Skip directly to search Skip directly to A to Z list Skip directly to navigation Skip directly to site content Skip directly to page options
CDC Home

Clinician Guide

Ed Septimus, MD, FACP, FIDSA, FSHEA
Medical Director Infection Prevention and Epidemiology

Source: HCA Clinical Services Group, Nashville, TN

If possible cultures should be obtained before starting antimicrobial therapy; prior antimicrobial therapy may interfere with bacterial growth.

Blood cultures

  • Disinfect bottle tops with 70% isopropyl alcohol (alcohol pad);  clean puncture site with alcohol followed by chlorhexidine (CHG) and allow to dry
  • For adults, collect 10-20 cc and 1-3 cc for a child for each blood culture set; divide blood into two blood culture bottles, one for aerobes and one for anaerobes;  two or three blood cultures (by separate stick) per septic episode is sufficient.
    • Laboratory confirmed bloodstream infection (not central line related)
      • 1 positive blood culture with recognized pathogen from a  venipuncture
      • Skin organisms: >2 blood cultures drawn on separate occasions positive for the same organism plus clinical symptoms
  • For suspected catheter-related bloodstream infection (CR-BSI) draw one set through device and one set from a separate venipuncture.  Blood cultures from both line and venipuncture must be positive for same organism with clinical signs and symptoms and no other recognized source.  A positive culture from the line only is probably a contaminant and should not be treated.
    • Preferred Criteria for CR-BSI:
      • Differential  period of central line culture versus peripheral blood culture positivity > 2 hours
      • Simultaneous quantitative blood cultures with a ≥5:1 ratio central line versus peripheral blood culture
    • Alternative:
      • Draw one set through device and one set from a separate venipuncture for routine blood culture

Top of Page

Intravenous catheter tips

  • Remove aseptically and cut a ~4 cm segment from tip and place in sterile container; transport rapidly to prevent drying out;
    • Semiquantitative culture of catheter tips is usually performed by rolling the tip across an agar plate; the presence of >15 colonies along with the same organism isolated from peripheral blood with clinical signs and symptoms and no other recognized source  is consistent with a CR-BSI.
  • Comment: A positive catheter tip by itself is not diagnostic for a CR-BSI;   Do not routinely culture catheter tips on removal unless there are clinical signs and symptoms for infection.

Top of Page

Wound/abscess

  • Clean surface of wound or abscess with 70% alcohol and allow to dry;  aspirate pus or fluid if possible and either transport in syringe(preferred) or  place in anaerobic transport vial;  anaerobic transport tubes are appropriate for aerobic and anaerobic cultures;  always request a gram stain for initial guidance and comparison
  • Swabs should be discouraged since swabs usually have insufficient material for gram stain and culture;  if swabs must be used be sure quantity is adequate for both culture and gram stain
  • Do not culture chronic superficial wounds or sinus drainage since superficial cultures correlate poorly with deep cultures-try an obtain a deep culture or biopsy for culture whenever possible

Top of Page

Sputum

  • Have patient rinse with water to remove excess oral flora; instruct patient to cough deeply and collect and transport in a sterile container;  microbiology should perform a cytologic screening  specimens that are contaminated with oral secretions (presence of >10 squamous epithelial cell/LPF) and recommend re-collection if specimen is inadequate; gram stain should be performed on all sputum specimens

Top of Page

Tracheal aspirate

  • Does not need to be screened like sputum; perform gram stain along with routine cultures;  lab should report if specimen is purulent (>25 WBC/LPF)

Top of Page

Bronchial alveolar lavage (BAL) and mini-BAL

  • Obtained by bronchosopy or with use of a special catheter(mini-BAL); requires  prompt transport to the laboratory for processing;  not acceptable for anaerobic cultures; fluid should be concentrated for optimal yield for stains and cultures; consider quantitative bacterial cultures to guide interpretation with >104 CFU/mL considered significant

Top of Page

Urine

  • Midstream
    • Instruct women to hold labia apart, discard the first portion of voided urine and collect midstream urine in a sterile container
    • Instruct men to retract foreskin(uncircumcised), discard first portion of voided urine and collect in sterile container
  • Catheterized
    • Short-term collect specimen by aseptically aspirating from port of urinary catheter
    • Long-term change urinary catheter: first change urinary catheter then collect specimen by aseptically aspirating port of urinary catheter
    • Caution: straight cath for urine collection may result in iatrogenic UTI
  • Transport: keep urine refrigerated and send to microbiology lab promptly;  if significant delay is anticipated (e.g. regional lab) put urine in a tube with boric acid to prevent overgrowth  of contaminating organisms
  • Comment: Do not treat asymptomatic bacteriuria except in pregnancy or GU instrumentation

Top of Page

Stool

  • Collect specimen in a sterile container and transport promptly to microbiology lab; notify micro if a specific pathogen suspected (e.g. Vibrio, Yersinia, E. coli O157:H7, C. difficle)
  • Comments:
    • In general do not process for bacterial pathogens if patient develops symptoms more than 3 days after admission; consider C. difficile for hospitalized patients with diarrhea
    • Multiple specimens per day are not indicated
    • Formed stools in general should not be submitted

Top of Page

CSF

  • For bacteria send 1-2 mL for bacteria; if mycobacteria or fungi suspected send 5-10 mL
  • Comments
    • In general for initial evaluation, send CSF for cell count, glucose (also draw simultaneous blood glucose), and protein with gram stain and bacterial culture
    • Do not routinely order bacterial antigens, AFB, and fungi, or PCR for herpes until initial results from routine studies are available;  drawing  an extra tube to save for additional studies pending initial results is more appropriate and cost effective

Top of Page

 
Contact Us:
  • Centers for Disease Control and Prevention
    1600 Clifton Rd
    Atlanta, GA 30333
  • 800-CDC-INFO
    (800-232-4636)
    TTY: (888) 232-6348
  • Contact CDC–INFO
USA.gov: The U.S. Government's Official Web PortalDepartment of Health and Human Services
Centers for Disease Control and Prevention   1600 Clifton Road Atlanta, GA 30329-4027, USA
800-CDC-INFO (800-232-4636) TTY: (888) 232-6348 - Contact CDC–INFO
A-Z Index
  1. A
  2. B
  3. C
  4. D
  5. E
  6. F
  7. G
  8. H
  9. I
  10. J
  11. K
  12. L
  13. M
  14. N
  15. O
  16. P
  17. Q
  18. R
  19. S
  20. T
  21. U
  22. V
  23. W
  24. X
  25. Y
  26. Z
  27. #