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Critical Care Medicine

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Overview of Healthcare-Associated Infections

Defining Healthcare-Associated Infections

From Vincent JL et al: Textbook of critical care, ed 7, 2017

Bloodstream Infections

Blood stream infections are caused by a microbial pathogen found within the bloodstream that causes and inflammatory response with clinical, hemodynamic, and laboratory changes.

  • Primary BSI: when the central line that the patient has had for ≥ 48 hours is the only probable source of infection
  • Secondary BSI: when there is an underlying cause for the BSI (respiratory, genitourinary, etc) or any other obvious source of infection in the body
  • Hospital-acquired BSI: occurs after a patient has completed ≥ 48 hours of stay in the hospital
  • Community-acquired BSI: patient not in the hospital more than 48 hours before infection occurs


Central line-associated bloodstream infections (CLABSI) are defined by the National Healthcare Safety Network (NHSN) as:

A laboratory-confirmed BSI in a patient who had a central line within the 48 h period before the development of the BSI, or the BSI within 48 h of removal of a central venous catheter and which cannot be attributed to an infection unrelated to the catheter and that is not related to an infection at another site.

There is no minimum time for the catheter to have been in place in order for BSI to be CLABSI, but it must be within 48 hours of onset of infection. CLABSI confirmation requires both a positive blood culture and clinical evaluation of patient.


Catheter-associated urinary tract infections (CAUTI) are the most common urinary tract infections acquired in the hospital, with 75% of nosocomial UTI's associated with the urinary catheter. Since the most important risk factor for CAUTIs are prolonged use of urinary catheters, the best form of prevention is to limit their use to only appropriate indications and removed promptly when no longer needed.



Recommendations for Prevention of CR-BSI

From Vincent JL et al: Textbook of critical care, ed 7, 2017


Ventilator-associated pneumonia (VAP) is defined as pneumonia occurring in an individual on mechanical ventilation for more than 48 hours. Most VAPs are caused by bacterial pathogens, but it can also be caused by fungal pathogens, and rarely viral, such as during viral epidemics.

  • Early onset VAP: occurs within 4 days, usually caused by sensitive organisms
  • Late onset VAP: occurs on day 5 or after, usually associated with multidrug-resistant (MDR) pathogens and has a worse prognosis

The maximum risk of VAP is in the first few days of ICU admission and affects around 9-27% of all intubated patients. increasing with duration of mechanical ventilation. The risk is about 3% per day during first 5 days, 2% per day during fifth to tenth day and 1% per day thereafter. Most cases of VAP occur within 4 days of intubation. A large percentage of patients with ARDS will go on to develop VAP.

Common pathogens causing VAP
  • Gram negative aerobes
    • Pseudomonas aeruginosa
    • Klebsiella pneumoniae
    • Acinetobacter sp.
    • Escherichia coli
    • Enterobacter sp.
    • Serratia
    • Proteus sp.
  • Gram positive aerobes
    • Staphylococcus aureus
    • Streptococcus pneumoniae
  • Gram negative anaerobes
    • Bacteroides fragilis
  • Others
    • Candida albicans
      Influenza virus


Methicillin-resistant Staphylococcus aureus (MRSA) was first described in 1961 and outbreaks were first reported in the early 1960s. In the U.S. the prevalence of MRSA isolates in ICUs is around 60%.

HA-MRSA is defined as MRSA infection that occurs >48 hours following hospitalization or MRSA infection that occurs outside of the hospital within 12 months of exposure to health care (e.g., history of surgery, hospitalization, dialysis, or residence in a long-term care facility). The latter is referred to as Community-Onset HA-MRSA. HA-MRSA strains tend to have multidrug resistance and carry staphylococcal cassette chromosome (SCCmec) type II.

Healthcare-associated MRSA is often associated with severe invasive disease that can lead to bloodstream infections, skin and tissue infections, and pneumonia. HA-MRSA is most commonly transmitted to patients transiently through contaminated hands of healthcare workers or from contaminated environmental surfaces. Individuals (including healthcare workers, patients, and healthy asymptomatic individuals) colonized with MRSA serve as a reservoir for transmission.

Drugs Used to Treat MRSA Infections
Drug Dosage Renal dose adjustment Side effects Special note
Vancomycin LD25–30 mg/kg IV (especially in septic shock) 15–20 mg/kgof actual BW IV q8–12 h Required Red neck syndrome, DRESS, fever, thrombocytopenia, Neutropenia hearing lose, nephrotoxicity Individual dose >1gm/kg should be infused over1.5–2 h
Daily dose should be limited to 2gms/day
Trough level target 15–20 mcg/mL
Daptomycin 6 mg/kgTBW IV over 30 min q24 h Required myopathy, peripheral neuropathy, and eosinophilic pneumonia (Bonten et al. 1998; Snyder et al. 2008). Serial measurements of serum creatine kinase should be monitored at least weekly, and daptomycin should be discontinued in patients with symptomatic myopathy and creatine phosphokinase (CPK) ≥5 times the upper limit of normal (ULN) or in asymptomatic patients
With CPK ≥10 times the ULN
Do not use for primary pneumonia as inactive ny pulmonary surfactant
Non compatible with dextrose containing fluids
Teicoplanin LD 6 mg/kg IV 12 h for 3doses, then MD of 6 mg/kg IV 12 h.
Severe Infection
higher doses have been used LD 12 mg/kg iv 12 h 3 doses the MD 12
Required Hypersensitivity, fever, skin reaction marked thrombocytopenia, anemia and neutropenia
Red neck syndrome and nephrotoxicity lesser than vancomycin
Linezolid 600 mg/kg PO/IV q12h None Thrombocytopenia, anemia, lactic acidosis, peripheral neuropathy, serotonin toxicity, and ocular toxicity
Can reversibly inhibit monoamine oxidase

Enhanced efficacy against strains producing toxins such as Panton-valentine leukocidin, alpha-hemolysin, and toxic shock
Syndrome toxin 1

Table 22.2 Drugs used for MRSA infection, from Anand, R. (2020). Management of MRSA, VRE. In: Soneja, M., Khanna, P. (eds) Infectious Diseases in the Intensive Care Unit. Springer, Singapore.

Vancomycin-Resistant Enterococcus faecium (VREF)

Enterococci are gram-positive, facultative anaerobic organisms usually oval in shape and can be seen as single cells, pairs, or chains. Vancomycin-resistant Enterococcus (VRE) are enterococci that have become resistant to vancomycin and several antibiotics normally used to treat enterococcal infections.


The Clinical and Laboratory Standards Institute uses the following MIC definitions for vancomycin susceptibility and resistance in enterococci:

  1. Vancomycin susceptible: ≤4 mcg/ml
  2. Vancomycin resistant: ≥32 mcg/ml
  3. Vancomycin intermediate: 8 to 16 mcg/ml (vancomycin not recommended)

Enterococci are primarily found in the human digestive tract and female genital tract, where they make up a significant portion of the normal bacterial population in healthy people. Enterococci can cause urinary tract, wound, bloodstream, heart valve, and brain infections. In the great majority of cases, VRE infections occur in hospitalized patients who have compromised immune systems. Most cases of VRE are caused by the E. faecium strains that have acquired resistance when they came in contact with other bacteria and shared genetic information.

VRE is most commonly transmitted from one patient to another by health care workers whose hands have become contaminated inadvertently with feces or fluids of a person carrying the organism. VRE are not airborne but can survive on surfaces for several weeks.

Suggested Regimens for the Management of Infections Caused by Vancomycin- and Ampicillin-Resistant Enterococcus faecium

 Table 149-2: Harrison's Principles of Internal Medicine - Enterococcal Infections

Clostridioides difficile

C.difficile infection (CDI) is the most common cause of hospital-associated gastroenteritis. Patients with CDI often have prolonged hospital stays and it frequently causes large hospital outbreaks.

Severity of Infection
  • Mild: CDI with diarrhoea as the only symptom
  • Moderate: CDI with diarrhoea but without additional symptoms/signs meeting the definitions of severe or complicate CDI
  • Severe: CDI that presents with or develops during the course of illness with—hypoalbuminemia (<3 mg/dL) and either of the following - WBC > =15,000 cells/mm3 or abdominal tenderness without criteria of complicated disease
  • Severe: CDI that presents with or develops during the course of illness with—hypoalbuminemia (<3 mg/dL) and either of the following

    WBC > =15,000 cells/mm3 or abdominal tenderness without criteria of complicated disease Complicated: CDI that presents with or develops at least one of the following signs or symptoms

    • ICU admission
    • Hypotension with or without inotropes
    • Fever >38.5 Celsius
    • Ileus or significant abdominal distension
    • Mental status changes
    • WBC > = 35,000 or < 2000/mm3
    • serum lactate >2.2 mmol/L
    • Evidence of end organ failure

Treatment of CDI
  • Mild to Moderate CDI: Metronidazole 500 mg orally TDS for 10 days. If unable to take MN, vancomycin 125 mg orally four times a day for 10 days
  • Severe CDI: Vancomycin as above 125 mg QID for 10 days
  • Complicated CDI: Vancomycin orally 500 mg four times a day and Metronidazole 500 mg IV every 8H vancomycin 500 mg in 500 ml saline as enema rectally four times a day. Surgical consultation suggested.

Risk factors for CDI
  • Exposure to antibiotics (Cephalosporin, Clindamycin, Fluoroquinolone)
  • Exposure to organism
  • Comorbid conditions including Inflammatory Bowel Disease
  • GI tract surgery
  • Medications that reduce gastric acid (including PPI)
  • Nasogastric tube feeding
  • Organ transplantation
  • Chemotherapy
  • Chronic Kidney Disease
  • Immunodeficiency

HAI Prevention & Control