2. 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

3. Bacteremia: Pathogens S. Aureus S. Pyogenes S. Pneumoniae H. Influenzae Enterobacteriaceae Bacteroides Pseudomonas Aeruginosa Candida species

4. Occurrence of False Positive Blood Cultures (Trash) True (%)Trash (%) S. aureus876 Coag negative staph1282 Enterococcus7016 Diphtheroids296 C. perfringens2377 C. albicans90

5. Blood Cultures: 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 Diagnostic yield increased by 3% for every 1 ml of blood drawn

6. Blood Cultures: 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

7. 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

8. Aim of the test Diagnosis of bacteremia by Aerobic and anaerobic cultivation of the blood, With identification and 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).

9. Aerobic/Anaerobic Blood Culture Bottles

10. 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.

11. Pathogens

12. 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.

13. 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.

14. 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. 1 st sample: 90% detection.

15. Quantity of specimen

16. 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.

18. 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.

19. 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.