Topic Editor: Grant E. Fraser, M.D., FRACGP, FACRRM, ASTEM
Review Date: 10/7/2012
Definition
Cellulitis is an acute spreading non-necrotizing infection of the skin, which results in skin swelling, warmth, edema, erythema and discomfort. The affected tissue level is primarily the subcutaneous tissue and dermis.
Description
- Patients usually present with a region of skin that is painful, swollen, warm, tender and erythematous
- Fever may or may not be present
- Some patients will be systemically unwell with the rare presence of septic shock
- Cellulitis usually affects the epidermis and dermis; rare cases may extend into the fascia, including cases of necrotizing infection
- Most cases are caused by Staphylococcus aureus or Streptococcus pyogenes
- Clinical findings in cellulitis may be due to pyrogenic exotoxins produced by beta-hemolytic streptococci and local production of inflammatory cytokines by keratinocytes
Epidemiology
Incidence/prevalence
- The prevalence of cellulitis is unclear as it is not a reportable condition; however, one source indicates the incidence in the U.S. is 24.6 cases per 1,000 person-years
Age
- Cellulitis is more common in adults >45 years of age and in children 3 years of age
- Buccal cellulitis is more common in children 3 years
Gender
- Cellulitis is slightly more common in males with perianal cellulitis being more common in boys
Risk factors
- Chronic dermatosis such as psoriasis or eczema
- Elderly
- Lymphedema or venous insufficiency to the extremities
- Obesity
- Peripheral vascular disease, especially with open wounds
- Prior episode(s) of cellulitis
- Recent injury to the skin
- Recent surgical procedure
- Underlying conditions such as diabetes, renal failure, immunosuppression
Etiology
- Cellulitis is caused by the entry of microorganisms through the epidermis into the dermal subcutaneous tissues where the causative bacteria multiply. The result is localized infection, which later spreads along the dermal subcutaneous layer
- The most common bacteria responsible for cellulitis are Streptococcus pyogenes and Staphylococcus aureus
- Other causes often relate to underlying risk factors or unusual sources of a wound
- Other causes include:
- Gram negative bacteria, which only rarely cause cellulitis, including proteus, pseudomonas, enterobacteriaceae, citrobacter
- Anaerobic bacteria
- Mycobacteria
- Rarely, fungal causes, such as cryptococcus
- Marine wound source can lead to cellulitis caused by vibrio species
- Bites of cats and dogs can lead to Pasteurella multocida or septica, Capnocytophaga, Vibrio vulnificus, or Pasteurella cannus infection
- Human bites can result in Eikenella corrodens infection
History
- Patients typically present with a painful, inflamed, warm, red area of skin
- May or may not have fever
- May or may not be systemically unwell (dizziness, weakness, aches, nausea, headache)
- May have red streaking from the site of cellulitis consistent with lymphangitis and may have regional lymphadenopathy
- Risk factors may be present such as an acute wound, immunosuppression, diabetes, vascular insufficiency, lymphedema, or renal insufficiency
- Patients may present with other systemic symptoms such as fever, chills, malaise, collapse, hypotension, nausea, vomiting
Physical findings on examination
- An area of skin which has localized swelling, erythema, warmth, and some degree of subcutaneous edema
- Patients may have purulent drainage from open wounds
- Some patients will have abscess formation, which will typically be manifest as a fluctuant mass
- There may be lymphangitis and lymphadenopathy proximal to the cellulitis
Blood tests findings
- Although blood tests are commonly ordered, they are not particularly useful in most cases. A careful clinical review of the extent of infection and degree of systemic illness is sufficient in most cases.
- If a CBC is ordered; it will either be normal, or show a leukocytosis, generally with a left shift.
- If inflammatory markers are ordered, it is typical to have elevation in the Erythrocyte sedimentation rate (ESR) or C-reactive protein (CRP). These tests are unnecessary as a clinical examination demonstrates the degree of infection
- As with any acute infection, it is not unusual to have slightly deranged liver transaminases (AST/ALT), if these happen to be tested
Other laboratory test findings
- If a Culture of purulent discharge is performed the results generally take 2-3 days. Cultures are of more value in cases with high MRSA levels in the community or in wounds which occurred from an unusual source such as a bite or another contaminated source
Radiographic findings
- In most cases, radiographs are not indicated
- X-rays can be a reasonable screening test if osteomyelitis is suspected. Expected findings consistent with osteomyelitis are lytic or periosteal changes
- X-rays may also be useful in cases of suspected gangrene/necrotizing fasciitis where air in the soft tissues may be demonstrated
- Ultrasonography can be utilized to evaluate for fluid collections such as abscess
- CT scan can be used to evaluate osteomyelitis and/or abscess (note that if the only suspicion is abscess, ultrasonograph-or clinical examination by an experienced clinician is most appropriate)
- MRI can be useful in evaluating necrotizing fasciitis and also to evaluate for osteomyelitis
- Contrast enhancement, thickening of deep fasciae with fluid collection (necrotizing fasciitis)
- Shows evidence of osteomyelitis if present
General treatment items
- Appropriate antibiotic therapy
- Immobilization and elevation of the involved limb
- Apply dressings over purulent draining lesions
- If an abscess is present, surgical drainage should occur along with flushing of all purulent matter from the abscess cavity with packing (small abscesses may not need packing so long as an adequate incision and drainage has been performed)
- Compression stockings in patients with lymphedema or other causes of peripheral edema
Pharmacological treatment If the patient is not up to date with their tetanus immunization, and a wound has led to cellulitis; it is reasonable to update this immunization.
Empiric treatment for cellulitis in mild to moderately ill patients It is reasonable to treat patients who are only mildly ill who have a proximal cellulitis with no other significant co-morbid conditions with oral antibiotics with close follow-up. In the event of significant comorbidities or in the event of moderate or distal infection (hand/foot), intravenous therapy may be indicated.
- Immunocompetent without specific etiology: First line therapy
- Upper or lower extremity: In low MRSA regions, first generation cephalosporins or second generation penicillins are reasonable. Examples of these agents include: cephalexin, cefadroxil, dicloxacillin, flucloxacillin, nafcillin, or cefazolin. Secondary choices include amoxicillin-clavulanate, clindamycin, macrolides such as azithromycin, or erythromycin
- Upper or lower extremity: If there is an increased MRSA risk, it is reasonable to cover MRSA in patients who are stable to be treated as outpatients. Options for oral therapy of Community Aquired MRSA (CA-MRSA) include:
- Trimethoprim/sulfamethoxazole (Bactrim/Septra)
- Doxycycline
- Minocycline
- Clindamycin
- Additionally, adequate streptococcal coverage should be supplied, generally with a first generation cephalosporin or second generation penicillin (as listed above)
- In cases of patients requiring admission intravenous options include vancomycin, clindamycin, daptomycin, linezolid, telavancin, tigecycline, or ceftaroline
- Facial cellulitis is most commonly caused by group A beta hemolytic streptococcus (GABHS), less commonly by Streptococcus pyogenes or Staphylococcus aureus. In mild cases antibiotic selection with no MRSA coverage is reasonable in low CA-MRSA areas. In cases of higher CA-MRSA risk, addition of CA-MRSA coverage is appropriate
- Diabetic foot ulcer: Therapy usually includes gram positive, gram negative and anaerobic coverage (Amoxicillin-Clavulanate, Cephalexin-Metronidazole are oral options; IV options include Ticarcillin-clavulanate, Ampicillin-sulbactam, Piperacillin-tazobactam, or other similar agents, 1st-3rd generation cephalosporins + metronidazole). MRSA coverage can be added in selected cases as appropriate
- Immunocompetent with specific etiology: First line therapy
- Bite-related (human, dog, cat): amoxicillin/clavulanate is the first line therapy. Options for second line therapy include ticarcillin-clavulanate or piperacillin-tazobactam. Other options include advanced (3rd/4th generation) fluoroquinolones + metronidazole. Other options include clindamycin or metronidazole + doxycycline or cefuroxime or trimethoprim- sulfamethoxazole for all bites (human, dog, or cat bites)
- Freshwater exposure: Penicillinase-resistant penicillins plus gentamicin or a fluoroquinolone
- Saltwater exposure: IV 1st generation cephalosporin such as cefazolin 1-1.5 gm IV q8h (max 12 gm/day) plus oral doxycycline 100 mg BID
- Immunocompromised: First line therapy
- Broad-spectrum gram-positive (including MRSA) antibiotic cover (primary choice: vancomycin or daptomycin or linezolid) plus Pseudomonas cover (primary choice: ceftazidime, imipenem/cilastatin, meropenem, or ciprofloxacin). Ticarcillin-clavulanate, ampicillin-sulbactam, or piperacillin-tazobactam are reasonable choices
Empiric treatment of cellulitis in the severely ill patients:- Immunocompetent: First line therapy: Parenteral antibiotic with MRSA (methicillin-resistant Staphylococcus aureus) coverage
- Primary choice: vancomycin
- Secondary choice: daptomycin or linezolid or telavancin
- Immunocompromised:
First line therapy: Parenteral antibiotic with MRSA coverage
- Primary choice: vancomycin
- Secondary choice: daptomycin or linezolid or telavancin
In addition to therapies listed above, severely ill patients may benefit from addition of coverage for Pseudomonas, with ceftazidime being the primary agent, with other potential options being ciprofloxacin, ticarcillin-clavulanate, piperacillin-tazobactam.
In the event the patient is not responding to initial therapy, consultation and review of culture results where obtained are indicated. Some patients will require surgical debridement.
Medications indicated with specific doses
- Amoxicillin-clavulanate
- Ampicillin-sulbactam
- Cefadroxil
- Cefazolin
- Ceftaroline
- Ceftazidime
- Cefuroxime (IV)
- Cefuroxime (Oral)
- Cephalexin
- Ciprofloxacin (Oral)
- Ciprofloxacin (IV)
- Clindamycin (Oral)
- Clindamycin (IV)
- Daptomycin
- Dicloxacillin
- Doxycycline (Oral)
- Doxycycline (IV)
- Gentamicin
- Imipenem/cilastatin
- Linezolid (Oral)
- Linezolid (IV)
- Meropenem
- Metronidazole (Oral)
- Metronidazole (IV)
- Minocycline
- Nafcillin
- Piperacillin-tazobactam
- Telavancin
- Ticarcillin-Clavulanate
- Tigecycline
- Trimethoprim/sulfamethoxazole
- Vancomycin
