Pathogens and Morbidity Structure
The distribution of infections within inpatient facilities is uneven. Purulent-septic infections hold an absolute lead, to which surgical patients are particularly vulnerable. In second place are nosocomial enteric infections (specifically salmonellosis and shigellosis), followed by viral hepatitis (accounting for about 6–7%) and other conditions.
The bulk of problems (about 90%) are associated with opportunistic microorganisms. When host resistance drops, they cause severe systemic pathology:
- Sepsis and meningitis: staphylococci (Staphylococcus aureus), Pseudomonas aeruginosa, Klebsiella spp., Haemophilus influenzae, and Candida species.
- Respiratory tract and ENT infections: classic pathogens (Streptococcus pneumoniae) and typical hospital gram-negative flora (Proteus spp.).
- Urinary tract pathology: enterobacteria dominate (Escherichia coli, Citrobacter spp., Serratia spp.).
About 10% of nosocomial infections are caused by obligate pathogens (influenza virus, rotavirus, Bordetella pertussis, Corynebacterium diphtheriae).
How Hospital Strains Form
The hospital environment is extremely aggressive for microorganisms. Constant exposure to ultraviolet radiation, desiccation, strong disinfectants, and antibiotics kills off weaker flora while leaving the hardiest survivors. Through continuous selection and dominance, hospital strains emerge—microbial variants perfectly adapted to the conditions of a specific inpatient facility.
Their main distinguishing features:
- Increased virulence: a minimal number of bacteria is sufficient for infection (reduced infectious dose) and pathogenicity factors show high activity.
- Specific adaptation: they are resistant to the antibiotics and antiseptics used in the hospital.
- High survival capacity: the microbes are undemanding regarding growth conditions.
- Constant circulation: there is an uninterrupted exchange of bacteria between patients and staff.
Artificial Transmission Mechanism and Risk Factors
The rise in nosocomial infection rates is directly linked to medical advancements. This phenomenon is known as the "paradox of progress." Aggressive therapy (immunosuppressants, radiation therapy), massive antibiotic use, and complex surgeries lead to patient debility.
During invasive procedures, an artificial transmission mechanism operates—evolutionarily unexpected portals of entry are created. The pathogen enters tissues devoid of local defense mechanisms (the peritoneal cavity, joints, pleural space, bloodstream).
High-risk procedures include:
- Diagnostic: blood collection, venesection, endoscopy, punctures, manual examinations (risk is higher with ulcers and erosions).
- Therapeutic: catheterization, intubation, mechanical ventilation, transfusions, organ transplantation, hemodialysis.
Passive vectors include mechanical ventilators, drainage tubes, endoprostheses, linens, and staff hands, while moist environments (faucets, sinks, floor drains) and air conditioning systems serve as epidemiologically hazardous reservoirs for microbial proliferation.
Diagnostic and Preventive Features
When a nosocomial infection is suspected, the microbiology laboratory's key task is to isolate the specific hospital strain. This involves epidemiological marking (determining serovars, phagovars, and antibiotypes). If multiple patients simultaneously harbor identical strains, it is a sign of an outbreak. The laboratory then searches for the source, comparing microbes from patients with swabs taken from the external environment and equipment. A match proves the transmission route.
Preventing nosocomial infections requires a multifaceted approach targeting the source, transmission routes, and the host.
- Architectural and planning stage: strict isolation of operating rooms, separation of "clean" and "dirty" flows, and proper air exchange.
- Sanitary and epidemiological stage: disinfection and sterilization measures, incidence surveillance.
- Specific prophylaxis: routine and emergency vaccination of patients and medical personnel.