美国范德堡大学医学中心临床微生物实验室主任 缺照片. Dr. Charles W. Stratton, IV

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1 Dr Stratton is currently Associate Professor of Pathology and Medicine and Director of the Clinical Microbiology Laboratory at the Vanderbilt University Medical Center in Nashville, Tennessee. Dr Stratton has board certifications in internal medicine, infectious diseases, medical microbiology and public health, and medical microbiology. He has held academic and hospital appointments in medicine, pathology, and clinical microbiology initially at West Virginia University College of Medicine and more recently at Vanderbilt University School of Medicine. Dr Stratton is a Fellow in the American College of Physicians, College of American Pathologist, American Society of Clinical Pathologists, American Academy of Microbiology, and Infectious Diseases Society of America. He served as editor of Topics in Clinical Microbiology. Dr Stratton also served as associate editor and then editor for Infectious Diseases Newsletter. 缺照片 Dr. Charles W. Stratton, IV 美国范德堡大学医学中心临床微生物实验室主任

2 Application of Blood Cultures for the Diagnosis of Infectious Diseases Charles W. Stratton, M.D. Vanderbilt University School of Medicine Nashville, Tennessee

3 Blood Culture Update Historical perspective Clinical and prognostic importance of positive blood cultures Scientific basis and fundamental principles of blood cultures Technical and clinical variables New data from recent studies

4 First Description of Blood Cultures Crookshank EM. A Textbook of Bacteriology To make a cultivation from the blood of a living person, the tip of a finger must be well washed with soap and water and sponged with 1 in 20 carbolic. Venous congestion is produced by applying an elastic band or ligature to the finger, which is pricked by a sterilized sewing needle. From the drop of blood which exudes the necessary inoculations and examinations can be made. Another way of extracting blood from the living person is to apply a leech. Blood may also be taken directly from a vein by laying it bare by dissection, making a small opening with a sterilised scissors, inserting a looped platinum needle, the needle of a hypodermic syringe, or a capillary tube.

5 Blood Culture Method

6 Requisites for Successful Blood Cultures in 1930 Pulvertaft,, RJV. Lancet 1:821-2 >10 ml of blood Blood to broth ratio > 1:5 3 blood cultures (SBE) Hold 14 days

7 First Successful Automated Blood Culture Instrument BACTEC 460 (early 1970s)

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9 First Continuous Monitoring Blood Culture Instrument BacT/Alert (1991)

10 Evolution of Blood Cultures Systematic studies have defined critical technical and clinical variables for improved detection of bacteremia and fungemia Volume of blood cultured Type of broth culture medium Ratio of blood to broth Atmosphere of incubation Agitation Additives: antibiotic-binding substances, agents that lyse phagocytic leukocytes

11 Clinical Importance of Bloodstream Infections Of all the microbiologic procedures performed in the laboratory, few are as important as the prompt recovery of microorganisms from blood. Washington J. Mayo Clin Proc Incidence of bacteremia Est. > 200,000 episodes annually in US Mortality 20-25% Nosocomial episodes > 50% in some hospitals Prolonged hospitalizations Increased mortality compared with community-acquired episodes

12 Diagnostic & Prognostic Importance of Positive Blood Cultures Diagnostic Establishes infectious etiology for patient s illness Provides organism for susceptibility testing and optimization of antimicrobial therapy Prognostic Index of failure of host defenses to contain infection at primary focus Index of failure of physician to remove, drain, or otherwise adequately treat primary infection

13 Technical Variables That Affect Blood Cultures Volume of blood cultured one of the most important variables Adults ml optimal Infants and small children 1-5 ml

14 Technical Variables That Affect Blood Cultures Culture medium Different broths not necessarily equivalent Same basal medium from different manufacturers may not perform in an equivalent manner Proprietary additives Performance affected by bottle conformation and headspace

15 Comparison of Yield by Medium Microorganisms Both media COL Only THIO Only P Staphylococci NS Streptococci <0.001 (S. pneumoniae) (29) (2) (23) (<0.001) Enterobacteriaceae <0.05 P. aeruginosa NS Anaerobes NS Fungi <0.001 (C. albicans) (10) (19) (1) (<0.001) ALL ORGANISMS NS

16 Comparison of Yield in Tryptic Soy Broth (Weinstein MP et al, J Clin Microbiol,, 21: , 629, 1985) Both SeptiChek Vacutainer Microorganisms Systems Only Only P Staphylococci <0.001 Streptococci <0.001 Enterobacteriaceae <0.001 P. aeruginosa <0.02 Anaerobes <0.01 Fungi NS ALL ORGANISMS <0.001

17 Technical Variables That Affect Blood Cultures Blood to broth ratio Dilution of blood at least 5-fold (1:5) Decreases inhibitory substances Phagocytic leukocytes Complement Lysozyme Immunoglobulins Decreases concentration of antibiotics if present in blood Lower ratios acceptable for some medium formulations

18 Technical Variables That Affect Blood Cultures Atmosphere of incubation Traditional 2 bottle set - aerobic and anaerobic 1970s up to 25% of episodes contained anaerobes Anaerobic bacteremia now less common Mayo Clinic (1990) - 45% decrease over 15 year period Barnes Hospital (1992) - 3 to 4-fold decrease from Proposed reasons for decrease in anaerobic bacteremia Earlier recognition and treatment of anaerobic infections Improved surgical prophylaxis Empiric use of antimicrobials with good anaerobic activity

19 Technical Variables That Affect Blood Cultures - Use of Anaerobic Bottles Suggestion that routine use of the anaerobic bottle be abandoned Murray et al (1992) - results of anaerobic blood cultures rarely influenced medical management Morris et al (1993) 84% of patients with anaerobic bacteremia detected only in the anaerobic bottle had signs or symptoms to suggest a site where anaerobes would be expected Therefore, use of 2 aerobic bottles routinely, with addition of an anaerobic bottle selectively, would detect 84% of anaerobic bacteremias

20 Comparison of Yield from 2 BacT/Alert FAN O 2 Bottles vs. Paired FAN O 2 & AnO 2 Bottles (Riley et al, J Clin Microbiol,, 41:213-7, 2003) Both Aerobic Combo Microorganisms Pairs Only Only P Staphylococci Streptococci NS Enterococci NS Enterobacteriaceae <0.05 Non-enteric GNR NS Anaerobes Fungi NS ALL ORGANISMS

21 Technical Variables That Affect Blood Cultures - Use of Anaerobic Bottles Considerations in deciding whether to use anaerobic bottles routinely or selectively Frequency of anaerobic bacteremia in one s hospital Medical staff awareness Logistical issues Different culture sets on different nursing units depending on patient population (e.g., abdominal surgery patients) Who draws the blood cultures? Phlebotomists (some control from lab) Non-phlebotomist HCWs (little/no control from lab) Residents and medical students (little/no control)

22 Technical Variables That Affect Blood Cultures Anticoagulant Most systems use SPS Interferes with phagocytosis Inhibits complement and lysozyme Inactivates aminoglycosides Inhibits N. gonorrhoeae, P. anaerobius Agitation Improves yield & speed of detection of positive cultures

23 Technical Variables That Affect Blood Cultures Inactivation or binding of antimicrobials BACTEC resin media Antibiotic binding resins on tiny glass beads BacT/Alert FAN and FN media Activated charcoal Both resin and FN media have enhanced yield in comparison with standard media Also detect more contaminants, especially CoNS, and cost more

24 Comparison of Yield in Resin and Non-Resin Media (Weinstein MP et al, J Clin Microbiol,, 29: , 882, 1991) Both Plus 26 SeptiChek Microorganisms Systems Only Only P Staphylococci <0.001 Streptococci NS Enterococci <0.005 Enterobacteriaceae <0.005 P. aeruginosa NS Anaerobes NS Fungi NS ALL ORGANISMS <0.001

25 Microorganisms and Septic Episodes Detected by BacT/Alert FAN vs. Standard Bottles (McDonald LC et al, J Clin Microbiol, 34: , 1996) Standard FAN Microorganisms Only Only P S. aureus 4 42 < Coagulase-negative staph 2 20 < Enterobacteriaceae 5 22 <0.005 Non-fermenting GNRs 6 2 NS Anaerobic bacteria 5 5 NS Fungi 7 7 NS Polymicrobial episodes 8 16 NS ALL EPISODES <0.0001

26 Contaminants Recovered from BacT/Alert FAN vs. Standard Bottles (McDonald LC et al, J Clin Microbiol, 34: , 1996) Standard FAN Microorganisms Only Only P Coagulase-negative staph < Other contaminants a NS All contaminants < a Propionibacterium spp., Corynebacterium spp., Bacillus spp. accounted for the majority of other contaminants

27 Technical Variables That Affect Blood Cultures Duration of incubation has decreased 7-14 days in 1970s 7 days during 1980s and early 90s Studies of continuous monitoring systems have shown that 5 days is sufficient in routine circumstances Consider extended incubation in special situations Brucella, Legionella, filamentous fungi (?), endocarditis (?)

28 Cumulative Recovery of Microorganisms from BacT/Alert Standard a and ESP Blood Culture Bottles b No. (% of total detected) Day of Incubation BTA O 2 Bottle BTA AnO 2 Bottle ESP System (75.8) 258 (73.9) 4757 (63.2) 2 53 (89.9) 52 (88.8) 1910 (88.6) 3 16 (94.1) 15 (93.1) 490 (95.1) 4 10 (96.8) 10 (96.0) 204 (97.8) 5 3 (97.6) 6 (97.7) 169 (100) 6 1 (97.9) 2 (98.3) No data 7 8 (100) 6 (100) No data a Wilson ML et al, Diag Microbiol Infect Dis, 16:31-34, 1993 b Doern GV et al, J Clin Microbiol, 35: , 1997

29 4-Day vs. 5-Day Yield of Positive Blood Cultures in BACTEC 9240 Aerobic Resin Bottles 1133 clinically significant isolates detected after 5 days of incubation 907 (80.0%) detected in < 24 hours 162 (14.3%) detected after hours All but 18 isolates detected after 96 hours (98.4%) Microorganisms detected on day 5 S. aureus 4 E. faecalis 1 Klebsiella spp. 5 Serratia sp. 1 Brucella sp. 2 Candida spp. 3 C. neoformans 1

30 Clinical Variables That Affect Blood Cultures Effectiveness of skin antisepsis Traditional goal: contamination rate < 3% CAP benchmark study of 640 institutions Schiffman et al, Arch Lab Clin Med, 1998 Median contamination rate 2.5% 90 th percentile 0.9% 10 th percentile 5.4% Antiseptic agents not immediately effective Iodophors (e.g., Betadine) minutes Iodine tincture 0.5 minute Other agents alcohol, chlorhexidine

31 Clinical Variables That Affect Blood Cultures Method of obtaining blood Venipuncture using needle and syringe remains the preferred method Direct draw Vacutainer-type, needle transfer devices Aspiration from IV catheters Increasing use Increased contamination rates If done, also obtain peripheral BC to validate

32 Clinical Variables That Affect Blood Cultures Number of BCs Virtually all adult bacteremias can be detected with 2 or 3 blood cultures if the volume of blood per culture is > 20 ml

33 Clinical Variables That Affect Blood Cultures Timing of blood cultures Depends more on the clinical status of the patient than on any other factor Li et al (1994) found that the interval between blood cultures was not important clinically Of blood cultures obtained within a 24 hour period, there were no differences in yield whether blood cultures were obtained simultaneously or serially over time

34 Interpretation of Positive Blood Cultures Clinical factors (some available only to physician) Pt. history, physical findings, WBC count, results of imaging studies, course of illness, results of cultures from other sites Laboratory factors suggested as being useful Microorganism identification Proportion of blood cultures positive (# positive vs. # obtained) Number of bottles positive in the blood culture set or sets Speed with which microorganisms are detected Typing of strains (esp. for CoNS) Molecular methods (e.g., PFGE) Traditional methods (biochemical profile, antibiogram)

35 Most Common Microorganisms Isolated from Blood Cultures (Weinstein MP et al. Clin Infect Dis,, 24: , 1997) Microorganism No. % True S. aureus E. coli Coagulase-neg staph K. pneumoniae Enterococci P. aeruginosa S. pneumoniae C. albicans Viridans group strep E. cloacae

36 Diagnostic Importance of Separate Blood Cultures (Weinstein MP et al, Rev Infect Dis 5:35-53, 53, 1983)

37 Other Potential Aids in Interpretation of Positive Blood Cultures Time to positivity Premise: pathogens are present in higher inocula than contaminating organisms and will be detected more quickly Number of bottles positive in a BC set Premise: pathogens are more likely than contaminants to grow in multiple bottles of a set Degree of overlap of trues and contaminants makes both methods unreliable Differential time to positivity may have value for dx of catheter-associated bacteremia (Raad et al, Ann Intern Med, 140:18-25, 2004)

38 Blood Culture Update Recent Studies Fewer than in the past Comparative clinical evaluations of continuous-monitoring systems have become more difficult to do IRB issues Sponsors budget limitations Marketing divisions dominate R&D

39 Comparison of Yield in BACTEC 9240 vs. BacT/Alert Standard Aerobic Media (Mirrett et al, J Clin Microbiol,, 41:2391-4, 4, 2003) Both BTA BACTEC Microorganisms Systems Only Only P S. aureus NS Coag-neg staph <0.05 Streptococci NS Enterococci NS Enterobacteriaceae NS Non-enteric GNR NS Anaerobes NS Fungi <0.01 ALL ORGANISMS <0.005

40 Comparison of Yield in BACTEC Resin/Lytic vs. BacT/Alert FAN Media (Mirrett et al. 102 nd Gen Mtg ASM, 2002) Both BacT/Alert BACTEC Microorganisms Systems Only Only P Staphylococci NS Streptococci NS Enterococci NS Enterobacteriaceae NS (E not Ec or Kp) (47) (8) (19) (<0.05) P. aeruginosa NS Other GNR NS Anaerobes NS Fungi <0.05 (C. albicans) (17) (10) (2) (<0.05) ALL ORGANISMS NS

41 Studies of BACTEC MYCO/F LYTIC Blood Culture Medium Designed for detection of fungi and mycobacteria in BACTEC 9000 system Contains supplemented Middlebrook 7H9 and brain heart infusion broth, specific proteins and sugars, saponin, and added oxygen and carbon dioxide Also capable of growing bacteria

42 Studies of BACTEC MYCO/F LYTIC Blood Culture Medium In HIV pts, MFL detected more C. neoformans but fewer H. capsulatum than ISO (Waites & Woods, JCM, 1998) In selected pts, MFL detected more yeasts than ISO and PLUS Aerobic and almost as many (18/19) H. capsulatum as Isolator (Fuller et al, JCM, 2001) In pts with suspected mycobacteremia, MFL was compared with 13A, ISO, & BTA MB (Crump et al, JCM, 2003) No significant differences between yields (n=94) Significant differences in time to detection MB<MFL<13A<ISO