# AI misinterprets a single positive blood culture for coagulase-negative staphylococci as true bacteremia, leading to unnecessary vancomycin therapy

- **ID:** `medical/blood-culture-contamination-misinterpretation`
- **Domain:** medical
- **Category:** data_error
- **Error Code:** `BC-CONS-FALSE-POS`
- **Verification:** ai_generated
- **Fix Rate:** 88%

## Root Cause

Coagulase-negative staphylococci (CoNS) are common skin contaminants; true bacteremia requires at least two positive cultures from separate venipunctures or one positive from a sterile site. A single positive bottle has a 70-80% probability of contamination, but AI treats it as definitive infection.

## Version Compatibility

| Version | Status | Introduced | Deprecated |
|---------|--------|------------|------------|
| BD BACTEC FX v5.0 | active | — | — |
| bioMerieux VITEK MS v3.2 | active | — | — |
| Thermo Fisher VersaTREK v2.1 | active | — | — |

## Workarounds

1. **Implement a rule-based alert: if only one of two sets is positive for CoNS, flag as 'probable contaminant' and recommend repeat culture from two separate sites before starting antibiotics** (88% success)
   ```
   Implement a rule-based alert: if only one of two sets is positive for CoNS, flag as 'probable contaminant' and recommend repeat culture from two separate sites before starting antibiotics
   ```
2. **Use time-to-positivity (TTP) analysis: CoNS contaminants typically grow >24 hours; true bacteremia grows <16 hours; if TTP >24h, defer antibiotics and repeat** (85% success)
   ```
   Use time-to-positivity (TTP) analysis: CoNS contaminants typically grow >24 hours; true bacteremia grows <16 hours; if TTP >24h, defer antibiotics and repeat
   ```
3. **Integrate with electronic health record (EHR) to check for clinical signs of sepsis (fever, WBC, CRP) before acting on single positive CoNS; if no signs, observe and repeat** (90% success)
   ```
   Integrate with electronic health record (EHR) to check for clinical signs of sepsis (fever, WBC, CRP) before acting on single positive CoNS; if no signs, observe and repeat
   ```

## Dead Ends

- **** — Vancomycin is nephrotoxic and promotes resistance; if contamination, patient receives unnecessary antibiotics with risk of AKI (70% fail)
- **** — Repeating from the same IV line may yield same contaminant; need separate venipuncture from another site to rule out contamination (60% fail)
- **** — Guidelines require two positive sets for CoNS; AI may not check number of sets drawn or time to positivity (55% fail)