blood-culture-final by lanyuehua

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									•   Only 5-15% of blood cultures are (+) in febrile
    patients.

A. Types of bacteremia:
    Extravascular: via the lymphatic's.
    Intravascular: i.e. CVC infections.

B. Types of bacteremia:
    Transient: Disruption of mucosal surfaces (dental
     or surgical procedures).
    Intermittent: Associated with abscesses.
    Continuous: Infective endocarditis.
          Bacteremia: Pathogens

•   S. Aureus
•   S. Pyogenes
•   S. Pneumoniae
•   H. Influenzae
•   Enterobacteriaceae
•   Bacteroides
•   Pseudomonas Aeruginosa
•   Candida species
       Bacteremia: Contaminants

• Coagulase (-) Staphylococci.
• Corynebacterium species.
• Bacillus species.
• If multiple isolated from separate sites are
  obtained, the organisms could be pathogenic.
• Viridans Streptococci can be a contaminant.
Occurrence of False Positive Blood
        Cultures (Trash)
                      True (%) Trash (%)
S. aureus               87        6
Coag negative staph     12        82
Enterococcus            70        16
Diphtheroids             2        96
C. perfringens          23        77
C. albicans             90
                  Methods
• Two blood cultures for separate venipuncture
  sites is adequate.
• Three sets of blood.
• At least 10ml/ venipuncture.
• Blood culture > 5ml blood: 92% yield
• Blood culture < 5 ml blood: 69% yield

Note: Diagnostic yield increased by 3% for every
 1 ml of blood drawn
                Interpretation
• Organisms isolated > 72 hours are often
  contaminants.*

• A single blood cultures with coagulase (-)
  staphylococci is often a contaminant.**

• A single (+) blood cultures with S. Aureus, gm (-)
  bacillie or candida is always a pathogen and
  requires therapy.

• The patient does not have leukocytosis or a left
  shift (false-positive blood cultures).
                    Aim of the test
• Diagnosis of bacteremia by
    Aerobic and anaerobic cultivation of the blood,
    With identification&
    Susceptibility test of the isolated organism (s).

   • Pediatrics: only aerobic.*

• Blood culture should be made for cases with :
• suspected septicemia, endocarditis, and bacteremia secondary to
  localized infections (pneumonia, intraabdominal abscesses,
  pyelonephritis, epiglottitis, meningitis).
Aerobic/Anaerobic Blood Culture
            Bottles
    Criteria of specimen rejection
• Blood collected in tubes or bottles other than
  aerobic and anaerobic blood culture bottles.

• If the information on the label does not match
  that of the request form.

• Specimens for anaerobic blood culture received
  in aerobic bottles or vice versa.
Pathogens
                Patient preparing
• The major difficulty in interpretation of blood cultures
  is potential contamination by skin microbiota.

• So: careful attention to the details of skin preparation
  and antisepsis prior to collection of the specimen.
         Obtaining Blood Culture
• Locate the vein (usually anticubital fossa)
• Attention to IV line.
• Prep kit
   • Alcohol 5 sec. Dry 30-60 sec
   • Tincture of Iodine-center to periphery. Dry 45-60 sec
• Remove caps, clean with alcohol
• Put on gloves
• Without palpating, draw 20 ml and put 10 in anaerobic and 10
  in aerobic bottle.
• Dispose of syringe in sharps container.
• Label bottles and send to lab.
Set 1 = L. antecubital fossa at 0 minutes
Set 2 = R. antecubital fossa at 30 minutes
Set 3 = L. or R. antecubital fossa at 90 minutes.

Best time for sample collection: during fever spike\chills.


1st sample: 90% detection.
Quantity of specimen
                   Method
• Blood is injected to both aerobic and anaerobic
  bottles and incubated for up to 10 days at 37 C.
• Discard as negative after the 10 days
• During the incubation period, a gram stain and
  subculture onto appropriate media should be
  done.
Interpretation of Positive Blood Cultures
• Virtually any organism, including normal microbiota, can
  cause bacteremia.

• A negative culture result does not necessarily rule out
  bacteremia;
    false-negative results occur when pathogens fail to grow.

• A positive culture result does not necessarily indicate
  bacteremia;
    false-positive results occur when contaminants grow.
• Gram-negative bacilli, anaerobes, and fungi should
  be considered pathogens until proven otherwise.

• The most difficult interpretation problem is to
  determine whether an organism that is usually
  considered normal skin microbiota is a true
  pathogen.

								
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