Clues that a bacteremia represents a true infection:
- > 1 blood culture positive for the same organism
- 1 + BCx for Coagulase-negative staph is not usually a true infection
- Infection with the same organism at another site – e.g. pneumonia
- Time to positive culture < 3 days
Table 1: Chance that a single +blood culture for the following organisms represents contamination vs a true infection.
| Pathogen | % Contaminants |
|---|---|
| Staphylococcus aureus | < 1 |
| Enterobacterales eg E. coli | < 1 |
| Pseudomonas aeruginosa | < 1 |
| Streptococcus pneumoniae | < 1 |
| Group A streptococcus | < 1 |
| Candida spp. | < 1 |
| Listeria monocytogenes | < 1 |
| Alpha hemolytic strep (viridans) | 48 |
| Coagulase negative staph. * | 78 |
| Diptheroids (not JK) | 79 |
| Bacillus spp. (not anthracis) | 94 |
| Propionibacterium acnes | 99 |
* Clues to true infection: >1 + blood culture WITH same antibiogram, line-related, prosthetic valve, immunocompromised