Hospital-acquired infections (HAIs), also called nosocomial infections, are infections that are contracted 48 hours after hospitalization and that were not present or incubating at the time of 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 based 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). The preferred antibiotic therapy for an MDRO infection should be guided by the antibiogram, ideally in consultation with an infectious disease specialist.
This article provides an overview of the diagnosis and management of common HAIs.is covered separately. See also “ .”
- Hospital-acquired infection (nosocomial infection): an infection acquired after > 48 consecutive hours of hospitalization that was not present or incubating at admission
- Health care-associated infection (HCAI): an infection that develops 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)
Common causative pathogens 
|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|
|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, with particular importance to:
- Thorough chart review of recent (or current) hospitalization
- Assessment of all indwelling tubes and surgical sites for evidence of infection or inflammation
Pathogens (usually bacteria) that are resistant to ≥ 1 antimicrobial agent.
Risk factors 
- Prolonged hospitalization, especially in the ICU
- Prior antibiotic use
- Indwelling medical devices
- Exposure to other individuals with MDROs (e.g., long-term care facilities)
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) → 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)|