Bacteremia

Last updated: March 17, 2022

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Bacteremia is a condition characterized by the presence of viable pathogens in the bloodstream. Bacteremia can occur transiently in healthy individuals (e.g., after tooth brushing) or as the result of a localized infection spreading to the bloodstream. Risk factors for bacteremia include conditions that cause immunosuppression (e.g., diabetes mellitus, malignancy) and those that facilitate pathogen entry or adhesion (e.g., presence of intravascular catheters, prosthetic material). Diagnosis is confirmed with blood cultures to identify the causative pathogen and its antimicrobial resistance pattern. If blood cultures are positive, bacteremia is considered a bloodstream infection (BSI). BSI most commonly manifests with nonspecific symptoms of infection, such as fever, or clinical features related to the site of the primary infection (e.g., urinary symptoms in urinary tract infection). Further investigations may be required depending on the suspected source of the BSI. Treatment includes antibiotic therapy and source control (e.g., abscess drainage, change/removal of prosthetic material). Empiric broad-spectrum antibiotic therapy is indicated in acutely unwell patients and can be deescalated according to culture results.

For patients with bacteremia who are hemodynamically compromised or have other signs of severe systemic infection, see “Sepsis.” For details on technique of blood culture acquisition, see “Blood cultures.” For patients with bacteremia and known intravascular device, see “Catheter-related bloodstream infections.”

  • Bacteremia: the presence of viable pathogen(s) in the bloodstream, with or without clinical signs of illness [1]
  • Bloodstream infection (BSI): bacteremia or fungemia confirmed by a positive blood culture result [2][3]
    • Primary BSI: blood culture identifies an organism that is not related to an infection at another site AND
    • Secondary BSI [2]
      • A BSI secondary to an infection at another site (e.g., UTI, pneumonia)
      • Confirmed by identifying the same organism(s) on cultures from blood and the suspected primary source of infection
  • Endovascular infection: infection that involves either the arterial or venous vasculature (native vessels or implanted devices); associated with sustained bacteremia [4]
  • Sepsis: a severe, life-threatening condition that results from a dysregulation of the patient's response to an infection, causing tissue and organ damage and subsequent organ dysfunction

Sources of infection [3]

Transient bacteremia with no clinical significance can occur in otherwise healthy individuals after manipulation of a nonsterile site (e.g., manipulation of the oral cavity during tooth brushing). [3]

Risk factors for BSI [5][6]

Common pathogens and predisposing factors

In addition to general risk factors for BSI, certain conditions can predispose to infection with specific pathogens.

Gram-negative bacteria such as Enterobacteriaceae cause nearly half of all cases of community-associated BSIs and one third of cases of healthcare-associated BSIs. [8]

Clinical features depend on the suspected source for bacteremia; affected individuals can also be asymptomatic and bacteremia can resolve spontaneously.

Patients with bacteremia, particularly if elderly, can be oligosymptomatic in the early stages of their illness. [1]

The diagnosis of bloodstream infection requires blood cultures. [10]

Obtaining blood cultures inappropriately can cause harm due to overtreatment. Avoid routinely ordering blood cultures for adult patients with isolated fever or leukocytosis unless they are immunosuppressed or infective endocarditis is suspected. [7]

Approach [3][10][13]

Initial management of suspected BSI

When possible, obtain at least two sets of blood cultures prior to starting antimicrobial therapy. [10]

Further management

  • Perform further diagnostics to investigate the source of bacteremia: e.g., consider echocardiography to support a diagnosis of endocarditis.
  • Initiate source control, for septic patients ideally within 6–12 hours of diagnosis. [15][16]
  • Once the causative pathogen is identified:
    • Deescalate antibiotics to pathogen-specific agents.
    • Further investigations (e.g., imaging for intraabdominal pathology) or longer treatment courses may be required.

Consult an infectious diseases specialist early regarding management with antimicrobial therapy and source control.

Management of common pathogens

Targeted treatment should always be guided by susceptibility testing results. Treatment duration is highly variable and depends on the source and causative agent of infection. Consult an infectious diseases specialist for guidance on antibiotic regimens and further management.

Management of common BSI pathogens [17][18]
Microorganism Suggested antibiotic regimens and considerations

Methicillin-susceptible S. aureus (MSSA) [19][20]

Methicillin-resistant S. aureus (MRSA) [21]

Staphylococcus epidermidis [23]

Streptococci spp. [18][24]
Enterobacteriaceae
Pseudomonas aeruginosa [27][28]
  • Highly dependent on mechanisms of resistance
  • Commonly used options include monotherapy with meropenem OR imipenem-cilastatin . [18][26]
Enterococcus spp.

Follow-up blood cultures [13]

Management of patients with medical devices

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