Hospital ventilation could cause viruses to spread

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Equipment designed to mitigate the spread of viral infections in hospitals could cause viral particles to move around more, according to a new study from UCL and UCLH.

The clinic where the experiments took place consisted of a large central waiting room (154m3, split into A and B for the purpose of the study), eight surrounding consulting rooms and a nurses’ station (all approximately 35m3). The clinic was connected via a permanently open passageway to a corridor leading to the rest of the hospital. Experiments took place at night and weekends when no staff or patients were present
The clinic where the experiments took place consisted of a large central waiting room (154m3, split into A and B for the purpose of the study), eight surrounding consulting rooms and a nurses’ station (all approximately 35m3). The clinic was connected via a permanently open passageway to a corridor leading to the rest of the hospital. Experiments took place at night and weekends when no staff or patients were present - AdobeStock

In the study, researchers investigated the effect of using built-in mechanical ventilation and portable air cleaners (PACs) on the spread of airborne particles, which are similar to those breathed out by a person with a viral respiratory infection. Their work is detailed in Aerosol Science & Technology.

The team tracked the movement of airborne particles around a typical hospital outpatients’ clinic at UCLH in central London using an aerosol generator and particle counters. A variety of scenarios were simulated, including particle movement to a neighbouring room, throughout the whole clinic, and from one room to another room at the far side of the clinic.

They also tested whether factors such as closing doors, or the position of ventilation and PACs within a room, influenced the spread of particles.

The researchers found that while use of built-in ventilation and PACs can reduce particle spread in some scenarios, in some experiments the use of PACs increased aerosol spread by up to 29 per cent between neighbouring rooms. Built-in ventilation potentially increased aerosol migration across the clinic by up to 5.5 times more than if no ventilation was used.

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In a statement, Professor Laurence Lovat, senior author of the study from UCL Surgery & Interventional Science and UCLH, said: “The COVID-19 pandemic really highlighted the risk of picking up airborne viral infections in hospitals, which naturally led to efforts to reduce this risk. In many hospitals, the use of ventilation systems and portable air cleaners has increased.

“While the urgency of the situation demanded a rapid response, since then we’ve been studying precisely how viral particles move around in real spaces and have been surprised by what we’ve found.

“Putting air cleaners in rooms led to unexpected increases in the circulation of aerosols in some cases, but it took months to understand what we were seeing. Each scenario produced different, unexpected results, depending on the spaces and airflow sources involved.

“Even at UCLH, a modern hospital built less than 20 years ago, airflow patterns were not predictable. In older hospitals, which often have natural draughts, the situation would likely be even more complex.”

The study concluded that using airflow devices in hospitals to try to limit the movement of airborne pathogens requires careful consideration of airflow dynamics and device placement to reduce the risk of exacerbating the problem.

Given the unpredictability of how aerosol particles move around spaces and the difficulty in measuring them, the team is building an AI system to help to do this and hope to start testing within the next 18 months.

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