Overcrowding in Emergency Departments (EDs) is a phenomenon that is now widespread globally and causes a significant negative impact that goes on to affect the entire hospital. This contributes to a number of consequences that can affect both the number of resources available and the quality of care. Overcrowding is due to a number of factors that in most cases lead to an increase in the number of people within the ED, an increase in mortality and morbidity, and a decrease in the ability to provide critical services in a timely manner to patients suffering from medical emergencies. This phenomenon results in the Emergency Department reaching, and in some cases exceeding, its optimal capacity. In this review, the main causes and consequences involving this phenomenon were collected, including the effect caused by the SARS-CoV-2 virus in recent years. Finally, special attention was paid to the main operational strategies that have been developed over the years, strategies that can be applied both at the ED level (microlevel strategies) and at the hospital level (macrolevel strategies).

Serratia marcescens belongs to the family Enterobacteriaceae, which is commonly found in water, soil, animals, insects, plants. Although S. marcescens displays relatively low virulence, it causes nosocomial infections and outbreaks in severely immunocompromised or critically ill patients, particularly in settings such as intensive care units (ICUs), especially neonatal units (NICUs). This microorganism gives rise to a wide range of clinical manifestations in newborns: from asymptomatic colonization to keratitis, conjunctivitis, urinary tract infections, pneumonia, surgical wound infections, sepsis, bloodstream infection and meningitis. The most frequent site of infection is the bloodstream, followed by the respiratory apparatus and the gastrointestinal tract. Strains of S. marcescens involved in epidemic events have frequently proved to be multi-resistant. Indeed, this species displays intrinsic resistance to several classes of antibiotics. Often, the specific source of the infection cannot be identified. However, the contaminated hands of healthcare workers are believed to be a major vehicle of its transmission. In neonatal intensive care units, colonized or infected newborns are the main potential source of S. marcescens, particularly in the respiratory apparatus, but also in the gastrointestinal tract. The early identification of colonized or infected patients and the prompt implementation of infection control measures, particularly rigorous hand hygiene and contact precautions, are essential in order to curb the spread of infection.

Pseudomonas aeruginosa is a Gram-negative pathogen that has become an important cause of infection in humans and can be associated with significant morbidity and mortality. Severe infections usually affect immunocompromised patients or those with chronic debilitating diseases. Its significance as a pathogen is exacerbated by its resistance to antibiotics, virulence factors and its ability to adapt to a wide range of environments. P. aeruginosa can have multiple intrinsic or acquired mechanisms of resistance, frequently with high resistance rates to various antimicrobial classes. In recent years, the worldwide spread of the so-called ‘high-risk clones’ of multidrug-resistant or extensively drug-resistant P. aeruginosa has become a public health threat that needs to be studied and managed with urgency and determination. Among Gram-negative infections, P. aeruginosa is one of the most common Gram-negative bacteria causing nosocomial and healthcare-associated infections in hospitalised patients. According to WHO guidelines, measures to prevent the transmission of multiresistant P. aeruginosa in healthcare facilities should include at least hand hygiene (with the appropriate use of alcohol-based solutions), contact precautions, patient isolation (single room or cohort), environmental cleanliness and surveillance.

Demographic studies show that life expectancy is increasing in developed countries; increased longevity has also increased the share of the older population with often concomitant chronic conditions. An ageing population and increased comorbidities lead to more complex pharmacological therapies (polypharmacy). The particular picture provided by chronic conditions and polypharmacy can lead to longer hospital stays and a greater need for healthcare. Elderly patients are identified as being in the high-risk group for the development of healthcare-associated infections (HAIs) due to the age-related decline of the immune system, known as immunosenescence. Comorbid conditions can often complicate infections, diminishing our ability to treat them effectively. Respiratory tract infections are the most common healthcare-associated infections, followed by urinary tract infections. HAIs in geriatric patients are responsible for longer hospital stays, extended antibiotic therapy, significant mortality, and higher healthcare costs. This is because the microorganisms involved are multidrug-resistant and, therefore, more difficult to eliminate. Moreover, geriatric patients are frequently transferred from one facility (nursing homes, skilled nursing facilities, home care, and other specialty clinics) to another or from one hospital ward to another; these transitions cause care fragmentation, which can undermine the effectiveness of treatment and allow pathogens to be transferred from one setting to another and from one person to another. Multifactorial efforts such as early recognition of infections, restricted use of invasive devices, and effective infection control measures (surveillance, isolation practices, hand hygiene, etc.) can contribute to significant reduction of HAIs in geriatric patients.

Candida auris has become a major concern in critical care medicine due to the increasing number of immunocompromised patients and candidiasis is the most frequent cause of fungal infections. C. auris and other fungal pathogens are responsible for at least 13 million infections and 1.5 million deaths globally per year. In immunocompromised patients, infections can quickly become severe, causing wound infections, otitis and candidemia, resulting in high morbidity and mortality. The clinical presentation of C. auris is often non-specific and similar to other types of systemic infections; in addition, it is harder to identify from cultures than other, more common types of Candida spp. Some infections are particularly difficult to treat due to multi-resistance to several antifungal agents, including fluconazole (and other azoles), amphotericin B and echinocandins. This entails treatment with more drugs and at higher doses. Even after treatment for invasive infections, patients generally remain colonized for long periods, so all infection control measures must be followed during and after treatment of the C. auris infection. Screening patients for C. auris colonization enables facilities to identify individuals with C. auris colonization and to implement infection prevention and control measures. This pathogenic fungus shows an innate resilience, enabling survival and persistence in healthcare environment and the ability to rapidly colonize the patient’s skin and be easily transmitted within the healthcare setting, thus leading to a serious and prolonged outbreak.

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