From the Guidelines
Blood cultures are not routinely recommended in the management of cellulitis, except in specific cases such as severe infection, immunocompromised patients, or when there's concern for bacteremia. The Infectious Diseases Society of America guidelines from 2014 suggest that cultures of blood or cutaneous aspirates, biopsies, or swabs are not routinely recommended for typical cases of cellulitis 1. This is because the yield of blood cultures is low, with positive results in only a small percentage of patients, and these rarely alter management decisions.
The guidelines do recommend considering blood cultures in patients with specific risk factors, such as malignancy on chemotherapy, neutropenia, severe cell-mediated immunodeficiency, immersion injuries, and animal bites 1. In these cases, blood cultures may help guide antibiotic therapy and identify the causative organism.
When it comes to antimicrobial therapy, the guidelines recommend an antimicrobial agent that is active against streptococci for typical cases of cellulitis without systemic signs of infection 1. For more severe cases, broader antibiotic coverage may be necessary, including coverage against methicillin-susceptible S. aureus (MSSA) or methicillin-resistant S. aureus (MRSA) 1.
Key points to consider when deciding whether to obtain blood cultures in cellulitis cases include:
- The severity of the infection
- The presence of systemic signs of infection
- The patient's immune status
- The presence of specific risk factors, such as animal bites or immersion injuries
- The potential for bacteremia or sepsis.
Overall, the decision to obtain blood cultures in cellulitis cases should be individualized based on the clinical presentation and risk factors, rather than performed routinely for all cases 1.
From the Research
Role of Blood Cultures in Cellulitis Management
- Blood cultures are not routinely recommended for uncomplicated cellulitis, as they rarely change management from empirical coverage 2, 3, 4.
- In complicated cellulitis, blood cultures may be useful, but they still have a low yield and rarely result in a change in antibiotic therapy 2.
- However, in elderly patients, blood cultures may be more useful, with a higher proportion of bacteremia and a lower skin contamination rate 5.
- The decision to obtain blood cultures should be based on clinical judgment, taking into account factors such as the presence of comorbidities, severity of infection, and risk of bacteremia 5, 4.
Factors Associated with Bacteremia in Cellulitis
- Age, with older patients having a higher risk of bacteremia 5.
- Presence of comorbidities, such as diabetes, immunosuppression, or organ transplantation 2.
- Severity of infection, with more severe cases having a higher risk of bacteremia 5.
- Clinical presentation, with symptoms such as shaking chills and leukocytosis increasing the risk of bacteremia 5.
Microbiology of Cellulitis
- The most common pathogens involved in cellulitis are Streptococcus and Staphylococcus species 5, 3, 6.
- Gram-positive cocci are the most common cause of bacteremia in cellulitis, with Streptococcus dysgalactiae being a common pathogen 5.
- Methicillin-resistant Staphylococcus aureus (MRSA) is not typically covered in uncomplicated cellulitis, unless there are risk factors for MRSA infection 6.