Over 2016 and 2017, NHS hospitals in England faced an estimated 834,000 healthcare-acquired infections (HCAIs). These accounted for 28,500 patient deaths, 7.1 million occupied hospital bed days and 79,700 days of absenteeism among frontline healthcare professionals. They also cost the NHS £2.7bn.
Later, during the Covid-19 pandemic from June 2020 to March 2021, around 131,000 patients acquired Covid while in hospital, accounting for 1.5% of all admissions.
Hygiene is crucial in all healthcare settings, as ill patients are the most vulnerable to disease or infection. It is estimated that approximately 25% of HCAIs are the result of airborne respiratory diseases, so maintaining the correct ventilation rates is essential. This will ensure that the air is clean and healthy, and that the air occupants exhale – which could be a potential source of infection risk – is removed or inactivated quickly.
However, increasing air-change rates indoors can be costly and disruptive if upgrades to existing systems are needed. Around 50% of NHS facilities are non-compliant with the minimum ventilation standards. Traditional methods of improving ventilation also have an impact on the availability of clinical spaces during renovations, potentially increasing waiting times. Further, higher ventilation rates increases energy use contradicting the government’s decarbonisation agenda.
Alternatives exist, however, that align with net zero aspirations and comply with the various guidelines, standards and regulations relating to healthcare building ventilation and infection control and prevention.
During the pandemic, portable air cleaning devices were used for short-term and temporary situations, but the longer-term strategy for the NHS estate is to install hardwired, high-level ‘upper room’ germicidal ultraviolet (GUV) air cleaning that uses a certain wavelength of light to disinfect the air closest to the source of airborne contamination risk (above the human-exhaled air plume).
Similar GUV technology could be applied to improve overall building ventilation using chemical-free photo-disinfection in HVAC systems. This is achieved by placing an array of GUV lamps within system ductwork, decontaminating air at source.
The science behind germicidal ultraviolet
When pathogens are exposed to GUV light of the correct intensity and exposure time, their DNA/RNA is reconfigured and damaged, rendering it harmless. This leads to safer buildings for patients, staff and visitors. Potentially allowing safely decontaminated air to be recirculated in more areas of the NHS estate will help the service hit net zero targets, allow greater use of workspace, and, theoretically, reduce waiting times.
The inactivation solution depends on the medium (air, water, surface), environment, hazard source, presence of people or animals, temperature, humidity, bio-load, exposure time, and the target microbe(s) that one seeks to eradicate. GUV lamps operate between 200nm and 280nm wavelengths of the electromagnetic spectrum by passing an electrical discharge through a low-pressure gas (including mercury vapour) enclosed in a soft glass or quartz tube.
The optimum wavelength for lamps to operate at is 254nm, when they are germicidal and most efficient at destroying microbiological matter. GUV emitters of 222nm, known as FAR UV, are currently being assessed for future potential and are less harmful to human skin and eyes.
HEPA filters are another alternative. Originally designed to stop radioactive material escaping from labs, they are effective at stopping microbes. They are energy-intensive, however, because filter pores to push air through are so small, and the pressure drop reduces the airflow significantly.
In summary the main options are:
Portable air cleaning units
Portable UVC or HEPA devices should only be considered as a temporary solution. When used, they must be positioned to avoid interference. They operate as recirculating air systems that pass air from the room through a decontamination chamber, which has a GUV light or a HEPA filter, and then discharges cleaned air back into the room. To be effective, they need clear space in front of their intake and their discharge grilles. Most portable units exceed NHS standards on noise.
GUV upper-room devices
GUV upper-room devices have been used for several decades to combat respiratory diseases. They were deployed successfully during the 2003 and recent Covid pandemics in Hong Kong hospitals. These devices were positioned between patient beds, and 2.7 metres off the floor, to intercept and disinfect exhaled air from the patients below.
Upper-room devices are a low-cost, intervention for areas with poor ventilation. They provide an equivalent decontamination rate and make up for shortfalls in conventional ventilation requirements, often exceeding 10 air changes per hour.
GUV in primary ventilation
Correctly engineered GUV lamps installed into HVAC ductwork, whether retrofitted into existing systems or incorporated into new hospitals, would enhance safety from respiratory-driven HCAIs. This intervention would make the NHS estate pandemic-resilient and reduce the burden of respiratory illnesses on hospitals.
Adding GUV light to building ventilation systems is a long-term investment with minimal maintenance. Some products can be linked to the BMS to optimise energy and ventilation rates. GUV is now suggested as a technology suitable for use in recirculation systems in the England Building Regulations and should be retrofitted in the NHS estate to ensure compliance with healthier building standards.
Few studies have been conducted on the impact of GUV on internal air quality. The next step is to run large trials to confirm the benefits in terms of electrical cost savings, reduced staff sickness, and reduced nosocomial infections. According to one report, potential savings could amount to £23bn per year1.
About the author
Mike Ralph is principal engineer at NHS Scotland Assure and a committee member on the CIBSE Healthcare Special Interest Group bit.ly/CIBHealth
References:
- Infection Resilient Environments Social Cost Benefit Analysis RAE June 2022, bit.ly/3WPmZjX
