Description
Healthcare-associated infections or nosocomial (derived from Greek nósos, illness, and komein, care) infections are infections that only occur after the patient has been admitted to hospital. This means the patient is not infected at the time of admission to hospital, although they may be colonised with various microorganisms, which in itself is a natural condition. To differentiate between regular and nosocomial infections in everyday practice, a simplified definition is used: infections that manifest themselves after the third day of hospitalisation are very likely acquired there and are therefore considered nosocomial while infections that arise within the first three days are considered as not having been acquired in hospital, i.e. were either brought in or acquired on an outpatient basis. What, then, are the possible sources and transmission pathways of nosocomial infections and how can they be addressed through hygiene measures in hospitals?
Endogenous and exogenous infections
The human body is populated with an average bacteria mass of 200 g (approx. 3 × 1013 bacterial cells). As most bacteria are much smaller than human cells, that means that our body contains about the same number of microorganisms as human cells (Sender 2016). The totality of these microorganisms is called human microbiome. Most bacteria are found in the gastrointestinal tract and fulfil a central function in the digestion and production of important metabolic products. Many bacteria are also naturally found on the skin and mucous membrane of the body. The intact skin, and also the intact intestinal mucosa, protects our body against penetration by microorganisms. Invasive medical procedures pierce this natural barrier and thus open up a channel for pathogens to enter otherwise non-microbial areas of the body. If the number of pathogens that make it into the body exceeds a critical quantity, the body’s own defence mechanisms are unable to contain them, or at least can only partially do so, resulting in an infection. In addition, bacteria can settle very effectively, especially on plastic surfaces, and once settled produce a slimy substance (the so-called biofilm) that protects them and promotes their unhindered reproduction (Fig. 2).
Common medical procedures in hospitals where this route of infection applies are surgical procedures, urinary tract catheterisation, artificial respiration by tracheal intubation, intravenous access, and so on. Most hospital infections are therefore endogenous in nature. This means that the infectious pathogens mostly stem from the patient’s own flora. In industrial nations, an estimated 85 % of all infections are assumed to be endogenous. Consequently, invasive procedures must be used very sparingly in order to minimise the risk of infection.
Some hospital-acquired infections are caused by pathogens that enter the patient from outside, from the surrounding environment. This so-called exogenous acquisition of infection is suspected to account for about 15 % of hospital infections. Most of these pathogens are transmitted directly, for example from the hands of hospital staff, or indirectly, through medical devices (e.g. a stethoscope or endoscope). Droplet, airborne or hospital water-borne transmission usually plays a secondary role in the genesis of nosocomial infections.
Through appropriate built measures, it is largely possible to reduce the proportion of exogenous infections. By creating a built environment that facilitates uncomplicated workflows and by creating positive incentives (so-called “nudging”), such as encouraging hand disinfection, it is also possible to reduce the risk of endogenous infections. In addition, an environment in which the patient feels comfortable and less exposed to supplementary stress factors can have a protective effect.
To begin with, one can prevent the transmission of airborne infections using built means, for example single-bed rooms with and without an airlock. The assumption is that single-bed patient rooms reduce the possibility of contact transmission of infectious pathogens. A separate room may offer a further incentive to remind people to disinfect their hands regularly. Single rooms are also presumed to be advantageous in preventing infection transmission resulting from the shared use of sanitary facilities.
The risk of hospital-acquired infections correlates to hospital size (number of beds), i.e. the proportion of patients with hospital-acquired infections increases with hospital size. This can be explained by the fact that hospitals at the end of the treatment chain generally admit more patients with more serious underlying health conditions. These hospitals are usually maximum care facilities with a large number of beds and a wider range of highly specialised disciplines.
The risk of infection also varies within the hospital depending on the respective department and discipline (Fig. 3). They are most prevalent in departments that frequently require invasive procedures such as intensive care units or after major operations, e.g. abdominal surgery. Other high-risk areas are those with patients whose immune systems are particularly weakened, such as oncology wards or wards with transplant patients. For this reason, infection prevention in these areas is especially important.
Hospital-acquired infections occur relatively constantly throughout the year. Seasonal fluctuations only occur for individual types of infection and pathogens. For example, post-operative wound infections are more frequently observed in summer. Viral gastroenteritis such as norovirus infection occurs more frequently in winter.
Horizontal and vertical prevention measures
In hospitals, a distinction is made between horizontal and vertical prevention measures. Horizontal measures are implemented equally for all patients. The most important example is hand disinfection with alcohol-based handrub by all patients and by all hospital staff in patient care. According to the scheme established by the World Health Organization (WHO 2009), hand disinfection is carried out before touching a patient, before clean/aseptic procedures, after body fluid exposure risk, after touching a patient and after touching patient surroundings (Fig. 4). Cleaning and disinfection are also part of the horizontal measures, as is the focused and sparing use of antimicrobial drugs. The latter is also controlled at hospital level as part of a so-called antibiotic stewardship programme (Leitlinie “Strategien” 2019). Antibiotic stewardship programmes are hospital-wide projects that regulate the prescription practice of antibiotics. This is often implemented by in-house teams (e.g. infectiologists), who implement a sort of quality management system for the entire hospital.
Vertical prevention measures are those that are only carried out with certain patients to prevent a specific pathogen or infection. For example, typical vertical prevention measures include screening for multi-resistant bacteria such as MRSA (methicillin-resistant staphylococcus aureus) and placing patients with MRSA bacteremia in a single room.
In order to plan and implement the appropriate preventive measures individually for each hospital, hospitals employ medical and nursing hygiene specialists. Almost all hospitals employ nursing staff with appropriate specialist training (so-called hygiene specialists) and larger hospitals also employ medical staff trained as hospital hygienists.
The main requirements for infection prevention in Germany are specified in the Protection against Infection Act and the respective federal state’s hygiene regulations. The Commission for Hospital Hygiene and Infection Prevention (KRINKO) at the Robert Koch Institute (RKI) is an expert committee that develops and publishes national recommendations for the prevention of healthcare-associated infections based on current publications and expert knowledge.
Because certain vital medical products such as vascular catheters (Fig. 5), urinary tract catheters, intubation tubes represent such a major potential source of infection, most of the KRINKO recommendations deal with the infection-preventive handling of these aids. Other recommendations focus on measures to prevent the spread of certain pathogens. Due to the small number of systematic studies of the influence of hospital design and planning on hygiene, these feature only rarely in the KRINKO recommendations.
References
Ron Sender, Shai Fuchs and Ron Milo, “Revised Estimates for the Number of Human and Bacteria Cells in the Body“, in: PLoS Biology 14 (8), 2016
WHO, “My 5 Moments for Hand Hygiene“, WHO Guidelines on Hand Hygiene in Health Care, 2009, https://www.who.int/infection-prevention/campaigns/clean-hands/5moments/en. Last accessed 5 March 2020
Leitlinie “Strategien zur Sicherung rationaler Antibiotika-Anwendung im Krankenhaus“, 2019, https://www.awmf.org/leitlinien/detail/ll/092-001.html. Last accessed 5 March 2020
Originally published in: Wolfgang Sunder, Julia Moellmann, Oliver Zeise, Lukas Adrian Jurk, The Patient Room, Birkhäuser, 2020.