Hospital-acquired infections

Last updated: November 20, 2023

Summary

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 infections,” “Device-related infections,” and “Bacteremia.”

Definition

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]

Etiology

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

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
- Foreign bodies (e.g., catheters, intravenous catheters, endotracheal tubes) and invasive instruments
- Multiple interventional procedures (e.g., in patients with shock, major trauma, acute renal failure, coma)
- Mechanical ventilation
- Hemodialysis
Recent antibiotic use
Metabolic diseases (especially diabetes mellitus)
Immunosuppression

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]

Overview of the most common pathogens in HAIs ^[7]
Type of infection	Most common pathogens	Other causative pathogens
Surgical site infections	E. coli S. aureus	S. epidermidis Enterococcus spp. Enterobacter spp. P. aeruginosa Candida spp.
Nosocomial pneumonia	S. aureus P. aeruginosa	Bacteria Enterobacteriaceae (e.g., E. coli, Klebsiella species, Enterobacter species) H. influenzae S. pneumoniae MRSA Extended-spectrum beta-lactamase (ESBL)-producing Enterobacteriaceae A. baumannii Viruses ^[11] Rhinovirus Herpes simplex virus Cytomegalovirus Candida spp.
Nosocomial urinary tract infections	E. coli	Klebsiella spp. Enterococcus spp. P. mirabilis P. aeruginosa Enterobacter spp. Candida spp.
Bloodstream infections	S. aureus Coagulase-negative staphylococci (e.g., S. epidermidis)	Enterococcus spp. Klebsiella pneumoniae E. coli Candida spp.
Gastrointestinal infections	C. difficile	E. coli S. aureus P. aeruginosa Candida spp.

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

Overview of hospital-acquired infections ^[13]^[14]
Conditions	Risk factors	Diagnostic criteria ^[14]	Initial management steps
Conditions	Risk factors	Diagnostic criteria ^[14]	Initial management steps	Intravascular catheter-related bloodstream infection ^[15]	Immunosuppression Catheter-related risk factors and location Prolonged catheterization See also “Risk factors for CRBSI.”	Isolation of the same organism from ≥ 2 cultures obtained simultaneously from different sites See “Diagnostic criteria for CRBSI.”	Start empiric antibiotic therapy for CRBSI. Catheter removal if indications for intravascular catheter removal are met. See “Intravascular CRBSI” for details.
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	Start antibiotic therapy for complicated lower UTIs. Catheter removal or replacement For further management, see “Catheter-associated UTIs.”
Nosocomial pneumonia ^[17]^[18]	Longer hospital stays ^[17] Risk factors for aspiration Risk factors for antibiotic resistance	Hospital-acquired pneumonia (HAP): a clinical diagnosis of pneumonia, occurring > 48 hours after a patient is admitted to a hospital without evidence of disease at the time of admission Ventilator-associated pneumonia (VAP): a clinical diagnosis of pneumonia that occurs > 48 hours after the initiation of mechanical ventilation via either tracheostomy or intubation	HAP: Start empiric antibiotic therapy for hospital-acquired pneumonia. VAP: Start empiric antibiotic therapy for ventilator-associated pneumonia.
Surgical site infection (SSI) ^[14]^[19]^[20]	Patient factors Immunosuppression Infection prior to surgery Risk factors for impaired wound healing Factors that inhibit wound care Surgical factors Emergency surgery Long duration of surgery Bowel surgery	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	Source control (e.g., irrigation, debridement, drainage) ^[19] Empiric antibiotic therapy for SSI as needed
Clostridioides difficile infection ^[21]^[22]^[23]^[24]	Alterations in gut microbiota Recent antibiotic use ^[25]^[26] Inflammatory bowel disease Gastric acid suppression Patient factors Advanced age Immunosuppression	Diagnosis requires the following: ^[21]^[22]^[27] Typical clinical features Objective confirmation of infection	Discontinue precipitating antibiotics. Initiate isolation precautions (see “Secondary prevention of CDI”). Correct fluid and electrolyte imbalances. Administer antibiotic therapy for CDI. See “Treatment of C. difficile infection” for details.

Management

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
Diagnostics
- Routine laboratory studies for suspected infection, including:
  - CBC, ESR, CRP, procalcitonin
  - Blood cultures
  - Consider urinalysis.
- Additional directed workup as needed; examples include:
  - Cultures and/or PCR from the likely site(s) of infection
  - Imaging studies of the likely site(s) of infection
Management
- Management of sepsis
- Empiric or targeted antibiotic therapy of the underlying infection
- Consult infectious disease specialists for the management of MDRO infections.
- Determine the need for PPE and follow isolation precautions as needed.

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]

Multidrug-resistant organisms (MDROs)

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)

Resistance
- Forms a modified penicillin-binding protein (PBP) that inhibits binding of beta-lactam antibiotics, thereby decreasing their bactericidal effect.
- Modified PBPs are encoded by the mecA gene on the staphylococcal chromosome. ^[31]
Epidemiology: asymptomatic colonization of the nasal mucosa estimated to affect 0.5–5% of the population
Diseases: nosocomial and community-acquired infections
Measures
- Hygiene measures
  - Hand disinfection
  - Protective clothing (gown, mask)
  - Disinfection of patient rooms
- Patient isolation (if necessary, cohort isolation)
- MRSA eradication in asymptomatic carriers
  - Mupirocin nasal ointment
  - Antiseptic solution for skin/hair contamination (e.g., chlorhexidine)

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)

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)
Diseases
- Nosocomial urinary tract infections
- Health care-associated pneumonia
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) ^[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

Resistance: high natural resistance to antibiotics
Diseases
- Pneumonia
- Severely infected wounds
- Urinary tract infections
- Otitis externa (swimmer's ear)
- Keratitis

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]	All beta-lactam antibiotics (penicillins, cephalosporins, and carbapenems) Potential resistance to: Aminoglycosides Macrolides Lincosamides Quinolones		Vancomycin	Linezolid Daptomycin Tigecycline Ceftaroline Doxycycline Quinupristin/dalfopristin
Gram-positive	Vancomycin-resistant enterococci (VRE)	Vancomycin (possibly also teicoplanin) Potential resistance to: Macrolides Most penicillins Quinolones Aminoglycosides Tetracyclines		Linezolid	Quinupristin/dalfopristin Tigecycline Daptomycin
Gram-negative	ESBL pathogens (extended-spectrum β-lactamase)	Penicillins Cephalosporins	MDRGNB ^[37] Fluoroquinolones Carbapenems Third and fourth generation cephalosporins Broad-spectrum penicillins	MDRGNB: carbapenems	In case of resistance to all four groups, consider last resort antibiotics: Colistin Gentamicin Tigecycline
Gram-negative	Pseudomonas aeruginosa	Most penicillins First, second, and third generation cephalosporins Macrolides		MDRGNB Piperacillin PLUS tazobactam Certain third generation cephalosporins (e.g., ceftazidime) Carbapenems All options can potentially be combined with an aminoglycoside.	In case of resistance all four groups, give last resort antibiotics according to antibiogram: Colistin Polymyxin B

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