History and exam

Key diagnostic factors

common

skin discomfort

Skin is usually very painful with redness, warmth, and swelling. A lower limb is the most common site of involvement.[1][12]​​

macular erythema

Macular erythema with tenderness, warmth, and edema are suggestive of the diagnosis.[1][12]​​ Cellulitis may have a well-demarcated or more diffuse border.[13][31]

disruption of cutaneous barrier

Leg ulcers, wounds, dermatoses, and tinea pedis interdigitalis all can be mechanisms of microorganism entry into the skin.[21]

raised bright-red erythema with clearly demarcated margins (erysipelas)

Erysipelas is a distinct form of superficial cellulitis with a raised, sharply demarcated edge distinguishing it from uninvolved skin.[1][12]​​[13] Typically affects the face and leg.[35]

risk of infection with MRSA

Infection with MRSA should be considered in patients with recent contact with a healthcare facility or if purulent skin disease is present (or has recently been present) in the patient or their close contacts. Groups that have been identified as having increased risk for infection with community-acquired MRSA include incarcerated individuals, intravenous drug users, military personnel, and athletic team members.[21]​[29][30]​​

Other diagnostic factors

common

history of diabetes

May predispose the patient to diabetic foot ulcers, which can be complicated by cellulitis.[13] For detailed information about diabetic foot infections, see our topic "Diabetic foot infections". 

uncommon

constitutional prodrome

Fever and chills occur in a minority of patients.[1][12]​​ However, systemic symptoms appear to be more common in patients with preexisting lymphatic insufficiency.[26] Fever, tachycardia, confusion, hypotension, and leukocytosis are sometimes present and may occur hours before the skin abnormalities appear.[13]

lymphangitis/regional lymphadenopathy

May present in cellulitis and is a common factor in erysipelas.[13][33]

Identifiable port of entry

A wound, ulcer, or signs of tinea infection, and local or regional lymphadenopathy, may be present.[36]

history of immunocompromise

In addition to the organisms causing cellulitis in an immunocompetent patient, immunocompromised patients are more susceptible to infections by aerobic gram-negative bacteria (e.g., Pseudomonas aeruginosa) and nonbacterial pathogens (e.g., Cryptococcus neoformans).[1][12]​​[13]

unusual exposure (salt or fresh water, bite)

May result in infection with an unusual pathogen.[1][12]​​[13]

Risk factors

strong

prior episode of cellulitis

Found as independent risk factor in prospective evaluation and case-control studies.[20][21] Recurrence is well documented and probably occurs due to persistence of other risk factors, such as lymphedema, but inflammation with each acute episode may also lead to residual lymphatic dysfunction.[14][22]

diabetes

Infections can occur when bacteria breach the skin surface, particularly where there is fragile skin or decreased local host defences.[13][23]

For detailed information about diabetic foot infections, see our topic "Diabetic foot infections".

ulcer/wound

Independent predictor of cellulitis in several studies.[20][21] Disruption of cutaneous barrier allows microorganism entry into tissue.

dermatosis

Independent predictor of cellulitis in a number of studies.[20][21]​​[22]​​ Disruption of cutaneous barrier allows microorganism entry into tissue.

tinea pedis interdigitalis

Independent risk factor for development of cellulitis.[20][21] Disruption of cutaneous barrier allows microorganism entry into tissue.[14] Pathogenic bacteria can be isolated from interdigital spaces in patients with tinea pedis interdigitalis.[19]

lymphedema

Lymphedema, often following surgery and/or radiation therapy for a malignancy, has been associated with cellulitis in several settings, including lymph node dissection with or without irradiation for breast and gynecologic cancers.[21]​[24][25]​​[26] The lymphatic impairment presumably renders local host defenses less effective, leading to subsequent infection.[14]

venous insufficiency/chronic leg edema

Cellulitis following saphenous venectomy is a well-recognized association.[20][27] Chronic edema resulting from other mechanisms also increases risk for cellulitis.[21] It is thought that the stasis of fluid reduces local host defenses, leading to infection.

weak

overweight

Increased BMI has been shown to be a risk factor in multivariate analyses of cellulitis.[20][21] This is presumed to be due to its association with reduced venous and lymphatic drainage.

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