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.
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 
- 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) 
Risk factors 
- Age > 70 years
Lengthy hospital stays; pathogen transmission can occur via:
- Medical staff (e.g., insufficient disinfection of hands, clothing)
- Contact surfaces (e.g., equipment, furniture)
- Contaminated indoor air (e.g., via droplets)
- Iatrogenic: caused by a therapeutic or a diagnostic procedure
- Recent antibiotic use
- Metabolic diseases (especially diabetes mellitus)
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. 
Common causative pathogens 
|Overview of the most common pathogens in HAIs |
|Type of infection||Most common pathogens||Other causative pathogens|
|Surgical site infections|
|Nosocomial pneumonia|| |
|Nosocomial urinary tract infections|
Up to 20% of hospitalized patients are readmitted within 30 days of discharge. Monitor these patients closely for HAIs with drug-resistant organisms. 
|Overview of hospital-acquired infections |
|Conditions||Risk factors||Diagnostic criteria ||Initial management steps|
|Intravascular catheter-related bloodstream infection || || |
| Catheter-associated urinary tract infection |
| || |
|Nosocomial pneumonia |
Surgical site 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.
Medical history and examination focusing on:
- Thorough chart review of recent (or current) hospitalization
- Assessment of indwelling lines and tubes, implanted devices, and surgical sites for signs of infection or inflammation
In the emergency department, consider early implementation of measures (e.g., empiric isolation) in patients with suspected airborne infections or . 
Consider the antibiotics.  when prescribing
Pathogens (usually bacteria) that are resistant to ≥ 1 antimicrobial agent.
Risk factors for MRDO infection 
- Prolonged hospitalization, especially in the ICU
- Prior antibiotic use 
- Indwelling medical devices
- Exposure to other individuals with MDROs (e.g., in long-term care facilities)
- Prior history of MDRO colonization or infection
Methicillin-resistant Staphylococcus aureus (MRSA)
- Epidemiology: asymptomatic colonization of the nasal mucosa estimated to affect 0.5–5% of the population
- Diseases: nosocomial and community-acquired infections
Extended-spectrum beta-lactamase-producing bacteria (ESBL)
- Resistance: Bacteria produce beta-lactamases that have a broad spectrum and cleave penicillins, cephalosporins, and, in isolated cases, carbapenems.
- Pathogens: : particularly gram-negative bacteria (e.g., Enterobacteriaceae such as Klebsiella spp., Escherichia coli)
- Measures: isolation in separate rooms required
Vancomycin-resistant enterococci (VRE)
- Definition: bacterial strains of the genus Enterococcus that are resistant to vancomycin (e.g., E. faecalis, E. faecium)
- Resistance: : acquisition of van genes (e.g., through transposition of plasmid-encoded genes such as the vanA gene) → alteration of peptidoglycan synthesis pathway (e.g., due to change from the d-alanine-d-alanine amino acid sequence to d-alanine-d-lactate) → inhibition of vancomycin binding to peptidoglycan
Multidrug-resistant gram-negative bacteria (MDRGNB) 
- Definition: gram-negative pathogens that are resistant to at least three of the four main antibiotic classes
- Resistance: high natural resistance to antibiotics
- 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. 
- Combination therapy with multiple antibiotic agents may be needed.
- Antibiotic stewardship programs may require infectious disease approval for certain medications.
|Treatment of multiresistant pathogens|
|Pathogen||Resistance||First-line therapy||Alternative therapy|
|Vancomycin-resistant enterococci (VRE)|
|Gram-negative||( pathogensextended-spectrum β-lactamase)|
- One-Minute Telegram 87-2023-2/3: Breathe easier: a breakthrough in preventing ventilator-associated pneumonia
- One-Minute Telegram 49-2022-3/3: A care bundle to reduce bloodstream infections in hemodialysis
Interested in the newest medical research, distilled down to just one minute? Sign up for the One-Minute Telegram in “Tips and links” below.