Prevention of Hospital-Acquired Infections

Nosocomial pathogens have reservoirs, are transmitted by largely predictable routes, and require susceptible hosts-features that allow the implementation of monitoring and prevention strategies.

• Surveillance: Computerized algorithm-driven review of hospital databases is replacing manual review of microbiology laboratory results and surveys of nursing wards, but all these mechanisms keep track of infections acquired after hospital admission. Results of surveillance are expressed as rates and should include a denominator indicating the number of pts exposed to a specific risk (e.g., pts using a mechanical ventilator) or the number of intervention days (e.g., 1000 pt days on a ventilator).
• Prevention and control measures:Hand hygiene is the single most important measure to prevent cross-infection.
  • Health care workers' rates of adherence to hand-hygiene recommendations are abysmally low at <50%.
  • Other measures include identifying and eradicating reservoirs of infection and minimizing use of invasive procedures and catheters.
• Isolation techniques: Isolation of infectious pts is a standard component of infection control programs.
  • - Standard precautions include hand hygiene and use of gloves when there is a potential for contact with blood, other body fluids, nonintact skin, or mucous membranes during the care of all pts. In certain cases, masks, eye protection, and gowns are used as well.
  • - Transmission-based guidelines: Airborne, droplet, and contact precautions-for which personnel don (at a minimum) N95 respirators, surgical face masks, and gowns and gloves, respectively-are used to prevent transmission of disease from pts with contagious clinical syndromes. More than one precaution can be used for diseases that have more than one mode of transmission (e.g., contact and airborne isolation for varicella).

Nosocomial and Device-Related Infections

Nosocomial infections are due to the presence of invasive devices in 25-50% of cases. Intensive education, “bundling” of evidence-based interventions, use of checklists to facilitate adherence, and improvements in the design of these devices have reduced infection rates. Table 81-1 Examples of Selected Components of Evidence-Based Bundled Interventions to Prevent Common Health Care-Associated Infections and Other Adverse Eventsa summarizes effective interventions to reduce the incidence of the more common nosocomial infections.

• Urinary tract infections: UTIs represent ∼14% of nosocomial infections and have an attributable cost of ∼$900.
  • 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 24% of nosocomial infections, pneumonia increases the duration of hospital stay by 12-14 days, accounts for ∼$40,000 in extra costs, and is associated with more deaths than are infections at any other body site. Of pts using mechanical ventilation, ∼10% develop ventilator-associated events.
  • 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.
  • 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 ∼24% of nosocomial infections, surgical wound infections increase the length of hospital stay by up to 11 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).
  • 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 account for 10-15% of nosocomial infections, increase the duration of hospital stay by 7-15 days, add $31,000-$65,000 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 but can cause epidemic device-related bacteremias.
    • 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.

Epidemic and Emerging Problems

Although outbreaks and emerging pathogens often receive a great deal of press, they account for <5% of nosocomial infections.

• Influenza: The main components of infection control-vaccination of the general public and health care workers, early use of antiviral agents for control of outbreaks, and adherence to surveillance and droplet precautions for symptomatic pts-have been effective in controlling influenza, including the 2009 H1N1 pandemic.
• Nosocomial diarrhea: Rates of health care-associated diarrhea have been increasing in recent years.
  • Rates of infection with Clostridium difficile-particularly the more virulent NAP1/BI/027 strain-are increasing, especially among older pts. Important infection-control components include judicious use of antibiotics (particularly fluoroquinolones); heightened suspicion in cases with atypical presentations; enhanced disinfection of isolation rooms; and early diagnosis, treatment, and implementation of contact precautions.
  • Outbreaks of norovirus infection should be suspected in bacterial culture-negative diarrheal syndromes in which nausea and vomiting are prominent aspects. Contact precautions may need to be augmented by environmental cleaning and active exclusion of ill staff and visitors, who often represent index cases.
• Chickenpox: Routine vaccination of children and VZV-susceptible employees has made nosocomial spread less common.
• Tuberculosis: Prompt recognition and isolation of cases, use of negative-pressure private rooms with 100% exhaust and at least 6-12 air changes per hour, use of approved N95 respirators, and follow-up serologic or skin testing of susceptible, exposed personnel are required.
• Group A streptococcal infections: One or two nosocomial cases, usually involving surgical wounds and the presence of an asymptomatic carrier in the operating room, should trigger an investigation. Health care workers linked to nosocomial transmission of group A streptococci should not be permitted to return to pt care settings until eradication of carriage via antimicrobial therapy has been documented.
• Fungal infections: Hospital renovations and disturbance of dusty surfaces can cause fungal spores to become airborne. Routine surveillance of neutropenic pts for infections with filamentous fungi (e.g., Aspergillus, Fusarium) helps determine whether there are extensive environmental risks. Candida auris is an emerging multidrug-resistant pathogen that causes invasive health care-associated infections.
• Legionellosis: If nosocomial cases are detected, environmental samples (e.g., tap water, water used in decorative fountains) should be cultured; eradication measures should be pursued if typing of clinical and environmental isolates reveals a correlation.
• Antibiotic-resistant bacterial infection: Close laboratory surveillance, strict infection-control practices, and aggressive antibiotic-control policies are the cornerstones of resistance-control efforts.
  • Molecular typing can help distinguish an outbreak of a single isolate (which necessitates an emphasis on hand hygiene and an evaluation of common-source exposures) from a polyclonal outbreak (which necessitates re-emphasis on antibiotic prudence and device bundles).
  • Organisms that raise concerns include methicillin-resistant S. aureus, gram-negative organisms that produce carbapenemases and/or extended-spectrum β-lactamases, pan-resistant strains of Acinetobacter, and vancomycin-resistant enterococci.
• Bioterrorism preparedness: Education, effective systems of internal and external communication, and risk assessment capabilities are key features.