A. Definitions

1. Usually defined as infection acquired >48-72 hours after hospital admission
2. Often called hospital acquired (versus community acquired) infection
3. Can occur after admission to any healthcare facility
4. Often associated with drug resistant pathogens
5. Latin word for "hospital" is nosocomium (noso=disease, komein=to care for)
6. Overall occurs in ~20% of intensive care unit (ICU) patients

B. Pathogenesis

1. Reduced host defenses and colonization by (potentially) pathogenic organisms
2. Reduced Host Defenses
   1. Chronic concurrent disease process leads to immunosuppression
   2. "Immunoparalysis" mediated by high levels of TNF receptors, IL10, IL1 receptor antagonist
   3. Immunosuppressive drugs
3. Bacterial Colonization
   1. Strongly associated with hospital stay
   2. Most strongly associated with reduced host defenses
   3. Presence of invasive devices providing nidus for infection
   4. Microperforations of gastrointestinal (GI) tract
   5. Chronic and broad-spectrum antibiotics lead to reduction in patient's normal flora
   6. Direct contact from healthcare personnel spreading between patients
   7. Airborne infections include Mycobacterium tuberculosis and some viral infections
   8. Main reservoirs for colonizers are oropharynx, GI tract, urinary tract
4. Main Pathogens
   1. Skin: Staphylococcus aureus (~30%), Staph epidermidus (~20%)
   2. Pseudomonas (~30%)
   3. Escherichia coli (~15%)
   4. Enterococci (~10%)
   5. Candida and other yeasts (~15%)
   6. Acinetobacter (~10%)
   7. Klebsiella (~8%)
   8. Enterobacter
   9. Serratia
5. Antibacterial Resistance
   1. Methicillin resistant Staph aureus most common (MRSA)
   2. Vancomycin resistant Enterococcus (VREF)
   3. Pseudomonas resistant to quinolones or 3rd generation cephalosporins
   4. Pseudomonas resistant to imipenem
   5. Klebsiella resistant to 3rd generation cephalosporins
   6. E. coli resistant to 3rd generation cephalosporins

C. Predisposing Factors [1]

1. Underlying Chronic Disease
   1. Malnutrition
   2. Alcoholism
   3. Smoking
   4. Chronic lung disease
   5. Diabetes
2. Acute Disease Processes
   1. Surgery
   2. Trauma
   3. Burns
3. Invasive Procedures
   1. Endotracheal or nasal intubation
   2. Central venous catheterization
   3. Extracorporeal renal support
   4. Surgical drains
   5. Nasogastric tube (mainly iatrogenic sinusitis)
   6. Tracheostomy
   7. Urinary catheter
4. Treatment Associated Predisposing Factors
   1. Immunosuppressive agents, most commonly glucocorticoids
   2. Blood transfusions
   3. Antimicrobial therapy
   4. Recumbent position
   5. Parenteral nutrition
   6. Stress ulcer prophylaxis with gastric acid reduction

D. General Prevention

1. Hand-hygiene is critically important, particularly in ICU
   1. Ring-wearing can reduce effectiveness of hand-hygiene
   2. Use of antiseptic, alcohol-based solutions more effective than soap and water
2. Surveillance for ventilator associated pneumonia
3. Antibiotic Selection
   1. Reduced use of broad-spectrum antibiotics
   2. Reduced use of vancomycin
   3. Cycling of antibiotics
4. Pharmacologic Prevention of Catheter Related Infections [2,3]
   1. Chlorhexidine gluconate cleansing of skin prior to placement of catheter
   2. Use of antibacterial or antiseptic impregnated catheters
   3. Skin preparation with alcoholic chlorhexidine is more efficacious than aqueous providone-iodine in preventing blood culture contamination [2]
5. Antibiotic coated urinary catheters under investigation

References

1. Vincent JL. 2003. Lancet. 361(9374):2068
2. Chaiyakunapruk N, Veenstra DL, Lipsky BA, Saint S. 2002. Ann Intern Med. 136(11):792
3. McGee DC and Gould MK. 2003. NEJM. 348(12):1123