Blood culture liaison process – advice by organism type- Gram positives

SECOND CLINICIAN CALL: Confirmed culture identification with susceptibility available

  • Prior to calling, check the isolate antibiogram to see that species and susceptibility are consistent – see EUCAST Expert rules which provide intrinsic resistance characters by species, including unusual phenotypes.
  • If possible speak to the same clinician who you initially contacted about the Gram stain result (look at your diary record !). Make sure your interaction has an proper formality about it – this is essential for building clinician respect for the laboratory service. See previous posting concerning ISBAR process.
  • Document additional clinical data required for completion of an Bloodstream infection event record after your contact (refer to this example template for these records with definitions of key data items). These records of significant BSI events are gold when it comes to analysis of local epidemiology of sepsis (community or hospital acquired/associated).

Specific advice by organism:

Staphylococcus aureus (Methicillin-susceptible = ‘MSSA’ and methicillin-resistant = ‘MRSA’)

  • Identification – confirmation of the S. aureus identification should usually occur by at least two independent methods – e.g. tube coagulase positive is the most reliable, mannitol fermentation, other phenotypic characteristics.
  • The screening test that confirms MRSA is done by a cefoxitin 30 microgram disc test by the correct EUCAST or CLSI methodology.  This posting discusses susceptibility of S. aureus.
  • Note well:  S. aureus bacteraemia is seldom due to contamination. One can only assume this if a) the patient has not received treatment and remains well AND b) a second blood culture is negative collected when not on Treatment.
  • Main presentations – Work through with the clinician on the phone the potential likely sources for the bacteraemia. Source control is an essential part of management.
  • Core antibiotics include flucloxacillin IV at high dose for MSSA and vancomycin IV for MRSA (if not available consult further for advice).  Empirical treatment in those facilities where the percent of BSI due to MRSA is above 15% or so, should include treatment that is active against MRSA (eg. IV vancomycin + flucloxacillin).
  • Detailed advice for clinicians is laid out in this posting – please read and understand it ; also suggest the clinician accesses it directly! 

(Also work with your local clinicians to establish standard treatment guidelines for S. aureus BSI that encompass these measures. Otherwise mortality is high and relapse likely!)

Streptococcus pneumoniae

  • Identification – consistent Gram stain, colony morphology and optochin susceptibility is usually sufficient.  Oxacillin disc screen is used to determine elevation of penicillin MIC.
  • Main presentations include pneumonia (all ages), meningitis (all ages), primary bacteraemia (infants) and sometimes joint infection. Toxic shock syndrome and necrotizing fasciitis possible.
  • Core antibiotics for treatment include ceftriaxone at high dose (reserve for meningitis) and benzylpenicillin followed by oral amoxycillin (non-CNS infection). Note that ceftriaxone is NOT recommended for pneumonia even when the penicillin MIC is elevated (MIC < 4 mg/L). This posting provides detailed clinical and lab advice.

Streptococcus pyogenes (Group A strep) and Groups B, C or G beta-haemolytic streptococci

  • Identification – consistent Gram stain, colony morphology and susceptibility is usually sufficient.  Latex Lancefield grouping is often done. See this posting for further advice on susceptibility.
  • Main presentations include cellulitis, other skin and soft tissue infection, joint infection, rarely pneumonia (all ages). Toxic shock syndrome and necrotizing fasciitis possible. Rheumatic fever of course!
  • Core antibiotics – see this posting as above –  IV – benzylpenicillin still best; oral – amoxycillin /ampicillin usual. Phenoxymethyl penicillin reserved for pharyngitis without bacteraemia.

Gram negatives – see next posting!

About mdjkf

Microbiologist and Infectious Diseases Physician
This entry was posted in Module - Blood cultures, Pathology, Quality management and tagged . Bookmark the permalink.

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