Management of Positive Blood Cultures

Reporting Stages Reference

Stage 1 (1–2 hours): Gram stain and microscopy.
- Refer to flowcharts below for initial management.
- If Gram-stain appearance is ambiguous, refer to both the Staphylococci and Streptococci flowcharts and prioritise treatment for the most likely clinical source.

Stage 2 (8–24 hours): Preliminary ID and provisional susceptibilities (Rapid Antimicrobial Susceptibility Testing; RAST).
- Caution: Any decisions made based on provisional results must be reviewed against the final report.
Stage 3 (24–48 hours): Final report with definitive IV and oral options.
- Note: If no oral option is listed, no suitable agent was identified during testing.

Initial Management Flowcharts

The four management flowcharts are:

Stage 2 Review Checklist: Interpretive Guidance

When reviewing provisional identification and susceptibilities (RAST):

Confirm ID Relevance: Check if the identified organism matches the clinical picture (e.g., E. coli in a patient with suspected urosepsis).
Verify Treatment Efficacy: If the current antimicrobial is reported as "R" (Resistant), switch immediately to an agent reported as "S" (Susceptible) or "I" (Susceptible, increased exposure).
Check for "Red Flag" Phenotypes: Identify high-risk resistance such as MRSA, VRE, ESBL, or CPE.
Infection Control: Ensure appropriate isolation or contact precautions are in place for MRSA, VRE, Carbapenemase Producing Enterobacteriaceae (CPE), N.meningitidis, or Group A Streptococcus / S.pyogenes.
Deteriorating Patients: For any patient with a NEWS2 ≥7, seek urgent senior clinical review from your own specialty team.
Acknowledge Reporting Limitations: Be aware that provisional susceptibilities at Stage 2 must be confirmed with the final report.
Temocillin Exceptions: Note that enteric gram-negatives are never reported as "S" for temocillin, only as "I" or "R". Temocillin has no activity against P.aeruginosa or gram-positive organisms.
Plan for Stage 3: Document the changes made and ensure they are cross-referenced against the Stage 3 Final Report (24–48 hours) for confirmation.

See table 1 below for summary of actions based on microbiology report stage.

Table 1: Summary of actions based on microbiology report stage

Stage	Data Available	Mandatory Clinical Action
1	Gram stain only	Use initial management flowcharts above to start empirical therapy
2	ID + Provisional Rapid Antimicrobial Susceptibility Testing (RAST) results	Active review required. Switch if current treatment is ineffective = “R”
3	Final ID + Susceptibilities	Active review required. Confirm treatment; look for de-escalation or IV-to-oral switch (IVOS) options.

Documentation Requirement

All decisions derived from the management flowcharts or Stage 2/3 reports, especially when made in the absence of a consultant, must be documented in the patient's case notes.

Pathogen Guide

Please see table 2 for pathogen guide on significance and actions.

Table 2. Pathogen Significance and Action Guide.

Organism (gram stain)	Significant?	Clinical Actions and Considerations
S. aureus / MRSA	Always	Follow SAPG guidance; high risk of endocarditis or deep-seated infection
*S. lugdunensis*	Likely	Treat as S. aureus; can cause aggressive endocarditis
Other staphylococcal species, so-called “Coagulase-negative Staph”	Unlikely	Usually skin contaminants unless isolated repeatedly or prosthetic material present
S. pyogenes (“Group A Streptococcus”)	Always	Notifiable disease; requires contact precautions; universally penicillin-susceptible
*S. pneumoniae*	Always	Consider pneumococcal meningitis; HIV testing advised
Enterococcus spp.	Always	Possible endocarditis (especially E. faecalis); check for GI/UTI sources
“Viridans streps”, e.g. *S.mitis* *S.oralis* *S.mutans* *S.sanguinis*	Possible	Occasional contaminants, but also possible causes of sub-acute infective endocarditis. Reproducibility increases significance.
"Strep milleri" group *S.anginosus* *S.intermedius* *S. constellatus*	Always	High association with deep-seated abscesses; GI/oral source common. Anaerobic co-infection common.
"Strep bovis" group *S.gallolyticus* *S.infantarius* *S.pasteurianus*	Always	Associated with colorectal cancer; review for endocarditis; consider colonoscopy.
Gram-negative Bacilli, E.g. E.coli, Klebsiella spp., Proteus spp, Enterobacter spp., P.aeruginosa	Always	Common in urosepsis/abdominal sepsis. P. aeruginosa never susceptible to temocillin.
Yeasts	Always	Critical finding (60% mortality); start Caspofungin IV 70mg immediately.
Other skin organisms, e.g. *Micrococcus luteum* *Cutibacterium* spp. Propionibacterium spp.	Unlikely	Usually skin contaminants unless isolated repeatedly or prosthetic material present

Determining Clinical Significance

If the clinical significance of a result is in doubt, apply the following logic:

Organism Type: Skin commensals (organisms with “unlikely” significance in Table 2: Pathogen Significance and Action Guide) found in a single set in a patient without additional risk factors are likely contaminants.
Time to Positivity (TTP): Growth of an organism of uncertain significance detected after >48 hours is more likely to be a contaminant.
Reproducibility: A result is highly significant if the same organism is detected in multiple separate culture sets taken over a period of time.

Action: If significance is unclear, repeat blood cultures (ideally peripheral (first) + line if applicable) before making major treatment changes.

Guideline reviewed	March 2026
Page updated	July 2026