Blood culture 壢新醫院 病理檢驗科 陳啟清技術主任
A Positive Blood Culture Clinically Important Organism Failure of host defenses to contain an infection at its primary focus Failure of the physician to effectively eradicate, drain, excise, or otherwise remove that focus of infection Indicator of disseminated infection associated with poor prognosis
Clinical manifestation Bacteremia or Fungemia That simply identify the presence of bacteria or fungi respectively in the blood Sepsis The presence of clinical symptoms of infection in the presence of positive blood culture Septicemia Serious clinical syndrome associated with evidence of acute infection and organ failure related to release of mediators like cytokines into the circulation Septicemia may or may not be associated with positive blood culture 3
Clinical Patterns of Bacteremia and Fungemia Transient bacteremia lasting minutes to hours, is most common occur after the manipulation of infected tissue surgical procedure involve contaminated or colonized mucosal surfaces onset of acute bacterial infection 4
Clinical Patterns of Bacteremia and Fungemia Intermittent bacteremia occur, clear then recurs in the same patient due to the same microorganism Associated with under drained closed space infections Continuous bacteremia infective endocarditis occur early in the course of brucelosis and typhoid fever 5
Risk Factors for Bacteremia and Fungemia There is increased risk at the extremes of age; premature infants are especially at risk for bacteremia Some of illnesses: hemotologic/nonhematologic malignancies Diabetes mellitus renal failure requiring dialysis hepatic cirrhosis immune deficiency syndromes 6
Mortality rates and Risk Factors Associated with Bacteremia Condition Mortality(%) Related risk of death Age of patient < 20 13.8 1.0 21-40 32.8 2.33 41-50 42.9 3.06 >50 49.8 3.55 Source of infection IV catheter 1.1 1.00 Genitourinary 14.9 1.35 Foley catheter 37.8 3.38 Surgical wound 42.9 3.88 Abscess 51.2 4.65 Respiratory infection 52.3 4.73 7
Mortality rates and Risk Factors Associated with Bacteremia Condition Mortality(%) Related risk of death Predisposing Condition Surgery 16.3 0.78 Trauma 27.3 1.37 Diabetes mellitus 30.0 1.43 corticosteroids 33.3 1.59 Renal failure 37.5 1.79 Neoplasm 42.1 2.01 cirrhosis 71.5 3.40 8
Mortality rates and Risk Factors Associated with Bacteremia condition Mortality(%) Related risk of death Type of Organism Nonfermenters 27.7 6.84 Enterobactericaea E.coli 35.5 3.36 Kle.pneumoniae 48.0 4.52 Gram-positive cocci 32.7 3.08 Strept. neumoniae 22.0 2.08 Enterococci 45.5 4.28 Unimicrobial bacteremia 37.7 Polymicrobial bacteremia 63.0 5.96 Fungi 67.7 9
The 10 major pathogens causing bacteremia and fungemia in adults from 1975 to 1977 and 1992 to 1993 Microorganism 1975-1977 E. coli S. aureus S. pneumoniae K. pneumoniae P. aeruginosa B. fragilis Enterococcus spp. S. pyogenes C. albicans P. mirabilis 1992-1993 S. aureus E. coli CNS K. pneumoniae Enterococcus spp. P. aeruginosa S. pneumoniae Viridans groups streptococci C. albicans E. cloacae
Major Pathogens Causing Nosocomial Bloodstream Infections, 1981-1998 % of isolates Pathogen Rank 1981-6 1987-92 1993-8 (899) (1655) (5209) Candida spp. 1.0 9.2 16.4 1 S. aureus 5.2 9.3 11.5 2 E. coli 18.7 9.7 8.7 3 CoNS 2.7 8.5 7.9 4 K. pneumoniae 11.6 6.6 7.7 5 Enterobacter spp. 8.0 8.6 7.3 6 Acinetobacter spp. 6.1 8.8 7.2 7 P. aeruginosa 10.0 9.4 7.2 8 Other NFGNB 5.9 7.7 6.8 9 Enterococcus 8.7 6.2 6.3 10
Blood Culture Collection Guidelines Number of Cultures Adult patients Two or three blood cultures per septic episode >95% detection ensuring adequate volumes of blood distinguish between clinically important and contaminant More than three blood cultures do not help distinguish between clinically important and contaminant expensive
Larry et al. 1997. Clin. Microbiol.Rev.
Blood Culture Collection Guidelines Set (Aerobic/Anaerobic, Two-Bottles) Number Acute sepsis 2-3 sets, separate sites, within 10 min Endocarditis, acute 3 sets, separate sites, over 1-2 h Endocarditis, subacute 3 sets, separate sites, 15min apart; if negative at 24h,3 more sets FUO 2-3 sets, separate sites, 1h apart; if negative at 24h, 3 more sets Manual of Clinical Microbiology 2000
Blood Culture Collection Guidelines Disinfection Culture Bottle 70% isopropyl alcohol to rubber stoppers and wait 1 min Venipuncture site 70% alcohol Swab concentrically with iodine preparation Allow iodine to dry Do not palpate vein Collect blood Remove iodine with alcohol
Blood Culture Collection Guidelines Blood Volume Higher volume most productive Aerobic/anaerobic two-bottle set Adult: 10-20 ml/set Infant: 1-10 ml/set
Blood Culture Collection Guidelines Timing of Cultures Soon after fever spike No difference in drawn simultaneously and serially over a 24-h period Li et al. 1994. J. Clin. Microbiol.
Blood Culture Collection Guidelines Collection Procedure Not drawn from indwelling vascular catheters Culture bottle disinfected with alcohol swab Collected by venipuncture of peripheral veins Iodine should not be used to disinfect bottle Iodine or iodophore should be used in patients and wait for 1-3 min
Regarding skin preparation with iodine for venipuncture; bacteria are killed by drying, not by drowning. Frank Koontz, Ph.D. University of Iowa Hospitals Iowa City, Iowa
A schematic overview of the Microbiology Laboratory Examine Stain Culture ID/AST Specimen Report Preliminary report Phone report
Blood Culture Methods Manual Conventional broth Biphasic Lysis-centrifugation Automated BACTEC 460, 660,730, 860 BacT/Alert BACTEC 9000 series Difco ESP biomerieux Vital Bio Argos
Principles of Laboratory Detection Volume of blood Culture Adult patient The most important variable <1-10 CFU/ml Increasing 1 ml, increasing microbial recovery up to 3% Children or infant 100-1000 CFU/ml Increasing volume, increasing yield Mermel & Maki 1993. Ann. Innter. Med.
Principles of Laboratory Detection Ratio of Blood to Broth Blood: broth (1:5 1:10) Diluting antimicrobial agents Diluting natural inhibitory factors Prevent clotting
Huang et al. 1998. Eur.J..Clin..Microbiol. Infect. Dis.
Pitfalls about Blood Cultures Prolonged incubation (2-4 weeks) Brucella, Bartonella Subacute bacterial endocarditis, FUO Faint gram-negative bacteria Campylobacter, Helicobacter, Legionella, Brucella, Bartonella
Catheter-Drawn Blood Continues to increase Patients: little discomfort Physicians Ease of drawing blood Keeping catheter in place and treating with antibiotics without removal of the catheter Identifying catheter-related septicemia: higher CFU from catheter-drawn vs. peripheral blood Laboratory: NOT recommended
Management of Bacteremia Essential Aspects Early clinical recognition of sepsis Rapid laboratory detection of the causative organisms Prompt initiation of appropriate antimicrobial therapy
Notification and Reporting of Positive Blood Cultures Gram-stained Morphotype Preliminary Results Bacterial Genus and Direct AST Definitive Results Bacterial Species and Indirect AST
Positive Blood Culture Bottles Gram-Stained Morphotypes Gram positive versus Gram negative Bacilli, cocci, coccobacilli, curved bacilli, and others Differentiation among Staphylococci, pneumococci, enterococci, other streptococci Enterobacteriaceae, NFGNB, Acinetobacter spp. Others (Campylobacter, Helicobacter spp. etc.) C. glabrata, other Candida spp, and Molds Communications between clinicians and microbiologists
Positive Blood Cultures Preliminary Results Presumptive bacterial ID Direct AST results General panel Specific panel Definitive Results Definitive bacterial ID Indirect AST results Specific panel Difference between general and specific panels