements of ventilation systems

The study revealed several counterintuitive findings regarding the movement of airborne viral particles.

1. Ventilation and PACs Can Spread Viral Particles Further
   • While PACs were expected to reduce airborne particle spread, in some cases, they increased it by up to 29% between neighboring rooms.
   • Built-in mechanical ventilation increased aerosol movement across the clinic by up to 5.5 times compared to no ventilation.
2. Closing Doors Significantly Reduces Particle Spread
   • When all doors were open, particles traveled freely to different rooms.
   • Closing the source room’s door reduced spread, and closing both the source and neighboring room doors cut transmission by 97%.
3. Larger PACs Can Introduce Unpredictable Air Currents
   • While PACs filter out viral particles, their exhaust vents generate new airflows.
   • In some cases, air currents redirected unfiltered particles, spreading them to unintended areas instead of capturing them.
4. Complex Airflow Patterns Create “Hotspots”
   • Particles sometimes accumulated in rooms far from the infection source.
   • One experiment showed 184% more particles in a distant room compared to the expected average, while the room directly opposite the infection source had 68% fewer particles.
   • The nurses’ station—where hospital staff frequently move—had the highest particle concentration, making it a high-risk area for infection.
5. PAC Placement Matters
   • Large PACs in the waiting room increased spread to adjacent rooms by 29%.
   • Small desktop PACs placed in multiple locations helped reduce spread more effectively.
   • Proper positioning of PACs and ventilation systems could be a simple solution to minimizing risks.

Implications for Hospital Infection Control

These findings have serious implications for hospitals and policymakers. Rather than simply increasing ventilation, hospitals must carefully assess airflow dynamics before deploying PACs or ventilation systems. Some key takeaways include:

1. Strategic PAC Placement is Critical
   • Hospitals should model airflow patterns before installing PACs.
   • Larger PACs should be placed where they won’t unintentionally spread particles.
   • Multiple small PACs may be more effective than a single large PAC.
2. Doors Play a Major Role in Containing Airborne Spread
   • Keeping doors closed where possible can drastically reduce virus transmission.
   • Hospital design should incorporate better door and ventilation coordination.
3. Understanding Local Airflow Can Improve Infection Control
   • Older hospitals with natural drafts will likely have more unpredictable airflow, requiring custom solutions.
   • Real-time airflow monitoring should be implemented in key areas such as waiting rooms and nurses’ stations.

Future Research and AI-Based Solutions

Given the complexity of airflow dynamics, researchers are now working on an AI-powered system to predict and measure particle movement. This machine learning model will analyze:

• Real-time airflow changes
• PAC placement effects
• Different hospital layouts

This AI system could eventually help governments and hospitals develop better NHS ventilation standards to minimize infection risks and prepare for future pandemics.

The study by UCL and UCLH has shed light on the unexpected ways ventilation and air cleaners influence virus spread in hospitals. While airflow devices are essential in controlling airborne infections, their misuse or improper placement can exacerbate the problem instead of solving it.

To ensure safer hospital environments, airflow patterns must be carefully studied, and strategic PAC placement must be prioritized. Additionally, closing doors and real-time airflow monitoring can play a major role in limiting infection transmission. With ongoing research and AI-powered predictive tools, hospitals can optimize their infection control strategies, ultimately making healthcare facilities safer for patients and staff alike.