Hospital-acquired infections

Last updated: May 20, 2022

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Hospital-acquired infections (HAIs), also called health care-associated infections (HCAIs) and nosocomial infections, are infections contracted in a hospital or other health care facility that were not present or incubating at the time of admission. Symptoms and/or signs of an HAI typically manifest 48 hours or more after admission. HAIs are transmitted through patient exposure to health care workers, other patients, hospital equipment, or interventional procedures. The most common types of HAIs include intravascular catheter-related bloodstream infection (CRBSI), catheter-related urinary tract infection (CAUTI), hospital-acquired pneumonia, ventilator-associated pneumonia, surgical site infection (SSI), and Clostridioides difficile infection (CDI). The most common causative pathogens differ depending on the site of infection (e.g., gastrointestinal tract, urinary tract, lungs, skin). An increasing number of HAIs are caused by multidrug-resistant organisms (MDROs). Common MDROs include methicillin-resistant Staphylococcus aureus (MRSA), extended-spectrum beta-lactamase-producing bacteria (ESBL), and vancomycin-resistant enterococci (VRE). Empiric antibiotic therapy for an MDRO infection should be guided by the local antibiogram, preferably in consultation with an infectious disease specialist.

This article provides an overview of the diagnosis and management of common HAIs. Prevention of nosocomial infections is covered separately. See also “Intravascular catheter-related bloodstream infection” and “Bacteremia.”

The following terms are often used interchangeably:

  • Hospital-acquired infection (nosocomial infection): an infection acquired in a hospital or another inpatient health care facility that was not present or incubating at the time of admission [1]
  • Health care-associated infection (HCAI): an infection acquired after receiving health care in any setting (including a hospital, long-term care facility, nursing home, ambulatory care clinic, home care, or surgical intervention) [2][3]

Risk factors [4][5][6][7]

Admission through the emergency department is associated with an increased risk of hospital-acquired pneumonia, as airborne pathogens are easily transmitted in crowded health care settings. [8][9][10]

Common causative pathogens [7]

Up to 20% of hospitalized patients are readmitted within 30 days of discharge. Monitor these patients closely for HAIs with drug-resistant organisms. [12]

Overview of hospital-acquired infections [13][14]
Conditions Risk factors Diagnostic criteria [14] Initial management steps
Intravascular catheter-related bloodstream infection [15]
Catheter-associated urinary tract infection
(CAUTI) [16]
  • Prolonged urinary catheterization (suprapubic, urethral, or condom)
  • Symptomatic culture-proven infection of the urinary tract system [16]
  • AND a urinary catheter in place for > 48 consecutive hours OR within 48 hours after removal of a urinary catheter
  • AND and no other source of infection
Nosocomial pneumonia [17][18]
Surgical site infection
(SSI)
[14][19][20]
  • An infection of the incision, organ, or space involved in a preceding surgical procedure [14][20]
  • Onset of symptoms postoperatively: [14]
    • Superficial incisional infections: within 30 days
    • Deep incisional, organ, and space infections: within 30–90 days
Clostridioides difficile infection [21][22][23][24]
  • Diagnosis requires the following: [21][22][27]
    • Typical clinical features
    • Objective confirmation of infection

Consider HAIs in patients who have recently been hospitalized or undergone a medical intervention and present with new-onset infectious symptoms (e.g., fever, cough, dysuria, pus, diarrhea) and/or unexplained clinical deterioration (e.g., hypotension, increased ventilator support, altered mental status). The approach to management may vary depending on the site of infection and is covered in detail in dedicated articles. The general approach to a suspected HAI is briefly described here.

In the emergency department, consider early implementation of infection prevention and control measures (e.g., empiric isolation) in patients with suspected airborne infections or risk factors for MDRO colonization. [9][28]

Consider the risk of MDRO colonization when prescribing antibiotics. [8]

Definition [29]

Pathogens (usually bacteria) that are resistant to ≥ 1 antimicrobial agent.

Risk factors for MRDO infection [29]

  • Prolonged hospitalization, especially in the ICU
  • Prior antibiotic use [30]
  • Indwelling medical devices
  • Exposure to other individuals with MDROs (e.g., in long-term care facilities)
  • Prior history of MDRO colonization or infection

Common pathogens

Methicillin-resistant Staphylococcus aureus (MRSA)

The resistance mechanism of MRSA relies on modified PBPs, not the formation of beta-lactamase. Every case of MRSA (symptomatic or asymptomatic) requires treatment.

Extended-spectrum beta-lactamase-producing bacteria (ESBL)

Vancomycin-resistant enterococci (VRE)

Multidrug-resistant gram-negative bacteria (MDRGNB) [32]

  • Definition: gram-negative pathogens that are resistant to at least three of the four main antibiotic classes
  • Measures
    • Suspected cases: no isolation
    • Confirmed cases
      • Basic hygiene measures in low-risk areas are sufficient.
      • Isolation in risk areas (e.g., ICU, neonatology, hematology-oncology)

Pseudomonas aeruginosa

Management [29][33][34]

  • Management of infections with MDROs is often complicated by limited antibiotic options.
  • Select antibiotic agents based on the antibiogram, preferably in consultation with an infectious disease specialist.
  • Antibiotics to which the MDRO has some resistance may still be used but at higher doses and/or increased frequency. [35]
  • Combination therapy with multiple antibiotic agents may be needed.
  • Antibiotic stewardship programs may require infectious disease approval for certain medications.

Antibiotic regimens for the same pathogen may differ based on the source of infection and the severity of the disease.

Treatment of multiresistant pathogens
Pathogen Resistance First-line therapy Alternative therapy
Gram-positive MRSA [36]
Vancomycin-resistant enterococci (VRE)
Gram-negative ESBL pathogens (extended-spectrum β-lactamase)
Pseudomonas aeruginosa

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