• Clinical science

Nosocomial infections (Hospital-acquired infections)


Nosocomial infections, also known as hospital-acquired infections, are newly acquired infections that are contracted within a hospital environment. Transmission usually occurs via healthcare workers, patients, hospital equipment, or interventional procedures. The most common sites of infection are the bloodstream, lungs, urinary tract, and surgical wounds. Though any bacteria may cause a nosocomial infection, there is an increasing incidence of multidrug-resistant pathogens (MDR) causing hospital-acquired infections. This rise can be explained by indiscriminate use of antibiotics and lacking hygiene measures, especially among medical staff. Commonly seen multidrug-resistant pathogens include methicillin-resistant Staphylococcus aureus (MRSA), extended-spectrum beta-lactamase-producing bacteria (ESBL), and vancomycin-resistant enterococci (VRE). The choice of antibiotic for treating infections with these pathogens is based on the individual resistance profile and often requires additional strict isolation methods for the patient.


  • Nosocomial infections are defined as infections acquired after hospitalization and occur within 48 hours of hospital admission, 3 days of discharge or 30 days of an operation. [1]
  • At admission, these infections are not present or incubating.


Common causative pathogens [2]

Overview of the most common causative pathogens
Type of infection Most common pathogens Other causative pathogens
Surgical site infections
Nosocomial pneumonia
Nosocomial urinary tract infections
Bloodstream infections

Risk factors [3][2][1]

  • Age > 70 years
  • Lengthy hospital stays → ↑ risk of infection
    • Medical staff (e.g., insufficient disinfection of hands, clothing)
    • Contact surfaces (e.g., equipment, furniture)
    • Indoor air (e.g., via contaminated by droplets from infected patients, staff, procedures like bronchoscopy)
  • Iatrogenic: caused by treatment or a diagnostic procedure
  • Prior antibiotic use
  • Metabolic diseases (especially diabetes mellitus)
  • Immunosuppression

Overview of multiresistant 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) [5]

  • 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 normal areas sufficient
      • Isolation in risk areas (e.g., intensive care, neonatology, hematology-oncology)

Pseudomonas aeruginosa

Treatment of multiresistant pathogens

Treatment of multiresistant pathogens [6]
Pathogen Resistance First-line therapy Alternative therapy
Vancomycin-resistant enterococci (VRE)
ESBL pathogens (extended-spectrum β-lactamase)
Pseudomonas aeruginosa

Intravascular catheter related infections

  • Definition
    • Catheter-related bloodstream infection (CRBSI) is a bloodstream infection attributed to an intravascular catheter.
  • Risk factors
  • Etiology: the most common pathogens are:
  • Clinical features
    • Fever
    • Hemodynamic instability
    • Swelling, pain, redness, and purulence at catheter insertion sites
    • Altered mental status
  • Diagnosis
    • Approach: Catheter-related blood stream infection should be suspected in patients presenting with septic features 48 hours after insertion of the catheter.
    • Blood culture: samples should be collected prior to initiation of antibiotics
      • Collect two blood samples from a peripheral venous site (ideal)
      • Collect one blood sample from a peripheral venous site and culture the catheter tip
      • Collect one blood sample from a peripheral venous site and another sample from a catheter hub
  • Definitive diagnosis if:
    • The same organism grows from the catheter tip (> 15 colony-forming units [CFUs]/plate using semiquantitative culture or 102 CFU using quantitative culture) and percutaneous blood sample.
    • The same organism grows from the percutaneous blood sample and catheter hub blood sample, with a 3-fold colony count in the latter.
    • The same organism grows from the percutaneous blood sample and catheter hub blood sample, with the microbe being detected 2 hours earlier in the latter.
  • Treatment
  • Start empiric treatment
  • Prevention: See ”Prevention of intravascular catheter-related infections.”

References: [8][9][10]