Environmental control as a means of preventing nosocomial infections in the intensive care unit – selected issues

INTRODUCTION

Nosocomial infections are infections that develop in connection with the provision of healthcare services in healthcare facilities (hospitals, healthcare centres) as well as in nursing homes and hospices. However, it is in hospitals that the highest proportion of infections is recorded, mainly in wards with increased patient care where many medical procedures are performed and where the patient’s condition is unstable and requires intensified treatment and care. Intensive care units are widely considered to be “epicentres of hospital-acquired infections”. The report of the National Antibiotic Stewardship Programme (Narodowy Program Ochrony Antybiotyków – NPOA) on active monitoring of infections in anaesthesiology and intensive care units conducted in Poland in 2018 indicates that nosocomial pneumonia (PN), bloodstream infections (BSI), including catheter-related infections, and urinary tract infections (UTI) are the most common hospital-acquired infections [1]. The report is based on the results obtained from intensive care units in 11 centres with an active infection monitoring programme following the ECDC – European Centre for Disease Prevention and Control protocol.

SYSTEMIC INFECTIONS IN THE INTENSIVE CARE UNIT – AETIOLOGICAL FACTORS

In 2008, the acronym ESKAPE was used to describe the 6 bacterial species most frequently causing serious hospital-acquired infections, i.e. Enterococcus faecium, Staphylococcus aureus, Klebsiella pneumoniae, Acinetobacter baumannii, Pseudomonas aeruginosa, and Enterobacter sp. [2]. Importantly, these pathogens are the cause of most infections in intensive care units, as confirmed by numerous studies both in Poland and internationally [3-8]. An important agent of pneumonia in patients in intensive care units is Pseudomonas aeruginosa, which unfortunately shows resistance to carbapenems in almost every fifth case [3]. Numerous cases of pneumonia are also caused by gram-negative, non-fermenting bacteria of the genus Acinetobacter baumannii, with as high as 61.8% resistance to carbapenems in bacteria belonging to the genus Acinetobacter (data from the NPOA 2018 report) [3]. In a single-centre study conducted in a hospital in southern Poland, up to 508 nosocomial infections were found in 1854 patients hospitalised in the intensive care unit between 2012 and 2021, and 106 (8.9%) of all hospitalised patients were diagnosed with pneumonia, where the predominant pathogen was Acinetobacter baumannii (28.4%) [9]. As proven by studies, the Acinetobacter baumannii species presents phenotypic multiresistance and both constitutes the microbiota of the intensive care unit environment and is a cause of high mortality in the course of infections caused by this species [10]. In addition, it is worth noting that patients who have achieved clinical improvement in the intensive care unit return to various hospital wards where further therapy is continued. Many of these patients are diagnosed with a nosocomial infection that developed in the intensive care unit [11]. There is a real risk that they may become a vector transmitting microorganisms, especially highly resistant Acinetobacter or Pseudomonas [12].
Bloodstream infections (BSI), including catheter-related infections, also represent a significant proportion of infections in intensive care units. In these infections, the predominant pathogens are gram-negative bacteria, often including Pseudomonas aeruginosa. In a report given by the NPOA in 2018, the incidence of BSI was as high as 10.4 per 100 hospitalisations. Due to the need for complex infusion therapy and the need to administer potent drugs, which tend to irritate the vascular endothelium, as well as the application of parenteral nutrition, it is essential for patients hospitalised in intensive care units to have central vascular accesses. As reported in several studies [13, 14], the use of central catheters is associated with a higher risk of bloodstream infection, compared to the use of peripheral catheters. Hence, central line-associated bloodstream infection (CLABSI) poses a major clinical problem. Clinical forms of CLABSI include asymptomatic catheter colonisation, catheter insertion site infection, and catheter-related sepsis. Gram-positive bacteria (mainly of the genus Staphylococcus) are far more frequently responsible for vascular catheter colonisation. Although coagulase-negative staphylococci are the most common cause of these bloodstream infections, their isolation from blood cultures most often indicates contamination of the sample. Epidemiological data suggest that between 13% and 33% of infections are caused by fermenting and non-fermenting gram-negative bacilli (Escherichia coli, Klebsiella sp., Pseudomonas aeruginosa). It is worth noting that fungi (primarily yeast-like fungi of the genus Candida) may be an important factor in vascular access infections, contributing to 3-8% of the total number of infections [15]. In recent years, an increase in nosocomial infections caused by fungi has been widely reported. From the data concerning specific groups of patients, e.g. those treated in burn units, it appears that such an increase concerns not only systemic infections, but also infections of vascular accesses. A single-centre study conducted at the Malopolska Burn and Plastic Centre (Małopolskie Centrum Oparzeniowo-Plastyczne) noted an increasing trend in the contribution of Candida albicans to the aetiology of nosocomial infections [16]. To establish the diagnosis of microbiologically confirmed peripheral catheter-associated infections, it is important to follow an algorithm that involves collecting blood for testing at least twice on the same day or on consecutive days from at least 2 independent sites (e.g. blood from a peripheral vessel + blood from the lumen of a vascular catheter, and if the vascular catheter is a multilumen one, the sample should be taken from the most frequently used catheter lumen or from more than one catheter lumen). Such a procedure allows the avoidance of overdiagnosis of infections with physiological microbiota, mainly present on the skin. The following are considered to be commensal microorganisms: Corynebacterium spp. (except C. diphtheria), Bacillus spp. (except B. anthracis), Propionibacterium spp., coagulase-negative staphylococci (including S. epidermidis), viridans group streptococci, Aerococcus spp., and Micrococcus spp. [17].
Urinary tract infections (UTIs) are the most common form of systemic nosocomial infections, accounting for about 40% of all infections recorded in hospitals; however, their incidence is lower in intensive care units, at 4-7.25/100 hospital admissions [1, 18]. The most common cause of urinary tract infections is gram-negative Enterobacteriaceae, of which Escherichia coli predominates, especially the uropathogenic strains (uropathogenic Escherichia coli – UPEC). In uncomplicated infections, E. coli is responsible for 75-95% of cases, whereas in complicated cases its proportion drops to 40-50% while the proportion of other gram-negative Enterobacteriaceae (Proteus spp., Klebsiella spp., Providencia spp., Enterobacter spp.) and non-fermenting Enterobacteriaceae (P. aeruginosa and Acinetobacter spp.) increases significantly. A single-centre study conducted for 3 years in an intensive care unit of the University Hospital in Wrocław showed that urinary tract infections were diagnosed in 7% of patients hospitalised in this unit. In this study, a urinary catheter was used in 92.21 ±4.51% of patients during 14,006 patient-days and 12,917 days of bladder catheterisation. The main CA-UTI pathogens included Enterococcus spp., Acinetobacter baumannii, Klebsiella pneumoniae, Pseudomonas aeruginosa, and Candida spp. [18]. Studies in other centres also point to the predominance of Enterobacteriaceae family pathogens as an aetiological agent of infections. It is noteworthy that almost all patients hospitalised there had urinary catheters and their health status could be described as severe [19-21].

ENVIRONMENTAL CONTROL AND THE INCIDENCE OF INFECTIONS

Infections belong to the most common adverse events that occur during the provision of healthcare services. Generally, it is not possible to eliminate infections during the treatment and care provided to patients in the intensive care unit, but it is possible and desirable to reduce their occurrence. These measures can be taken by eliminating risk factors, selecting the most appropriate methods of treatment and caring for the patient, and monitoring existing infections to prevent them from spreading within the ward, hospital, or outside the healthcare facility.
The control of the intensive care unit environment is a set of multiple systemic and individual actions aimed at reducing and eliminating risk factors for infections. These factors are numerous and include the following: ward design, patient distribution (including the possibility of using isolation due to transmission routes), ward equipment, hand hygiene in the sense of washing and disinfecting hands and using or not using protective gloves, decontamination of hand disinfection containers and water intakes, and the installation of sinks limiting microbial contamination. These measures also include the following: limiting the number of rooms where “clean” and “dirty” pathways cross, developing rules for cleaning rooms and training cleaning staff, minimising staff turnover within a ward, avoiding hiring people from other wards, assessing the cleanliness of hospital rooms (various methods in the absence of recommendations for routine control of environmental microbiological cleanliness), developing rules for decontamination of equipment and its storage, and conducting epidemiological investigations in cases of nosocomial infections and epidemic outbreaks. The importance all these elements can be seen from studies in which, for example, it was shown that placing a patient in a room where a patient had previously been hospitalised with a multi-resistant microorganism, e.g. methicillin-resistant Staphylococcus aureus (MRSA), vancomycin-resistant Enterococcus (VRE), P. aeruginosa and A. baumannii, significantly increases the risk of colonisation or infection caused by this microorganism [22].
To prevent nosocomial infections, all possible factors influencing their occurrence should be identified. Factors are divided into modifiable, partially modifiable, and those beyond control of both the patient and the healthcare personnel. Factors that are subject to complete modification include the hygiene of the hospital environment – cleaning the premises in accordance with the rules and by trained staff, staff hand hygiene (disinfection as the predominant procedure, including the technique used for implementing it and preparing hands for work, i.e. short and unlacquered fingernails, no jewellery according to the rule of nothing below the elbow), generally accepted and applied rules for wearing protective gloves, a clothing policy adopted and accepted by the staff, including a change of protective clothing per duty shift. Another important aspect is the application of procedures limiting the touching of the patient and the protection of clean places from contamination, also by visitors, with the aim of limiting/minimising visits, especially by those not instructed in how to behave around the patient. A very important aspect is the behaviour of the ward staff, especially the observance of medical procedures (e.g. wound care, ‘catheter care’, bladder catheter supervision, or management of mechanically ventilated patients). Each staff member is required to comply with the standards covering the operation of the hospital ward, particularly the adherence to clearly defined procedures adopted in the ward [23-26]. In a study conducted in one neonatal intensive care unit, it was found that the transfer of, for example, microbially contaminated (Bacillus spp.) patient order sheets from the patient station to the console worktops could be a vector for pathogen transmission [27]. An outbreak of Stenotrophomonas maltophilia in the intensive care unit of a hospital in northern Italy was described. S. maltophilia was found to be identical in 6 patients, and it was also isolated from ward equipment, so the transmission may have occurred via cross-transmission during patient care [28].
In intensive care units, it is difficult in many situations to isolate the patient due to the routes of transmission (contact, air-droplet, and air-dust), the organisation of the ward, and its location in the hospital building. The universal principles of isolation for all patients refer to the application of standard isolation to each patient. Isolation is particularly important to prevent the spread of drug-resistant microorganisms or those with high epidemic potential, including MRSA, VRE, Clostridioides difficile, Enterobacteriaceae-producing carbapenemases (Klebsiella pneumoniae carbapenemases – KPC), metallo-B-lactamases (MBL), and OXA-48. Implementation of isolation is also important in the context of other pathogens: e.g. viruses such as influenza, RSV, rotavirus, norovirus, HBV, HCV, and HIV, or bacteria: tuberculosis, Neisseria meningitidis, and Streptococcus pyogenes. Isolation dependent on transmission routes and the associated intensification of activities in the intensive care unit results from an analysis of the epidemiological situation in the unit and is aimed at solving a problem that has arisen, such as the occurrence of an epidemic outbreak or the continuous importation of patients with a drug-resistant microorganism from another unit [29, 30]. A study conducted by researchers from Spain described a case of a patient with generalised skin lesions infected with Streptococcus pyogenes staying in a paediatric intensive care unit for 15 hours, which led to 4 streptococcal infections in healthcare workers. Phenotypic and molecular analyses of the strains showed that the 4 isolates, characterised as emm87/ST62/T28, were identical to the one obtained from the index case. The incidence of this outbreak, despite the patient’s short stay in the hospital and adequate treatment, highlights the high transmission capacity of the pathogen and, indirectly, the risk of underestimating the rules of patient isolation due to transmission routes [31].

PREVENTION OF THE MOST COMMON NOSOCOMIAL INFECTIONS IN THE INTENSIVE CARE UNIT AND MEDICAL PROCEDURES

Prevention of central vascular catheter (CVC)-associated infections involves educating medical staff to reduce the possibility of complications. Regular staff training plays a significant role in reducing the risk of vascular catheter-associated infections. This training should cover both the acquisition of vascular accesses and their maintenance, as well as using available equipment, with particular attention to the need for correct vascular line construction. It is important that training is carried out not only in simulated settings, but also in real clinical situations [32]. An important task, particularly on the part of the nursing staff, is to educate the patient and their carers about vascular access care, especially if the patient will end their hospitalisation with a vascular access such as an HD central catheter or vascular port. The risk of central line infections is determined by the following: the number of CVC channels, the type of catheter used for vascular access, the site of insertion, the use or not of a maximum protective barrier, active disinfection by wiping with a swab for approximately 15-30 seconds with the application of 0.2% chlorhexidine/isopropyl alcohol solution, or passive disinfection, i.e. using plugs soaked in a disinfectant, using dressings to tightly protect the vascular access, and washing the intensive care patient with antibacterial solutions. An important element in taking care of the vascular catheter is the correct construction of the vascular line with the application of extension drains to move the insertion site away from the injection port, the use of needleless connectors, and the flushing of the vascular access with 0.9% NaCl in a volume 2-3 times the dead space of the cannula and the vascular line elements using the bolus method. If parenteral nutrition is administered, one of the channels should be used for parenteral nutrition administration to reduce the risk of CVC colonisation. It is worth noting that when parenteral nutrition is administered via channels through which drugs and fluids are delivered, the risk of thrombosis and infection itself may increase [33, 34]. One study (meta-analysis) compared available dressings and fixation devices for CVC in terms of catheter-related bloodstream infection (BSI), catheter colonisation, entry and exit site infection, skin colonisation, skin irritation, failed catheter fixation, dressing status, and mortality. A total of 22 studies involving 7436 participants were included in the analysis, comparing 9 different types of fixing devices or dressings. All these studies were unclear or had a high risk of performance bias due to different designs of dressings and fixation devices. A multiple treatment meta-analysis showed that seamless fixation devices were probably the most effective in reducing the incidence of catheter-related BSI (low quality of evidence), with CGI dressings coming second (low quality of evidence). Medication-soaked dressings were found to reduce the incidence of catheter-related BSI more efficiently compared with all other dressing types. There is some evidence that CGI (chlorhexidine gluconate-impregnated) dressings are more efficient than SPU (standard polyurethane) dressings at reducing catheter-related BSI [35]. Another study evaluating catheter-associated bloodstream infections (CABSI) conducted in a 2100-bed hospital network in Switzerland between 2016 and 2022 reported 416 episodes of CABSI, including 60 episodes related to S. aureus infection and 92 episodes of CABSI where the infection involved gram-negative bacteria. The likelihood of gram-negative bacteria being the cause of CABSI was higher for long-term catheters compared with short-term CVCs without tunnelisation. Based on the study, it was concluded that the type of vascular catheter should be taken into account when choosing empirical antimicrobial therapies [36].
Prevention of respiratory infections, mainly ventilator-associated pneumonia (VAP), requires a comprehensive approach. As regards the care of the ventilator-assisted patient, intervention bundles, the so-called Bundle of Care – VAP, have been defined as a kind of guideline for clinical practice [37]. The package includes the following: positioning the patient in a head-up position (30-45°), providing a comprehensive oral hygiene service at least twice a day, and rinsing the patient’s mouth with chlorhexidine every 6-8 hours, as well as moistening the mucous membranes in the mouth, suctioning subglottic secretions, monitoring the depth of sedation, monitoring endotracheal tube cuff pressure, staff hand hygiene, periodic replacement of components of the breathing circuit such as the tube or filter, using closed suction systems, and using heat exchangers and heated humidifiers. It is also important to use appropriate filters in the ventilator system. In addition, the researchers emphasise the importance of pharmacological VAP prophylaxis, which is selective digestive decontamination (SDD), SDD with intravenous prophylaxis, and selective oral decontamination (SOD). The use of probiotics and drugs that affect the pH of gastric juice are also important in infection prevention. Based on these indications, there are numerous studies whose researchers have evaluated, for example, whether endotracheal tubes with subglottic secretion drainage (SSD) reduce the incidence of VAP among patients undergoing mechanical ventilation. A single-centre study in Poland showed that the use of endotracheal tubes with subglottic secretion drainage in ICU patients on mechanical ventilation significantly reduced the incidence of VAP [38]. The risk of VAP in patients in the intensive care unit was assessed based on a retrospective documentation analysis. A retrospective analysis of the records was performed and showed that the incidence of VAP was 4.7% and that the incidence rate per 1000 person-days of mechanical ventilation administered to these patients was 10.5. The most common aetiological agents of VAP were the bacteria Acinetobacter baumannii (36.4%), Pseudomonas aeruginosa (13.8%), and Escherichia coli (12%) [39]. This study also included a retrospective analysis of the medical records of patients after multi-organ trauma treated in the intensive care unit of the University Hospital in Krakow, who were diagnosed with pneumonia associated with mechanical ventilation. It was shown that patients infected with Staphylococcus aureus had a 4% chance of developing late VAP compared with Acinetobacter baumannii (p < 0.001), whereas patients infected with any other bacteria or yeast-like fungi were approximately 4 times less likely to develop late VAP compared with Acinetobacter baumannii (p = 0.02) [40]. Another study showed that the risk of VAP in ICU patients mechanically ventilated for at least 48 hours was increased by comorbidities such as chronic obstructive pulmonary disease, obesity, diabetes mellitus, and alcoholism, and these patients constituted a high-risk group for VAP [41].
Prevention of urinary tract infections associated with the use of a bladder catheter includes a series of actions, but this procedure should be chosen only as a last resort. In the intensive care unit, indications for urinary catheter insertion should be identified and monitoring of compliance with catheter care rules should be implemented. Insertion of the urinary catheter should follow the principles of asepticity including hand disinfection, wearing sterile gloves, and use of a sterile drape and sterile lubricant. The choice of catheter is not insignificant and, importantly, the routine use of catheters coated with antibacterial agents is not recommended. The most important aspects in catheter maintenance are to keep the system closed while it is being used, perform systematic perineal hygiene, empty the urine bag or change the bags, and to replace the catheter regularly. Furthermore, it is important to remove the catheter immediately when it is not needed. The use of antibiotics as prophylaxis for catheter-related urinary tract infection is not recommended [42-44].
In one US study, cycles of urinary tract infection prevention activities involving planning-activity-testing-activity and their impact on CAUTI rates were implemented sequentially in intensive care units. These activities included processes for inserting and maintaining Foley catheters, indications for permanent Foley catheters, appropriate testing for CAUTIs, alternatives to permanent devices, and sterilisation techniques. The studies have shown that such management is reasonable and has an impact on reducing the number of infections. Moreover, targeted educational activities and standardised checklists as well as sequentially adapted protocols are also low-cost and high-impact activities that can reduce CAUTIs in the intensive care setting [45].

SUMMARY

The intensive care unit is a place where the control and surveillance of nosocomial infections must follow strict rules aimed at protecting against adverse events such as these very infections.
Awareness of infection risk factors, their potential pathogenicity, and the fact that, in addition to known and reasonably well-controlled resident microorganisms, there are new and increasingly drug-resistant emerging pathogens, provides an opportunity for protection against them. Patient care in the intensive care unit requires interdisciplinary and interprofessional collaboration, where physicians together with nurses, physiotherapists, medical caregivers, laboratory diagnosticians, and other hospital staff perform a range of procedures that involve a risk of infection, but being aware of the risk of complications, they know how to take timely action to reduce their occurrence. Nevertheless, continuous updating of knowledge, improvement of existing skills, and self-monitoring at every level of treatment and patient care in terms of minimising environmental factors is the basis for the performance of every staff member working in the intensive care unit.

Disclosures

This research received no external funding.
Institutional review board statement: Not applicable.
The authors declare no conflict of interest.

References