Bacteremia

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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 a known intravascular device, see “Catheter-related bloodstream infections; for those with surgical implants, see “Device-related infections.” For patients with fungemia, see “Management of systemic fungal infections.”

• Bacteremia: the presence of viable pathogen(s) in the bloodstream, with or without clinical signs of illness ^[2]
• Bloodstream infection (BSI): bacteremia or fungemia confirmed by a positive blood culture result ^[3][4]
  • Primary BSI: blood culture identifies an organism that is not related to an infection at another site AND
    • EITHER a noncommensal organism identified in ≥ 1 blood cultures
    • OR a noncommensal organism identified in one non-culture-based microbiologic test (e.g., PCR)
    • OR a commensal organism identified in ≥ 2 blood cultures collected on separate occasions in a patient with fever, chills, or hypotension
  • Secondary BSI ^[3]
    • 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 ^[5]
• 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 ^[4]

• Transient BSI: following minor procedures (e.g., IV cannulation, dental treatment, biopsy)
• Intermittent BSI
  • Spread from closed-space infections (e.g., intraabdominal abscess, soft tissue abscess)
  • Spread from focal infections (e.g., pneumonia, urinary tract infection, osteomyelitis)
• Persistent BSI: endovascular infection (e.g., endocarditis, vascular graft infection, infected thrombi, mycotic aneurysm)

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). ^[4]

Risk factors for BSI ^[6][7]

• Factors impairing the immune system
  • Congenital or acquired immunodeficiency
  • Diabetes mellitus
  • Major organ failures: cirrhosis, end-stage renal disease
  • Malignancy (esp. hematological malignancies)
  • Immunosuppressive or cytotoxic therapy
  • Neutropenia ^[8]
• Factors facilitating pathogen entry
  • Presence of indwelling lines and/or medical devices
  • Peripheral vascular disease with skin ulcers
  • Intravenous drug use ^[2]

Common pathogens and predisposing factors

In addition to general risk factors for BSI, certain conditions can predispose to infection with specific pathogens. See also “Risk factors for systemic fungal infection.”

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. ^[9]

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

• Systemic signs ^[6][8]
  • Fever (most common)
  • Chills and rigors ^[8]
  • Nonspecific signs of infection, e.g.:
    • Malaise
    • Reduced oral intake
    • Confusion
• Common infection site specific signs ^[8]
  • Presence of indwelling devices: e.g., central venous catheter (CVC), cardiac devices
    • Can manifest with erythema, swelling, or purulent discharge
    • See “Intravascular catheter-related blood stream infections.”
  • Respiratory: cough, shortness of breath; see “Pneumonia”
  • Cardiac: new murmur; see “Infective endocarditis”
  • Urinary: dysuria, flank pain; see “Urinary tract infection” and “Pyelonephritis”
  • Skin and soft tissue: erythema, signs of wound infection; see “Skin and soft tissue infections”
  • Musculoskeletal: back pain; see “Osteomyelitis”

Patients with bacteremia, particularly if elderly, can be oligosymptomatic in the early stages of their illness. ^[2]

The diagnosis of bloodstream infection requires blood cultures. ^[11]

• Indications for blood cultures: A selective approach is preferred; however, recommendations in the literature vary widely and there are no established guidelines. ^[12]
  • Estimate clinical pretest probability; e.g., bacteremia is more likely in patients with: ^[8]
    • Positive SIRS criteria
    • Fever PLUS chills
  • Consider using a clinical prediction score. ^[12][13]
  • Make a case-by-case decision under specialist guidance for patients with immune deficiency or a history of MDRO infection. ^[13]
• Interpretation of blood culture results
  • Correlate positive results to the clinical picture to assess their significance.
  • See “Positive blood culture interpretation” for pathogens most likely to represent true positive BSI vs. those that may be false positives.
• Acquisition technique: see “Blood cultures.”
• Additional investigations (e.g., CXR, urinalysis): Consider as needed to identify the source of infection if not clinically apparent; see “Septic workup.”

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. ^[8]

Approach ^[4][11][14]

Initial management of suspected BSI

• Acquire 2–4 sets of blood cultures to confirm BSI (gold standard). ^[15]
• For hemodynamically unstable patients and those at high risk of deterioration: Begin sepsis management.
  • Assess using ABCDE approach and resuscitate as needed, e.g., with immediate hemodynamic support.
  • Initiate empiric antibiotic therapy according to the suspected pathogen and underlying pathology; see “Antibiotic therapy for sepsis.”
• For clinically stable patients: The decision to treat empirically is made on a case-by-case basis.

When possible, obtain at least two sets of blood cultures prior to starting antimicrobial therapy. ^[11]

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. ^[16][17]
• 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.
• For fungemia, see “Management of systemic fungal infections.”
• Consult an infectious diseases specialist for guidance on antibiotic regimens and further management.

Follow-up blood cultures ^[14]

• Indications
  • Diagnostic confirmation, if there is growth of commensal organisms in a single blood culture in a symptomatic patient
  • Presence of risk factors for or suspected endovascular infection
  • Clinical evidence of persistent bacteremia and insufficient source control
• Timing: usually taken within 48 hours of initial cultures

Management of patients with medical devices

• Further diagnostic studies may be needed depending on the suspected source of infection, e.g.:
  • Intravascular catheter: cultures from catheter lumen and/or catheter tip ^[33]
  • Urinary catheter: urine culture after catheter removal or replacement ^[34]
  • Prosthetic joint: x-rays, arthrocentesis ^[35]
  • Vascular grafts: ultrasound, CTA, or MRA ^[5]
• Removal or replacement of device/line may be indicated after consulting with the appropriate specialty (e.g., infectious diseases, vascular surgery).
• See also “Intravascular catheter-related infection,” “Device-related infections,” “CAUTI,” and “Septic arthritis.”

• One-Minute Telegram 49-2022-3/3: A care bundle to reduce bloodstream infections in hemodialysis

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