Bloodstream infections Flashcards
Bacteremia
When viable organisms are present in the blood. Threatens all organ systems. Continuous- caused by meningitis, osteomyelitis, osteoarthritis, pneumonia, typhoid fever, or peritonitis. Transient- after manipulation of mucous membranes or infected tissues
Septicemia (sepsis)
Systemic disease associated with pathogenic organisms or bacterial toxins in the blood stream: endotoxin or lipopolysaccharide (LPS)- gram negative organisms, or exotoxins- gram positive organisms
Septic shock
Acute circulatory failure caused by toxins of microorganisms. Causes multiple organ failure, acute respiratory distress, DIC (disseminated intravascular coagulation), tissue destruction, or death
Other laboratory findings with septic shock (4)
- Fever > 38C or hypothermia < 36 degrees.
- Leukocytosis (total WBC > 10,000 leukocytes/mm3
- Failure to thrive (neonates)
- Low grade fever
Predisposing factors for sepsis (7)
- Immunosuppression
- Underlying Disease – heart disease, rheumatic fever
- Medical devices – shunts, grafts, cardiac prostheses
- Surgery or other invasive procedures – cardiac catheterization
- Wide spread use of broad spectrum antimicrobial agents-colonization with antimicrobial resistant organisms or decreased normal flora
- Age
- Longer survival of debilitated and seriously ill patients
Phlebitis
infection/inflammation of the vein. Infections associated with intravascular catheters
Endarteritis
infection/inflammation of the inner lining of arteries. Infections associated with intravascular catheters
Carditis/myocarditis
inflammation of the heart muscle
Endocarditis
Infection of the heart, usually the valves. Vegetation – aggregates of fibrin and bacteria on the valves
Pericarditis
Infection of the region around the heart. Pericardial fluid – 15-20ml fluid between the heart and protective tissue covering
Symptoms of heart/blood vessel infections (3)
- Acute endocarditis
- Subacute bacterial endocarditis (SBE)
- Glomerulonephritis
Glomerulonephritis
Antibodies formed against M protein of group A Strep form and immune complexes. Immune complexes deposit in glomeruli causing renal pathology
Types of entry of organisms into the blood (7)
- Genitourinary- 25%
Respiratory- 20% - Abscess- 10%
- Surgical wound-5%
- Biliary Tract- 5%
- Miscellaneous- 10%
- Unknown origin- 25%
Automated system of processing blood cultures
Bottle noted as positive by detection methodology, technologist removes immediately for processing
Indications of a positive blood culture (4)
Indications of a positive blood culture:
a. Turbidity
b. Gas production
c. Hemolysis
d. Colony growth on blood layer
Immediate, preliminary workup of blood infections (5)
- Gram stain
- Report results, document call
- Plate correct media
- Setup preliminary testing (dependent upon gram stain)
- Setup PRELIMINARY antibiotics
Identification and susceptibility testing on subcultured organisms
Direct susceptibility tests from positive culture broth are NOT approved BUT may find some institution provide info. Direct tests:
a. Molecular - NAAT
b. Preliminary ID – API (if molecular ID not available)
c. Thermostable Dnase (if molecular ID not available for cocci in clusters)
Reporting results
Positive blood cultures are critical results and should be immediately verbally reported to the patient’s physician. Date, time, and name of the person accepting results should be documented. The clinician should be provided with all salient information, like gram stain morphology or the number of positive blood cultures. Verbal report should be followed with a written report. With negative cultures, preliminary reports are issued at 24 and again at 48 hr. Final report: No growth in 5 days
Contamination of specimens (5 prevalent species)
Contamination with normal flora should be less than 3%. Probable contamination if single positive culture growing:
1. Bacillus spp.
2. Corynebacterium spp.
3. Coagulase negative staphylococci (CoNS)
4. Cutibacterium acnes
5. Streptococcus spp.
Volume of blood collected
The most important variable for positive culture detection. As volume increases 2-30ml increase in pathogen recovery
Factors directly influencing culture results (5)
- Volume of blood collected
- Blood-to-broth ratio
- Skin disinfection is critical
- Prior antimicrobial therapy = false negatives
- Timing of collection is less important- multiple culture sets together OR over a 24 hr period
No advantage to 30 – 60 min apart.
Specimen type collected
Whole blood
Preparation of the collection site (2)
- Never draw specimen through indwelling catheter- UNLESS trying to R/O catheter associated infection
- Avoid contamination (normal flora). Contamination rate should be <3%, most hospitals 1 – 6%
Materials needed for blood draw (5)
- Sterile gloves
- 2% chlorhexidime gluconate and 70% isopropyl alcohol. Iodine is possible alternative, but not infrequently used
- Double needle collection set or vacutainer setup
- Aerobic and anaerobic blood culture bottles
- Tourniquet
Protocol for blood draws (3)
- Prepare blood culture bottles
- Prepare skin for venipuncture. Locate and palpate vein, always draw blood BELOW I.V. line, swab venipuncture with alcohol, swab the site with iodophor. Allow to remain for 30 sec-1 min
- Perform venipuncture. Inoculate aerobic and anaerobic blood culture bottles, label bottles accurately with: Patient info, TIME, SITE of collection
Number of specimens
Two bottle blood culture system- one aerobic and one anaerobic bottle inoculated/venipuncture. Recommendation – use both aerobic AND anaerobic bottle, inoculate aerobic bottle 1st. If only using aerobic bottles, use 2 per venipuncture site. Previous recommendations were use only aerobic bottles, anaerobic bottles provide no benefit….now thought this is incorrect.
Transport and storage of blood samples
Transport specimens to the laboratory within 2 hrs. Hold specimens at room temperature or 35C – NEVER refrigerate bottles. Lysis-centrifugation systems must be processed within 8hrs of collection
Pediatric specimen collection
The blood volume collected should be less than 1% of the patient’s blood volume.
Newborn to 1 year: .5-1.5 ml/tube
1-6 year olds: 1ml/year of age or 2 blood cultures
Children 30-80 pounds: 10 to 20 ml or 2 blood cultures
Adult specimen collection
20 to 30 mls can be collected per culture per venipuncture. 3 cultures can be collected over a 24 hour period
Catheter related blood stream infections- specimen collection
For a short term catheter: 2 sets collected from peripheral sites, remove the catheter and plate tip. For a long term central venous catheter: 2 sets can be collected at the same time. 1 peripheral, 1 line- same organism should be recovered from both
Septicemia specimen collection
2 cultures should be collected before antimicrobial therapy is begun. 10-20 mL sample should be collected from each arm
Bacterial endocarditis specimen collection
3-5 culture sets should be collected in total. When 3 sets are drawn, if they are negative at 24 hours obtain 2 additional sets. If they are still negative, consider an alternative diagnosis
Subacute infective endocarditis specimen collection
Establish diagnosis, obtain 3-5 sets of cultures, start antimicrobial therapy
Non-culture diagnosis of bacteremia
Standard methodology is NAAT (BioFire, Verigene, PCR). Latex agglutination and limulus amebocyte lysate assay are no longer used
Non-automated blood culture systems
Conventional – visual inspection of blood culture bottles and subculture within 24 hr. Held 7 days. Nutritious broth is used- can be for aerobic or anerobic organisms. Use an anticoagulant- Sodium Polyanethol Sulfonate (SPS). This process is labor intensive. Blind subcultures are necessary at day 5
Aerobic broth (3)
- Brain heart infusion (BHI)
- Trypticase soy (TSB) with 10% sucrose
- Columbia
Anaerobic broth (2)
- Thioglycollate
- Schaedler
Sodium Polyanethol Sulfonate(SPS)
An anticoagulant that neutralizes the bactericidal effect of serum and prevents phagocytosis. It inactivates Kanamycin, Gentamycin, Polymyxin B, Streptomycin. Can inhibit some species of bacteria
Which species does Sodium Polyanethol Sulfonate(SPS) inhibit? (4)
- Peptostreptococcus anaerobius
- GC
- N. meningitidis
- Gardnerella vaginalis
Lysis centrifugation method
Isolator system by Wampole. Blood draw, centrifuge, lyse, then plate on to solid media. Labor intensive process and an increased risk of contamination. Method for isolation:
Mycobacteria, Bartonella, or Histoplasma. Current BACTEC bottle methodology excellent
Manual (Conventional) Biphasic methods
Septichek- Broth and agar media inoculated
Principles for detection of microbial growth (8)
- Turbidity
- Colorimetry
- Fluorogenic compounds
- Laser imaging of growth in wells
- Fluorescent markers as probes for growing cells
- Bioluminescence
- Radioactive byproducts of microbial metabolism
- Change in pressure (manometric)
Continuous-Monitoring systems (3)
- Bactec 9240/9120: Measures CO2 production using fluorometry
- BacT/Alert (Organon/Teknika): Measures metabolic end product causing pH and color change on filter disk (colorimetry)
- bioMerieux Vital: Measures CO2 production, change in pH or redox potential by fluorometry.
Pericardial Fluid
Normally sterile body fluid between heart and protective tissue- may be accompanied by myocarditis
Pericardial fluid specimen collection and processing
Collect during surgery by aspiration. Concentrate specimen by centrifugation or filtration and plate immediately to enriched solid and broth media
Viral pathogens causing pericarditis
Usually viruses- enterovirus (coxsackieviruses)
Bacterial pathogens causing pericarditis (8)
- H. influenzae
- S. aureus
- Coagulase-negative Staph
- S. pneumoniae
- M. tuberculosis
- N. meningitis
- Member of the family Enterobacteriaceae and other GNR
- Anaerobes
Fungal pathogens causing pericarditis (3)
- Dimorphic fungi
- Opportunistic fungi
- Yeast
