Nosocomial infection with example
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Nosocomial Infection
Definition
A nosocomial (hospital-acquired) infection is an infection originating in a patient while in a hospital or other healthcare facility. It represents a new disorder unrelated to the patient's primary condition - it was not present or incubating at the time of admission, nor is it the residual of an infection acquired during a previous admission. It also includes:
- Infections acquired in-hospital but appearing after discharge
- Infections occurring in hospital staff
The word "nosocomial" comes from Greek: nosos (disease) + komeo (to care for).
- Park's Textbook of Preventive and Social Medicine; - Sherris & Ryan's Medical Microbiology, 8th Ed., p. 112
Examples
| Type | Example | Common Pathogen(s) |
|---|---|---|
| Surgical Site Infection (SSI) | Wound infection post-appendectomy | S. aureus, E. coli |
| Urinary Tract Infection (UTI) | Catheter-associated UTI (CAUTI) | E. coli, Klebsiella, Candida |
| Pneumonia | Ventilator-associated pneumonia (VAP) | Pseudomonas, Acinetobacter |
| Bloodstream Infection | Central line-associated BSI (CLABSI) | Coagulase-negative Staph, MRSA |
| Hepatitis B | Post-transfusion or needle-stick hepatitis | Hepatitis B virus |
| Childbed fever (historical) | Puerperal endometritis in Semmelweis's era | Group A Streptococcus |
| GI Infection | Antibiotic-associated diarrhea | Clostridioides difficile |
| Environmental | Legionnaires' disease from hospital water | Legionella pneumophila |
- Park's Textbook of Preventive and Social Medicine (surgical wounds, hepatitis B, UTI listed as classic examples)
Sources of Nosocomial Infection
1. Hospital Personnel (Cross-infection)
Transmission from one patient to another ("cross-infection") most often occurs via inadequately washed hands of medical attendants. Sources include:
- Actively infected staff (e.g., a physician with a boil or "the flu")
- Asymptomatic carriers - nasal carriage of S. aureus or Group A Streptococcus is the most important
2. Medical Devices
Devices that breach normal defense barriers are a major route:
- Urinary catheters - bypass the urethral defense; CAUTI is the most common HAI
- IV/central venous catheters - access to bloodstream
- Mechanical ventilators/respirators - access to the lower respiratory tract
- Surgical implants - provide a surface for biofilm formation
Gram-negative rods (Pseudomonas, Acinetobacter, Enterobacteriaceae) thrive in moist device environments.
3. Environment
- Airborne pathogens: Mycobacterium tuberculosis (from infectious patients in wards)
- Water supply: Legionella pneumophila (aerosolized from contaminated hospital water, especially in immunocompromised patients post-cardiac surgery or bone marrow transplant)
Key Historical Example: Semmelweis and Childbed Fever
Ignaz Semmelweis (Vienna, 1840s) demonstrated the first major nosocomial infection control intervention. Maternal mortality from childbed fever (puerperal endometritis caused by Group A Streptococcus) was 11.4% in the physician-run unit vs. 2.7% in the midwife unit. After Semmelweis introduced chlorine handwashing, mortality in the physician unit dropped to 1.3% - equal to the midwife unit. Handwashing remains the single most important infection control measure today.
- Sherris & Ryan's Medical Microbiology, 8th Ed., p. 113
Risk Factors
- Advanced age
- Prolonged hospitalization
- Immunocompromising disease or therapy (e.g., chemotherapy, steroids, HIV/AIDS)
- Invasive devices (catheters, mechanical ventilation)
- Broad-spectrum antibiotic use (promotes resistant organisms)
- Surgical procedures
Common Causative Organisms
| Category | Organisms |
|---|---|
| Gram-positive bacteria | S. aureus (including MRSA), CoNS, Enterococcus (including VRE) |
| Gram-negative bacteria | E. coli, Klebsiella, Pseudomonas aeruginosa, Acinetobacter, Enterobacter |
| Anaerobes | Clostridioides difficile |
| Fungi | Candida spp. |
| Viruses | Hepatitis B/C, Norovirus, RSV |
Prevention
- Hand hygiene - the single most effective measure
- Aseptic technique for all invasive procedures
- Timely removal of catheters and lines
- Surgical site infection bundles (preop antibiotics, skin prep)
- Isolation precautions (contact, droplet, airborne) for known carriers
- Environmental cleaning and water system maintenance
- Antimicrobial stewardship to reduce resistance
Clinical significance: Nosocomial infections affect approximately 1 in 10 hospitalized patients globally, prolong hospital stay, increase costs, contribute to antimicrobial resistance, and cause significant morbidity and mortality - the majority of which are preventable with systematic infection control.
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