Cellulitis : Definition, Symptoms, Treatment, and Complications
Bacterial infections of the skin can be classified as primary (pyodermas or cellulitis) or secondary (invasion of the wound). Primary bacterial infections are usually caused by a single bacterial species and involve areas of generally healthy skin (e.g., impetigo, erysipelas). Secondary infections, however, develop in areas of previously damaged skin and are frequently polymicrobic in nature.
The conditions that may predispose a patient to the development of skin and soft tissue infections (SSTIs) include (1) a high concentration of bacteria, (2) excessive moisture of the skin, (3) inadequate blood supply, (4) availability of bacterial nutrients, and (5) damage to the corneal layer allowing for bacterial penetration.
The majority of SSTISs are caused by gram-positive organisms and, less commonly, gram-negative bacteria present on the skin surface. Staphylococcus aureus and Streptococcus pyogenes account for the majority of SSTIs.
Cellulitis is an acute, spreading infectious process that initially affects the epidermis and dermis and may subsequently spread within the superficial fascia. This process is characterized by inflammation but with little or no necrosis or suppuration of soft tissue.
Cellulitis is characterized by erythema and edema of the skin. The lesion, which may be extensive, is painful and nonelevated and has poorly defined margins. Tender lymphadenopathy associated with lymphatic involvement is common. Malaise, fever, and chills are also commonly present. There is usually a history of an antecedent wound from minor trauma, an ulcer, or surgery.
A Gram stain of a smear obtained by injection and aspiration of 0.5 mL of saline (using a small-gauge needle) into the advancing edge of the erythematous lesion may help in making the microbiologic diagnosis but often yields negative results.
Acute cellulitis with mixed aerobic-anaerobic flora generally occurs in diabetes, where the skin is near a traumatic site or surgical incision, at sites of surgical incisions to the abdomen or perineum, or when host defenses are compromised.
- The goal of therapy of acute bacterial cellulitis is rapid eradication of the infection and prevention of further complications.
- Antimicrobial therapy of bacterial cellulitis is directed toward the type of bacteria either documented to be present or suspected.
- Local care of cellulitis includes elevation and immobilization of the involved area to decrease local swelling.
- As streptococcal cellulitis is indistinguishable clinically from staphylococcal cellulitis, administration of a semisynthetic penicillin (nafcillin or oxacillin) is recommended until a definitive diagnosis, by skin or blood cultures, can be made . If documented to be a mild cellulitis secondary to streptococci, oral penicillin VK, 250 to 500 mg four times daily for 7 to 10 days, or intramuscular procaine penicillin may be administered. More severe streptococcal infections should be treated with intravenous antibiotics (such as ceftriaxone 50 to 100 mg/kg as a single dose). Mild to moderate staphylococcal infections may be treated orally with dicloxacillin, 250 to 500 mg four times daily.
- In penicillin-allergic patients, oral or parenteral clindamycin may be used. Alternatively, a first-generation cephalosporin such as cefazolin (1 to 2 g intravenously every 6 to 8 hours) may be used cautiously for patients who have not experienced immediate or anaphylactic penicillin reactions and are penicillin skin test negative. In mild cases where an oral cephalosporin can be used, cefadroxil, 500 mg twice daily, or cephalexin, 250 to 500 mg four times daily, is recommended. Cefaclor, cefprozil, and cefpodoxime proxetil are effective but more expensive.
- Alternative agents for documented infections with resistant gram-positive bacteria such as methicillin-resistant staphylococci and vancomycin-resistant enterococci include linezolid, quinupristin/dalfopristin, and daptomycin. In severe cases in which cephalosporins cannot be used because of documented methicillin resistance or severe allergic reactions to Î²-lactam antibiotics, intravenous vancomycin should be administered.
- For cellulitis caused by gram-negative bacilli or a mixture of microorganisms, immediate antimicrobial chemotherapy as determined by Gram stain is essential, along with appropriate surgical excision of necrotic tissue and drainage. Gram-negative cellulites may be treated appropriately with an aminoglycoside or first- or second-generation cephalosporin. If gram-positive aerobic bacteria are also present, penicillin G or a semisynthetic penicillin should be added to the regimen. Therapy should be 10 to 14 days in duration.