HOSPITAL-ACQUIRED INFECTIONS: MICROBIOLOGICAL CAUSES, TRANSMISSION PATHWAYS, AND PREVENTION STRATEGIES

Hospital-acquired infections (HAIs), also known as nosocomial infections, represent a major challenge to modern healthcare systems worldwide due to their high morbidity, mortality, and economic burden. These infections develop during hospitalization or medical care and were neither present nor incubating at the time of patient admission. The growing prevalence of HAIs is closely linked to invasive medical procedures, prolonged hospital stays, immunocompromised patient populations, and inadequate infection control practices. Understanding the microbiological causes of these infections is essential for effective prevention, diagnosis, and treatment strategies. Microbiologically, hospital-acquired infections are caused by a wide range of pathogenic microorganisms, including bacteria, viruses, fungi, and, less commonly, parasites. Among these, bacteria are the most frequent etiological agents, particularly multidrug-resistant organisms such as Staphylococcus aureus (including MRSA), Escherichia coli, Klebsiella pneumoniae, Pseudomonas aeruginosa, and Acinetobacter baumannii. These pathogens possess various virulence factors, including biofilm formation, toxin production, and antibiotic resistance mechanisms, which enable their persistence in hospital environments and resistance to standard therapies. Viral agents such as influenza viruses, respiratory syncytial virus, and norovirus also contribute significantly to HAIs, especially in intensive care units and pediatric wards. Fungal infections, mainly caused by Candida and Aspergillus species, are increasingly observed among patients with weakened immune systems. The hospital environment itself serves as a reservoir for pathogenic microorganisms, with contaminated medical equipment, healthcare workers’ hands, air, water systems, and hospital surfaces playing critical roles in transmission. This article aims to comprehensively analyze hospital-acquired infections with a particular focus on their microbiological causes. By reviewing current scientific literature and microbiological evidence, the study highlights the importance of strict infection control measures, continuous microbiological surveillance, and rational antimicrobial use in reducing the incidence of HAIs and improving patient safety.