Despite decades of advances in cleaning, sterilisation, and clinical protocols, healthcare-associated infections (HAIs) remain a persistent challenge. While significant progress has been made in controlling surface and instrument-related risks, increasing attention is now being given to the role of the built environment itself, where infrastructure systems such as water, air, and drainage operate continuously and may act as sources of microbial contamination. Here, Jørn Terkelsen, founder and CEO of Dolphin Care, looks at whether infection prevention strategies are addressing all relevant pathways of contamination within clinical environments.
In many healthcare settings, responsibility for infection prevention is divided between clinical teams and estates or facilities departments. While this reflects organisational structure, it may also create gaps in how environmental risks are addressed.
Clinical teams focus on patient-facing interventions such as cleaning, disinfection, and aseptic technique. Meanwhile, infrastructure systems, including ventilation, water systems, and drainage, are often managed with a focus on performance and compliance, rather than microbiological impact.
As a result, certain contamination pathways may be under-recognised. Even in well-managed environments, microbial reservoirs within infrastructure systems may persist and contribute to ongoing contamination.
Water systems and hidden reservoirs
Hospital water systems have received increasing attention in recent years, particularly in relation to biofilm formation within plumbing and drainage systems.
Biofilms provide a stable environment in which microorganisms can survive and proliferate, often protected from routine cleaning and disinfection practices. In clinical areas such as endoscope reprocessing rooms, sinks may therefore act as persistent environmental reservoirs.
While surface cleaning reduces contamination on visible surfaces, it does not address microbial load within underlying infrastructure. This creates the potential for repeated recontamination of the surrounding environment.
Recent work published in the Journal of Hospital Infection has further highlighted the role of sinks as potential sources of environmental contamination. Studies have demonstrated that microorganisms present within drainage systems can be dispersed into the surrounding environment through splash events, including Gram-negative organisms and, in some cases, strains associated with patient infections.
These findings reinforce the importance of considering not only visible surfaces but also underlying infrastructure when addressing persistent contamination.
Case study: identifying the source of contamination
A clinical investigation in a hospital setting highlighted the importance of looking beyond surfaces and equipment when addressing persistent contamination.
Despite thorough cleaning protocols, recurring microbiological findings prompted further investigation. Initial focus was placed on clinical equipment and procedures, but no clear source could be identified.
Attention then shifted towards the surrounding infrastructure, including the drainage system. Following installation of UV-C-based water trap technology targeting the drainage system, no further cases were detected over a period exceeding three years.
This shifted the focus from clinical processes to the surrounding infrastructure as the likely source of contamination, illustrating how hidden reservoirs may influence outcomes in ways that are not immediately visible.
Clinical environments: when infrastructure becomes part of infection prevention
One of the challenges in addressing environmental contamination is that infrastructure systems are often not considered part of routine infection prevention strategy. Water systems, drainage, and air handling are typically viewed as engineering functions rather than clinical risk factors.
However, growing attention is now being given to the role of hospital infrastructure in supporting infection prevention and antimicrobial resistance (AMR) strategies. Recent European discussions around AMR preparedness have highlighted the importance of integrating infection prevention expertise into hospital design, environmental management, and infrastructure planning.
In practice, this means recognising that contamination pathways may originate from the built environment itself.
In one clinical investigation involving an endoscope reprocessing environment, repeated microbiological findings persisted despite established cleaning protocols. Attention eventually shifted away from equipment and staff procedures towards the drainage infrastructure beneath the sink environment.
Following installation of targeted UV-C-based intervention within the drainage system, no further cases were detected during more than three years of follow-up.
Similar observations have been made in airborne contamination studies. In one highly controlled intensive care unit environment, continuous air treatment resulted in reductions in airborne microbial load of more than 80 per cent, despite already low baseline levels. In a separate NHS hospital evaluation, airborne contamination levels exceeding 1300 CFU/m³ were reduced dramatically within the first hour of operation.
Together, these examples illustrate how infrastructure-focused interventions may complement traditional infection prevention strategies by addressing continuous environmental contamination pathways that are otherwise difficult to control through episodic cleaning alone.
Airborne contamination in controlled environments
Airborne transmission is another pathway that has gained increasing attention, particularly in the context of respiratory infections. However, even outside of pandemic scenarios, airborne microbial load may play a role in environmental contamination.
A key assumption in many healthcare environments is that modern ventilation systems provide sufficient control of airborne contamination. While ventilation is critical, it may not fully eliminate localised microbial load within occupied spaces.
Testing conducted in a highly controlled intensive care unit environment demonstrated that even where baseline contamination levels were relatively low, continuous air treatment could achieve significant further reductions. Within the first two weeks, reductions in airborne microbial load of more than 80 per cent were observed.
This finding suggests that even ‘clean’ environments may still contain a measurable and reducible microbial burden.
Rapid reduction in high-load environments
The impact of continuous air treatment is not limited to low baseline environments.
In an independent evaluation conducted within an NHS hospital setting, baseline airborne microbial levels exceeded the upper detection limits of the sampling method (>1300 CFU/m³).
Following activation of the system, a rapid reduction was observed. Within approximately 30—50 minutes, levels fell to around 200—400 CFU/m³.
The speed and magnitude of this reduction highlight the potential for continuous air treatment to stabilise environments that would otherwise be considered highly contaminated.
Together, these findings suggest that continuous air management may be relevant across a wide spectrum of clinical environments — from highly controlled intensive care units to more heavily burdened ward settings.
Rethinking air quality: beyond ventilation alone
These findings align with a broader shift in thinking around indoor air quality. Research from the Harvard T.H. Chan School of Public Health ‘Healthy Buildings’ programme has highlighted the importance of air changes per hour (ACH) in reducing airborne risk, suggesting that levels of 4—6 ACH represent good to ideal conditions in many healthcare environments.
However, achieving these levels consistently across all clinical spaces is not always feasible, particularly in older infrastructure or high-occupancy settings.
As a result, increasing attention is being given to the role of localised air treatment solutions as a complement to central ventilation systems. These approaches aim to reduce microbial load directly within the occupied zone, rather than relying solely on dilution through air exchange.
From episodic to continuous control
Traditional infection prevention strategies are largely episodic in nature. Cleaning, disinfection, and sterilisation are typically performed at defined intervals or following specific events. While these interventions are essential, they may not address continuous sources of contamination originating from environmental systems.
Persistent contamination may instead be driven by ongoing inputs from infrastructure systems, including air and water. In such cases, episodic interventions alone may not be sufficient to achieve sustained control.
This has led to increasing interest in approaches that provide continuous environmental management, complementing existing protocols rather than replacing them.
Implications for operating theatres
Operating theatres represent some of the most highly controlled environments within healthcare. Strict protocols, advanced ventilation systems, and controlled workflows are designed to minimise infection risk.
However, even in these environments, contamination pathways may still exist.
Airborne particles, staff movement, and interaction with equipment all contribute to the dynamic nature of the operating theatre environment. Even small fluctuations in airborne microbial load during procedures may have implications for surgical site infection risk, particularly in longer or more complex operations.
While ventilation systems provide essential background control, localised microbial load may still vary significantly within the occupied zone.
The ability to continuously reduce airborne microbial load, even in already controlled environments, may therefore represent an additional layer of protection.
This raises an important consideration: should infection prevention strategies in operating theatres evolve to include continuous environmental control alongside existing episodic interventions?
Conclusion
Infection prevention has achieved significant progress through improvements in clinical protocols, cleaning, and sterilisation.
However, growing evidence suggests that hidden environmental reservoirs within infrastructure systems may play a more important role than previously recognised.
Addressing these challenges does not require replacing existing practices, but expanding them. By integrating infrastructure-focused strategies alongside established protocols, healthcare systems may be better equipped to reduce persistent contamination and improve patient safety.
The question is no longer whether surfaces are clean — but whether the entire clinical environment is truly under control.
Jørn Terkelsen
Jørn Terkelsen is the founder and CEO of Dolphin Care. Over the past decade, he has worked in close collaboration with clinical microbiologists and infection prevention specialists at Copenhagen University Hospital (Rigshospitalet) and other healthcare institutions to develop UV-C-based technologies addressing hidden environmental reservoirs of contamination in clinical settings. His work focuses on translating clinical microbiology insights into practical engineering solutions for infection prevention and environmental control.