Bacteremia

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Bacteremia

• MLAB 2434 Microbiology
• Keri Brophy-Martinez

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Definitions

• Pseudobacteremia
• False bacteremia
• Contamination of a blood culture during or after
  collection

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Definitions

• Bacteremia presence of bacteria in blood stream
• Some conditions have a period of bacteremia as
  part of the disease process (ex. Meningitis,
  endocarditis)
• Usually occurs due to a disruption of skin or
  mucosal barriers to bacterial invasion

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Classifications of Bacteremia

• Classified by Site of Origin
• Classified by Causative Agent
• Classified by Place of Acquisition
• Classified by Duration

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Classification by Site of Origin

• Primary Bacteremia
• Blood stream or endovascular bacterial invasion
  with no preceding or simultaneous site of
  infection with the same microorganism
• Secondary Bacteremia
• Isolation of a microorganism from blood as well
  as other site(s)
• Fever of Unknown Origin (FUO)
• Source unknown

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Classification by Causative Agent

• Gram positive bacteremia
• Gram negative bacteremia
• Anaerobic bacteremia
• Polymicrobial bacteremia

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Classification by Place of Acquisition

• Community-acquired
• Health-care acquired/Nosocomial
• Defined as occurring 72 hours post admission

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Classification by Duration

• Transient
• Comes and goes
• Usually occurs after a procedural manipulation
  (ex. Dental procedures)
• Intermittent
• Can occur from abscesses at some body site that
  is seeding the blood
• Continuous Bacteremia
• Organisms from an intravascular source that are
  consistently present in bloodstream

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Sepsis Septicemia

• Presence of active bacteria
• Results from continuous bacteremia
• Clinical signs and symptoms of bacterial invasion
  and toxin production
• Apply the SIRS criteria
• Systemic response to bacterial infection

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Bacteremia Complications

• Septic shock
• Results from bodys reactions to bacterial
  bi-products
• Endotoxins lipopolysaccharide
• Exotoxins
• Disrupts many body functions
• Hemodynamic changes, decreased tissue perfusion
  and compromised organ tissue function
• Mortality 40 to 50

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Bacteremia/Septicemia Risk Factors

• Immunocompromised patients
• Due to decrease in circulating neutrophils
• Increased use of invasive procedures indwelling
  devices
• Disrupts normal flora
• Age of patient
• Young defect in humoral immunity
• Old Decreased immune competency
• Administration of drug therapy
• Broad spectrum antibiotics decrease normal flora
• Increase in antimicrobial resistance

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Sources of Bacteremia

• Pericarditis and Peritonitis
• Pneumonias
• Pressure sores
• Prosthetic medical devices
• Total hip replacement
• Skeletal system
• Skin and soft tissue
• Urinary Tract Infections

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Clinical Signs and Symptoms

• Abrupt onset of chills, fever, or hypothermia and
  hypotension
• Prostration (exhaustion/weakness) and diaphoresis
  (perspiration)
• Tachypnea (rapid breathing) is an early sign of
  bacteremia
• Delirium, stupor, agitation
• Nausea, vomiting

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Clinical Signs and Symptoms (contd)

• Laboratory Values in Bacteremia
• Thrombocytopenia
• Leukocytosis or leukopenia
• Acidosis
• Abnormal liver functions
• Coagulopathy
• DIC
• Elevations in CRP, haptoglobin, fibrinogen, ESR,
  procalcitonin

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Specimen Collection

• Positive blood cultures
• Critical value
• Physician correlates finding to clinical picture
  to verify septicemia
• Best Practice
• Collect specimen immediately PRIOR to rise in
  temperature
• Collect PRIOR to antibiotic therapy

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Specimen Collection

• Aseptic collection procedure is critical
• Cleansing agents
• Tincture of iodine (1-2)
• Leave on skin for 30 seconds
• Povidine-iodine (10)
• Leave on skin 1.5 to 2 minutes
• Chlorhexidine/ChloraPrep
• Leave on skin for 30 seconds
• 2 chlorhexidine gluconate 70 isopropyl
  alcohol
• Cleansing Technique
• In concentric fashion, from inside to out
• After cleaning, wait 1.5-2 minutes
• Acceptable Contamination Rate
• 1-3

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Collection sites

• Preferred
• Peripheral venous
• Arterial sites
• Less common
• Central venous catheters
• Arterial lines

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Blood Collection Devices

• Traditional set
• Aerobic bottle
• Selects for aerobic facultative anaerobes
• Anaerobic bottle
• Selects for obligate anaerobes
• ARD bottle (Antibiotic Removal Device)
• Used when patient is on antibiotics prior to
  blood collection
• SPS Sodium polyanetholsulfonate

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Blood Collection Devices

• Anticoagulants
• SPS Sodium polyanetholsulfonate
• Function/Purpose
• Anticoagulant
• Neutralizes human serum
• Prevents phagocytosis
• Inactivates certain antimicrobial agents
• SAS(sodium amylosulfate)
• Similar to SPS, but less effective in
  neutralizing serum

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Specimen CollectionBlood Volume

• Ideal ratio of blood broth
• 15 to 110
• Dilution aids in preventing the bactericidal
  effect of WBCs complement
• Volume Recommendations by Age
• Younger than 10 years- 1 mL of blood for every
  year of life
• Over 10 years- 20 mL
• Short draw?
• Inoculate anaerobic bottle first

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Specimen CollectionFrequency of Collection

• Depends if bacteremia is transient, intermediate
  or continuous
• General guidelines
• Usually x2 from different body sites, when
  patient is spiking a fever
• Endocarditis
• 3 sets from 3 different sites within 1-2 hours of
  clinical presentation
• Fever of Unknown Origin (FUO)
• Initially 2 sets 24-36 hours later, obtain 2
  more

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Specimen CollectionFrequency of Collection

• If a catheter-related bloodstream infection is
  suspected
• One set drawn peripherally
• One set drawn via catheter

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Blood Culture Methods

• Conventional Broth Systems
• Aerobic broth contains soybean casein digest
  broth, tryptic or trypticase soy broth, Brucella
  agar or Columbia broth base
• Anaerobic broth is usually the same as aerobic
  with addition of 0.5 cysteine in an aerobic
  environment
• Must be subcultured and gram stained manually, at
  12, 24 and 48 hours
• Method not recommended due to risk of needlestick
  and contamination not cost effective

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Blood Culture Methods (contd)

• Biphasic Broth-Slide System
• Agar paddles attached to top of bottle
  includes CA, MAC, malt extract agars
• Incubate at 35 OC for 7 days
• Allows for blind subcultures
• Closed system

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Blood Culture Methods (contd)

• Lysis-Centrifugation Blood Culture Systems
  (Isolator)
• Used in the recovery of Fungus and AFB
• The Isolator is a special tube that contains
  saponin, a chemical that lyses cells and other
  anticoagulants
• Approximately 7.5-10 ml of blood is placed in the
  tube, then centrifuged to concentrate
  microorganisms sediment is subcultured to fungal
  and/or mycobacterial media

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Blood Culture Methods (contd)

• Automatic Blood Culture Systems
• BacTec 9000 Series
• Fluorescent light is used to detect changes in
  CO2 levels

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Bactec 9000 Series
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Automatic Blood Culture Systems (cont)

• ESP( Extra Sensing Power)
• Now VersaTREK
• Measures consumption/production of gases such as
  CO2 H2, N2 and O2 in the headspace of each bottle
• Detects a change in pressure

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Automatic Blood Culture Systems (cont)

• BacT-Alert
• Carbon dioxide production results in a pH change
• pH change results in color change detected by
  system as positive

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Blood Culture Workup

• Incubation times
• Routine aerobic/anaerobic
• 5-7 days
• Endocarditis
• 2 weeks
• Brucellosis/Fungemia/HACEK
• 21-28 days
• Reporting results
• Initial report is sent out at 24 hours
• Final report is sent out at 5-7 days for all no
  growth specimens

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Blood Culture Workup

• Positive Cultures
• Gram stain the bottle to determine the morphology
  of the organism present
• Call the results of the gram stain to the
  physician or nurse, including how many sets etc.,
  so that antibiotic therapy can be initiated
• Subculture to appropriate media
• Identify organism and perform sensitivity testing

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Blood Cultures Pathogens

• Staphylococcus aureus
• Streptococcus pneumoniae
• Haemophilus influenza
• Pseudomonas species
• Neisseria species
• Coagulase negative Staphylococcus species
  (immunocompromised)
• Group B Streptococcus (infants)
• Alpha hemolytic Streptococcus viridans group
• Gram negative rods
• Yeasts and molds
• Anaerobes

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Blood Cultures Contaminants

• Coagulase negative Staphylococcus
• Propionibacterium acnes
• Alpha hemolytic Streptococcus viridans group
• Bacillus species
• Diphtheroids
• Growth of multiple organism

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Treatment Prevention

• Treatment
• Empirical treatment, initially, with broad
  spectrum antibiotic
• Antisepsis therapy physiological support,
  anticoagulation agents, glucocorticoids
• Adjunctive measures draining fluids, removing
  catheters
• Prevention
• Vaccines S. pneumo, influenza, varicella

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References

• Broyles, M. (2013, June). A Closer Look at
  Sepsis. ADVANCE for Medical Laboratory
  Professionals, 25(5), 12-13.
• http//www.achats-publics.fr/Fournisseurs/BIOMERIE
  UX.htm http//www.bd.com/ds/productCenter/212536.a
  sp
• http//www.bd.com/ds/productCenter/445718.asp
• http//www.temple.edu/medicine/microbiology_lab.ht
  m
• Kiser, K. M., Payne, W. C., Taff, T. A. (2011).
  Clinical Laboratory Microbiology A Practical
  Approach . Upper Saddle River, NJ Pearson
  Education.
• Mahon, C. R., Lehman, D. C., Manuselis, G.
  (2011). Textbook of Diagnostic Microbiology (4th
  ed.). Maryland Heights, MO Saunders.