#EMConf: Should We Order Blood Cultures in the Emergency Department for Patients Admitted with Cellulitis?

 The Bottom Line: Emergency medicine providers over-order blood cultures in patients admitted to the hospital with cellulitis. Blood culture results do not alter the course of treatment, even when positive. The IDSA guidelines give adequate recommendations of when to draw blood cultures. Blood cultures should be drawn for patients admitted with cellulitis AND at least one of the following:
1.     Malignancy ON chemotherapy
2.     Severe systemic features such T>38C (100.4F), hypotension (BP threshold not defined) HR >90, or RR>24
3.     Neutropenia
4.     Severe cell-mediated immunodeficiency
5.     Immersion injury
6.     Animal bites
Study 1: Bauer, Sophie, et al. “Blood Cultures in the Evaluation of Uncomplicated Cellulitis.” European Journal of Internal Medicine. 12 Aug. 2016.
·Retrospective cohort study of 467 patients presenting to the ED with uncomplicated cellulitis who were admitted to one of six hospitals in both urban and rural Switzerland between January 2011 and December 2014.
·250 (52.5%) of the 467 patients had blood cultures drawn. Of these, 12 (4.8%) had true bacteremia, and 4 (1.6%) had positive blood cultures, which were contaminants.
·After excluding cases where blood cultures were recommended by the current IDSA guidelines (above), 185 (48.4%) of the 382 remaining individuals had blood cultures unnecessarily drawn, bacteremia was present in 4 of these patients (2.2%) and all four had Strep species.
·This study was retrospective and Switzerland has a different patient population than the USA.
·Infectious organisms likely have different rates of prevalence compared to the USA. Rates of MRSA are likely higher here. None of their positive blood cultures grew MRSA.
·25.6% of the patients received antibiotics before blood specimens for cultures were obtained, so rates of positive blood cultures may have been deceivingly low.
Study 2: Torres, Jesus, et al. “Low Yield of Blood and Wound Cultures in Patients with Skin and Soft-Tissue Infections.” The American Journal of Emergency Medicine. 26 May 2017.
·Prospective cohort study of 246 patients diagnosed with skin and soft tissue infections who were admitted between June 2010 and January 2013 to a single urban Level Trauma Center in the USA.
·Eighty-six patients (35%) out of the 246 enrolled had blood cultures drawn, of which six (7%) had positive results.
·This study compared patients with and without fever and found no significant difference in yields between febrile (yield 3.4%, 95% CI 0.6–17.2%) vs. afebrile (yield 8.9%; 95% CI 3.9– 19.3%) patients due to overlapping confidence intervals.
·This study also compare patients who were or were not IV drug uses and found no significant difference in yields between IV drug users (yield 8.7%; 95% CI 3.4–20.3%) vs. non IV drug users (yield 5.0% CI 1.4–16.5%) who had positive blood cultures, due to overlapping confidence intervals.
·All organisms found in positive blood culture results were susceptible to standard empiric skin and soft tissue antibiotics. Course of treatment unaffected by positive results.


·Excluded transferred patients and patients seen at a wound care clinic, which could have added patients with more severe cellulitis and more likely to have positive blood cultures.
·Did not record or control for antipyretics.
·75% of patients were male, which could be a confounding.
·Took place in California, certain bacteria may be more or less prevalent than other areas of the US. (All of their positive blood culture results grew MSSA and MRSA.)