You are treating a patient with left lower leg cellulitis. The nurse is going to establish IV access, draw blood work, and give analgesia and antibiotics. Before walking into the room, the nurse asks, “Do you need me to grab a set of blood cultures?” Additionally the hospitalist had asked you to order a “set of cultures” on your most recent cellulitis admission. Should you proceed?
Background
Cellulitis is one of the ten most common complaints in the ambulatory care setting which includes the emergency department. 1–3 Patients are subclassifed into either complex or simple cellulitis depending upon their comorbidity.
- Complicated cellulitis is defined as the presence of an immune-compromised status (HIV/AIDS, in active chemotherapy, status post organ transplantation), diabetes, or peripheral vascular insufficiency. Due to the extensive comorbidity, it typically requires treatment in the inpatient setting and blood cultures have been routinely recommended.
- Uncomplicated (simple) cellulitis is most often treated with oral antibiotics that cover for Staphylococcus and Streptococcus species based on local antibiograms.
Utility of Blood Cultures in Uncomplicated Cellulitis
In 2005, Mills et al 4 performed a search of the best available evidence on blood cultures in patients with cellulitis. Five articles were identified:
| Authors | Positive cultures | Contaminated cultures |
| Perl et al | 11/553 (2%) | 20/553 (3.6%) |
| Kulthanan et al | 20/150 (17.2%) | |
| Lutomski et al | 4/25 (16%) | 4/25 (16%) |
| Ho et al | 1/130 (0.77%) | 0/130 (0%) |
| Hook et al | 2/13 (4%) | No mention |
The authors conclude:
“On the basis of the evidence available, blood cultures do not significantly alter treatment or aid in diagnosing the microbial organism in acute adult cellulitis in normal immunocompetent hosts. Therefore, it would be within the standard of care not to obtain blood cultures in immunocompetent patients who present with apparently uncomplicated cellulitis.”
Utility of Blood Cultures in Complicated Cellulitis
In a retrospective chart review by Paolo et al 5 in 2013, patients were classified by the authors as having complicated or uncomplicated cellulitis. All of the study participants had blood cultures drawn and a comparison was made between the two groups to determine the utility of cultures in this setting. The results were:
| Cellulitis Type | Positive blood cultures | Contaminated blood cultures |
| Complicated | 29/314 (9%) | 13/314 (4%) |
| Uncomplicated | 17/325 (5%) | 10/325 (3%) |
The authors stated, “A clinically significant change in management (a change in the class of antibiotic) was found in 6 of 314 cases vs. 4 of 325 controls (p =0.578; OR=1.5525; 95% CI 0.434–5.5541)… This group of clinically significant change in management was about 2% of the entire cohort and most would have been changed to a narrowed antibiotic. “
| Patient # | Initial Antibiotic | Second Antibiotic | Blood Culture | Comorbidity |
| 1 | Keflex | Zosyn, Vancomycin | Cornebacterium | Diabetes |
| 2 | None | Augmentin | Stapylococcus saccharolyticus | Diabetes |
| 3 | Vancomycin | Penicillin G | Group B Strep | Diabetes |
| 4 | Zosyn, Flagyl | Cephalexin | Streptococcus salivarius | Chemotherapy |
| 5 | Clindamycin | Oxacillin | Group B Strep | Chemotherapy |
| 6 | Keflex | Linezolid | MRSA | Asplenia |
Additionally, out of their entire cohort, only 7 cultures were shown to have gram-negative bacteria. Due to the study time period (2005-2009), MRSA was not as prevalent in their community and is likely more common presently.
Conclusion
In both uncomplicated and complicated cellulitis, blood cultures have a low yield of becoming positive and when they are found to be non-contaminated, they are unlikely to significantly change management. The cases in which non-skin flora grow in the blood, the history from the patient usually has given the provider some cause to suspect bacteria other than routine skin flora.
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