Clinician Guide for Collecting Cultures

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

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.
  (Note: Determining if a BSI is a CR-BSI may be useful clinically. However, this definition of CR-BSI is not used for surveillance of CLABSI through NHSN. For the NHSN surveillance criteria, please refer tohttp://www.cdc.gov/nhsn/PDFs/pscManual/4PSC_CLABScurrent.pdf [PDF - 141.23 KB])
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.

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

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

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)

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

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

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

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