Nosocomial infections are due to the combined effect of the pt's own flora and the presence of invasive devices in 25-50% of cases. Intensive education, “bundling” of evidence-based interventions, and use of checklists to facilitate adherence can reduce infection rates. Table 78-1 summarizes effective interventions to reduce the incidence of the more common nosocomial infections.

• Urinary tract infections: Thirty to forty percent of nosocomial infections are UTIs, contributing ~15% to prolongation of hospital stay with an attributable cost of ~$1300.
  • - Most nosocomial UTIs are associated with prior instrumentation or indwelling bladder catheterization. The 3-7% risk of infection for each day a catheter remains in place is due to the ascent of bacteria from the periurethral area or via intraluminal contamination of the catheter.
  • - In men, condom catheters may lessen the risk of UTI.
  • - The most common pathogens are Escherichia coli, nosocomial gram-negative bacilli, enterococci, and (particularly for pts in the ICU) Candida.
  • - For suspected infection in the setting of chronic catheterization, the catheter should be replaced and a freshly voided urine specimen obtained for culture to confirm actual infection as opposed to simple colonization of the catheter.
  • - As with all nosocomial infections, it is useful to repeat the culture to confirm the persistence of infection at the time therapy is initiated.
• Pneumonia: Accounting for 10-15% of nosocomial infections, pneumonia increases the duration of hospital stay by 10 days, accounts for ~$23,000 in extra costs, and is associated with more deaths than are infections at any other body site. Of pts using mechanical ventilation, 5-10% develop ventilator-associated events.
  • - Bacterial nosocomial pneumonia is caused by aspiration of endogenous or hospital-acquired oropharyngeal flora.
  • - Risk factors include events that increase colonization with potential pathogens, such as prior antibiotic use, contaminated ventilator equipment, or decreased gastric acidity; events that increase risk of aspiration, such as nasogastric or endotracheal intubation or decreased level of consciousness; and conditions that compromise host defense mechanisms in the lung, such as chronic obstructive pulmonary disease, extremes of age, or upper abdominal surgery.
  • - Etiologic organisms include community-acquired pathogens (e.g., Streptococcus pneumoniae, Haemophilus influenzae) early during hospitalization and Staphylococcus aureus, Pseudomonas aeruginosa, Klebsiella pneumoniae, Enterobacter, and Acinetobacter later in the hospital stay. In all, 20-40% of cases are polymicrobial.
  • - Diagnosis can be difficult, as clinical criteria (e.g., fever, leukocytosis, purulent secretions, and new or changing pulmonary infiltrates on CXR) have high sensitivity but low specificity.
    • An etiology should be sought by studies of lower respiratory tract samples protected from upper-tract contamination; quantitative cultures have diagnostic sensitivities in the range of 80%.
    • Febrile pts with nasogastric or nasotracheal tubes should also have sinusitis or otitis media ruled out.
• Surgical wound infections: Making up ~15-20% of nosocomial infections, surgical wound infections increase the length of hospital stay by 7-10 days and increase costs by $3000-$29,000.
  • - These infections often become evident after pts have left the hospital; thus, it is difficult to assess the true incidence.
  • - Risk factors include the pt's underlying conditions (e.g., diabetes mellitus or obesity) and age, inappropriate timing of antibiotic prophylaxis, the presence of drains, prolonged preoperative hospital stays, shaving of the operative site the day before surgery (rather than just before the procedure), long duration of surgery, and infection at remote sites.
  • - These infections are typically caused by the pt's endogenous or hospital-acquired flora.
    • S. aureus, coagulase-negative staphylococci, and enteric and anaerobic bacteria are the most common pathogens.
    • A group A streptococcal or clostridial etiology should be considered in rapidly progressing postoperative infections (manifesting within 24-48 h of a procedure).
  • - Clinical assessment of the surgical site may reveal obvious cellulitis or abscess formation; diagnosis of deeper infections requires a high index of suspicion and radiographic imaging.
  • - Treatment of postoperative wound infections requires source control (drainage or surgical excision of infected or necrotic material) and use of antibiotics aimed at the most likely or laboratory-confirmed pathogens.
• Intravascular device infections: Intravascular device-related infections cause 10-15% of nosocomial infections, increase the duration of hospital stay by 12 days, add $3700-$29,000 to hospital costs, and have an attributable mortality rate of 12-25%.
  • - Catheterization of the femoral vessels is associated with a higher risk of infection in adults.
    • These infections are largely due to the skin flora at the site of catheter insertion, with pathogens migrating extraluminally to the catheter tip.
    • Contamination of the infusate is rare.
    • Coagulase-negative staphylococci, S. aureus (≥50% methicillin-resistant isolates), enterococci, nosocomial gram-negative bacilli, and Candida are the pathogens most frequently associated with these bacteremias.
  • - Infection is suspected on the basis of the catheter site's appearance and/or the presence of fever or bacteremia without another source. The diagnosis is confirmed by isolation of the same bacteria from peripheral-blood cultures and from semiquantitative or quantitative cultures of samples from the vascular catheter tip.
  • - In addition to the initiation of appropriate antibiotic treatment, considerations include the level of risk for endocarditis (relatively high in pts with S. aureus bacteremia) and the decision regarding catheter removal, which is often necessary to cure infection.
    • The decision to remove a surgically implanted catheter should be based on the severity of the pt's illness, the strength of evidence that the device is infected, the presence of local or systemic complications, an assessment of the specific pathogens, and the pt's response to antimicrobial therapy if the catheter is initially retained.
    • If salvage of the catheter is attempted, the “antibiotic lock” technique (allowing a concentrated antibiotic solution to dwell in the catheter lumen along with systemic antibiotic administration) should be used.