1 Introduction

In this narrative review we discuss concepts of hospital building based on a selective literature overview and expert opinions from different fields including technical support, hospital planning and architecture as well as infection prevention and control. Global health promotion paves the way for the “Healthy Hospital” concept [1], which aims to provide effective medical care in best spatial conditions, minimizing the risk of cross-transmission of pathogens. The coronavirus infectious disease-19 (COVID-19) pandemic exposed many limitations in the preparedness, processes, logistics and infrastructure of most healthcare systems. Few hospitals were ready to handle the local challenges coming along with a global crisis.

Hospitals are work places, hosting employees and patients, and as such, they must protect both staff and patients. Particularly, the design of the built environment has a pivotal role in the prevention of cross-transmission of some pathogens and minimizing healthcare-associated infections (HAI) in hospitals.

2 Principles and concepts

2.1 Preventing cross-transmission

Pathogens such as bacteria, viruses, and fungi spread either directly from person to person, or indirectly by air or fomites. Direct transmission can occur between health workers and patients, but also across patients and health workers, and between visitors and patients. The two most common transmission pathways are direct body contact (hands) or inhalation of aerosols.

Spatial separation, distancing and disinfection of the patient environment and fomites are common prevention measures for cross-transmission by both contact and air. Spatial separation is very effective to prevent contact transmission of pathogens such as Clostridioides difficile, methicillin-resistant Staphylococcus aureus, Enterobacterales, non-fermentative bacilli, and viruses such as noroviruses, rotaviruses, or adenoviruses [2].

Airborne transmission occurs by droplets of various sizes (including aerosols). Most recently, the severe acute respiratory symptom coronavirus 2 (SARS-CoV-2), challenged the classical concept of droplet and aerosol prevention measures [3]. Proper hospital ventilation became more important for respiratory pathogens other than tuberculous mycobacteria. Speaking, coughing and sneezing produces a wide range of droplet sizes, aerosols and droplet nuclei [4]. Aerosols and droplet nuclei float in the air for a prolonged period of time but are very sensitive to air flow. In addition to face masks and the spatial separation in single rooms or by cohorting, adequate ventilation is perceived an effective prevention measure of transmission [5].

2.2 Hygiene

Good standards of hygiene help allow people to live and work in confined space [6]. This is especially important in healthcare institutions. The history of modern health institutions begins with Florence Nightingale, who presumably was the first “health manager” in the medical field. She proposed patient care in large, bright rooms with windows for ventilation and with sufficient distance between patient beds [7]. In addition, rooms needed to be functional, easy to clean, and to offer a good working environment for nursing staff.

Ignaz Semmelweis showed that cleaning hands with chlorinated lime significantly reduced the incidence of puerperal fever [8]; and although classical microbiology was still in its early days, his work suggested that infection was the result of contact transmission of pathogens by hands. It took another 150 years before hand disinfection was accepted as the most important measure for preventing cross-transmission and HAI in the scientific community [9].

The separation of “clean” and “unclean” is the basic organizational principle in infection prevention and control (IPC) [2, 10]. Clean supplies and contaminated waste must be stored in separate areas. The flow from clean to contaminated activities and materials must be defined for all hospital areas, and mixing or combining these activities should be avoided. Spatial separation as a concept follows this principle; thus, isolation reduces the transmission of pathogens.

2.3 Healthy hospitals

Hospitals are organizations with a public mandate in a political and socio-economic context. Health policy objectives, financial capacity and the level of care form a balanced triangle, in which structure, performance and cost must be balanced and fixed during hospital planning (see Fig. 1). Structure (building) and infrastructure follow costs and the defined performance mandate. The hospital is often the strategic center of a larger medical network. Thus, demographics, the availability of qualified personnel, and the local level of primary care by family doctors, clinics, rehabilitation, and welfare institutions, are further determinants for hospital planning.

Fig. 1
figure 1

“Relationship triangle” of hospital planning (COPYRIGHT Lohfert & Praetorius A/S)

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The construction of a hospital is the result of a long and careful planning process by politicians, public health authorities, health care institutions, developers, construction companies and users, but also by primary care providers and social welfare (Fig. 2).

Fig. 2
figure 2

Hospital planning in the context of demographics, public health, financial capacity, mission, organizational units and patient needs (Van de Zwart 2014, modified)

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Hospital buildings, staff, patients and work processes are self-contained social systems like small cities and their “residents” [11]. Each system is unique in its complexity, context and balance. Thus, the planning of new hospitals must address many elements on various levels.

The structure and organization of a hospital can be roughly divided into surgery, medical diagnostics and intervention, inpatient care, outpatient care, and administration, all of which are linked by staff, supplementary, technical and electronic logistics [2, 11].

2.4 Mapping infection prevention and control to architectural design

The structural and technical properties of the hospital must support operational and hygienic concepts. Transport systems, transport corridors and storage rooms as well as parking spaces for equipment and vehicles must guarantee that material and equipment remain clean and waste can be disposed safely.

Sufficient space for work organization is important in all hospital areas. Space is often limited due to service needs and defined costs. However, surface reduction makes logistics more complex both within as well as between units. Working space for health workers must be adaptable to the number of staff working in a unit. Local administrative work needs office-like work places. Separate rooms must be available to talk to patients and families in private. There must be rooms for recreational activities and meetings. Operating theatres, intensive care and neonatal units with their technical equipment and complex, invasive procedures, must have sufficient space to allow safe work and prevent the risk of cross-contamination.

Single rooms with individual sanitary units are preferable, and facilitate the principles of spatial separation and the separation of clean and contaminated. A number of studies have reported that single rooms reduce the spread of pathogens [12, 13]. Rooms must be large enough to allow ergonomic working and meet with families [14, 15]. Single or twin rooms with individual sanitary facilities (toilet and shower) have become standard in regular wards of new hospital buildings [13].

Logistics of navigating staff, patients, visitors and material through the hospital are challenging, but need to be defined. Transportation routes must be as short as possible and space in the corridors must allow the free circulation of beds, stretchers and wheelchairs. Where at all possible, clean material supplies and waste removal must not cross each other or the pathways of patients and public areas. Vertically developed buildings must have enough elevators and other ascending aids to allow uninterrupted traffic. Routes of employees must be separated from public areas for direct access to their (secure) wardrobes and work areas.

3 Building equipment and systems

The technical infrastructure in a hospital includes water supply, ventilation systems (air supply, exhaust air, heating and cooling), heating systems, transport systems, sewage systems, supply and storage rooms, and areas for reprocessing medical devices and fomites, e.g. cleaning, sterilization and disinfection units. Specifications of the engineering depends on the mission of the medical sectors. Operating rooms need different technical configurations than patient rooms, offices or recreational rooms. For most sectors, there are international, national and/or local technical standards. WHO addresses the need of a clean and/or hygienic environment in healthcare-facilities in its development of the strategy of infection prevention and control 2022, based on the core components of infection prevention and control [16]. The infection prevention and control team should be involved from the outset in the design and delivery of new facilities so that key principles underpinning the prevention and control of HAI are flagged and delivered.

3.1 Air systems

The supply of clean fresh air is essential for the wellbeing of patients and employees in a hospital. The heating/cooling, ventilation and air conditioning (HCVAC) system must be designed according to the mission of the hospital and spectrum of care. Supply inlets must be designed in such a way that particles carrying bacteria, spores and viruses are eliminated. Two air systems can be distinguished: (1) ventilation where air is supplied and extracted from certain rooms; and (2) air conditioning where, in addition to circulation, air is cooled/heated and moistened. Both systems can be equipped with filter systems.

For the safety of patients and staff, two types of “infection isolation rooms” can be distinguished: (1) protective environment (PE) rooms with positive air pressure for patients with severe immunosuppression; and (2) airborne infection isolation rooms (AIIR) with negative air pressure for patients with airborne infectious diseases. High efficiency particulate air (HEPA) filters control inflow and in certain cases also exhaust. In both room types, air must be changed every 5 min (12 air changes per hour) to reliably remove particles and aerosols that contain pathogens [17]. In order to maintain the pressure conditions at all times, the rooms must be equipped with sluices; and floors, ceilings and walls must be thoroughly sealed. The sluices serve as entry and exit areas. They must be adequately dimensioned for donning and doffing personal protection attire. In the UK, an alternative of a neutral pressure patient room accompanied by a positive pressure lobby and negative pressure ensuite facility ensures a safe environment patients with transmissible infections and those that are immunocompromised [18].

Natural room ventilation by window opening requires large windows to allow sufficient air exchange. This is only feasible in buildings with no windowless central zones and high ceilings and fly screens must be installed. However, dust as well as fungal and bacterial spores may enter through open windows, putting severely ill and immunocompromised patients at risk.

3.2 Water systems

The water system provides drinking water, clean water for personal hygiene and patient care, and the sewage system, but also medical steam or deionized water for drug preparation, diagnostics, washing machines etc.. Drinking water is not sterile. It contains non-pathogenic microorganisms in smallest quantities including Legionella species. But, pathogenic bacteria may multiply and form biofilms in stagnant and hand-warm water.

The best prevention of biofilm production is permanent water flow in tubes and pipes. Cold water pipes must not be located directly next to the hot water pipes. Otherwise, sufficient insulation must keep the fresh water cool and the hot water hot. As turbulent flow also favors biofilm formation, water pipes must be straight-lined with a minimum of turns, twists and connection points. Regular checks of physical parameters in accordance with national and international standards are pivotal.

Water-operated cooling towers are a particular area of using water in the hospital. As they may be contaminated with Legionella species, they must be located on the rooftop or somewhere remote, and be maintained continuously [19].

4 Waste management

Most waste in a hospital can be disposed as normal waste. Medical waste, e.g. organs, liquid blood and other infectious material defined by lists of infectious agents with potential transmission, is disposed only after appropriate disinfection or as biohazard material according to defined process. If stored for later incineration either on-site or out of the hospital, infectious waste must be kept at temperatures ≤ 15 °C. However, sustainability and addressing the challenges of reducing  the hospital carbon footprint are of increasing importance.

4.1 Electrical and information technology systems

Electricity and IT wiring must be planned anticipatorily, allowing modification and expansion as medicine relies on advances in electronic equipment and IT. Big data and data exchange will be pivotal in the future. IT networks will grow within and between hospitals. Artificial Intelligence, machine learning will be used increasingly in hospital epidemiology and infection control [20]. Additionally, “robots” will work not only in surgery but also in the maintenance and facility management [21]. The hospital environment of the future will be full of sensors for optimal medical care and HAI reduction.

4.2 Surfaces and materials

Hospital surfaces and furniture in rooms with patient contact must be functional and easy to clean and disinfect. Therefore, the surface material must be chemically resistant to UVC and common disinfectants such as 70% ethanol, aldehydes, and oxygen releasers.

5 Key clinical areas

5.1 Intensive care units

Intensive care units consist of patient rooms or bays, monitoring areas, recreational rooms, toilets for staff and visitors, storage rooms, sluices, and cleaning rooms. The spatial arrangement of the rooms must allow short distances for efficient work organization [22].

To minimize the risk of cross-transmission by multidrug-resistant organisms single rooms are preferred, particularly in burn units [12, 23, 24]. Patient rooms or bays must be sufficiently large to host an entire resuscitation team in addition to monitors, machines and medical equipment, and to allow access to the patient from all directions [25]. Ideally, the space should be sufficient to allow emergency surgical interventions by a surgical team, when and if required.

Electronic installations, tubing for medical gases and pressured air, and the HCVAC system must comply with the relevant industrial standards. A sufficient number of isolation rooms, ideally with the option to switch between positive or negative pressure must be available.

Instruments for point-of-care diagnostics do not necessarily need separate rooms but given the handling of biological fluids, should be placed in areas (unclean working rooms) where waste can be discarded easily.

5.2 Bone marrow transplant units

Patients with hematological diseases in bone marrow transplant units are severely immunocompromised and at a high risk for infection. These units need single positive pressure rooms with individual entry rooms, and individual toilet and shower. Supply air must be HEPA-filtered and changed every 5 min (12 air changes per hour) or more. The unit must have sufficient space for storing personal protective equipment, and for visitors to change clothes before entering patient rooms. Water and water systems have to be carefully planned and maintained to avoid the emergence of severe infection due to Pseudomonas aeruginosa and other other waterborne pathogens [26].

5.3 Security level 4 isolation units

Safety level 4 isolation units are needed for the care of patients with dangerous infections by highly contagious pathogens without treatment options such as Ebola hemorrhagic fever. In Europe, these specialist units are confined to just a few sites in every country, e.g. there is just one in Switzerland. International cooperation is pivotal [27]. These areas are like an independent building within a building with a separate air exhaust system and waste management. The entire unit is under negative pressure with the lowest pressure and adequate air exchange in the patient room. From a constructional point of view this needs sealed floors, ceilings, walls and windows. Exhaust air needs to be HEPA-filtered before being disposed directly outside the hospital. The patient room has no sewage unless waste water can be collected separately for inactivation. Liquid waste, including biological fluids, are removed in sealed containers after adding absorbent or solidifying material according to distinct regulations on disposal of biohazard material. The unit includes space for staff, laboratory, storage and waste. Storage areas must be extra-large, particularly for contaminated material in sealed safety containers before evacuation [28].

5.4 Infectious diseases units

Each hospital should have a specifically designed ward for patients with highly contagious infectious diseases, particularly airborne pathogens such as multidrug-resistant tuberculosis (28). Such units are separated from other care areas and have a sufficient number of negative-pressure rooms, each equipped with entry rooms and individual toilet and shower. The unit must have sufficient space for storing personal protective equipment.

5.5 Operating theaters (rooms)

Planning surgery units is complex, especially as now interventions that mirror surgery are undertaken by physicians and radiologists, e.g. interventional cardiologists and radiologists. Operational concepts, the separation of clean and contaminated, logistics, and technical aspects all need to be taken into account for efficient patient movements as well as supply storage and waste disposal. Standards for design and operation are available with regard to the room size and arrangement, the ventilation system and the side rooms. Although the role that air contributes to the development of surgical site infections is often not obvious, operating rooms may need air systems with HEPA filters and as an option controlled airflow (laminar airflow), such as for prosthetic joint surgery. These requirements are not applicable to all types of interventions. However, the types of surgery to be delivered must be addressed early in hospital planning to decide on room classes and the appropriate ventilation system. Room pressure is highest in the operating rooms, the instrument preparation rooms and the sterile goods area. Sufficient space must be planned for moving and preparing patients, storing clean and contaminated material, changing clothes, doing office work, and resting.

5.6 Outpatient areas

The COVID-19 pandemic made clear that waiting areas for patients must be larger. Space must allow sufficient distance for preventing transmission of airborne viruses. Ideally, waiting areas of infectious and non-infectious patients are separate. During epidemics or a pandemic these areas—of large enough and appropriately designed—may serve as triage areas. However, outside a pandemic where symptomatic patients are likely sharing the same pathogen, cohorting patients based on clinical signs may be considered sub optimal practice.

6 Health care workers and other professions

Besides health care workers, the hospital is the work place for a large range of professions such as technicians, pharmacists, laboratory staff, administrators, IT-specialists, service personnel, facility managers, cleaners, conveyors, cooks, preprocessors, craftsmen, teachers, and clergymen. The professional output of the hospital depends on the different professions working together. The organizational culture not only is the collective mindset of collaborators but also the level of service provision. In this way, intelligent logistics and infrastructure help staff performing at the highest achievable level and avoiding errors. The built facility must ease rather than complicate proper functioning of the hospital. Restricting or reducing space is one of the major flaws in planning because it complicates work to a level where errors occur due to adapting to space rather than space adapting to work organization.

7 Conclusion

Hospital planning must address a very high number of needs in a complex organization that offers a wide range of services. From an IPC perspective, contamination, cross-transmission and infection by microorganisms are the main principles to take into account. However, safety also depends on an environment that facilitates rather than complicates the work on patients because transmission of pathogens and healthcare-associated infections are mostly the result of the neglected complexity in work organization and stress. Infection prevention and control specialists should be involved early and consulted throughout the entire process of conceptualization, planning and executing a new hospital.