Cellulitis
Cellulitis is a common infection caused by bacteria that affects the dermis and
subcutaneous tissue of the skin. It is frequently caused
by Staphylococcus aureus and Streptococcus pyogenes
. The skin infection presents as an erythematous and edematous area with warmth and
tenderness. The borders are not clearly delineated. The lower extremities are the most
frequent site of infection, but cellulitis can occur anywhere on the body. Diagnosis is
usually clinical, and management involves oral and/or parenteral antibiotics. Coverage
for MRSA may be added, depending on the presence of risk factors.
Last update:
March 4, 2021
7:17 am
Table of Contents
Overview
Pathophysiology and Clinical Presentation
Diagnosis
Management and Complications
Differential Diagnosis
References
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Overview
Definition
Cellulitis is inflammation of the skin and subcutaneous tissues. It is
often due to infection.
Epidemiology and etiology
Incidence: 200 cases per 100,000 patient-years
More common in middle-aged and older populations
Lower extremities: most common site
Most common agents:
o Staphylococcus aureus:
MSSA
MRSA
o Group A Streptococcus (Streptococcus pyogenes)
Less common agents:
o Pasteurella multocida (from animal bites)
o Aeromonas hydrophila and Vibrio vulnificus (after water
exposure)
o Clostridium species (myonecrosis)
o Pseudomonas aeruginosa (in immunocompromised
patients)
o Erysipelothrix rhusiopathiae (occupational exposure in
butchers, slaughterhouse workers, farmers, veterinarians)
Risk factors
Breach of the skin barrier (wounds, ulcers, insect/animal bites)
Skin inflammation (psoriasis, eczema)
Injuries contaminated with dirt or seawater
Preexisting infection (tinea, varicella)
Previous history of cellulitis
Crush injuries
Second- and third-degree burns
Frostbite
Lymphedema or any obstruction of lymphatic drainage
Immunodeficiency
Diabetes mellitus
Obesity
Venous insufficiency
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Pathophysiology and Clinical Presentation
Pathophysiology
Bacteria enter disrupted skin barrier:
o Through minor cuts or injuries
o May be secondary to a distant site or systemic infection
o In some cases, portal of entry is not evident.
Invasion of dermis and subcutaneous tissue triggers cytokine
release, recruiting neutrophils and other inflammatory cells to the
site.
Intrinsic bacterial factors allow the pathogen to evade initial host
defenses, leading to erythema, pain, and local swelling of
the skin (edema).
In immunocompromised patients, infection is limited eventually
to the area of invasion.
If the pathogen overcomes the immune defenses, further spread
(deeper and/or contiguous infection and bacteremia in
immunodeficiency) occurs.
Reduced control of infection occurs in:
o Decreased tissue vascularity and oxygenation
o Increased peripheral fluid stasis
o Poor ability to combat infections (e.g., diabetes)
Clinical findings
Prodromal systemic symptoms:
o May have signs of toxicity (fever > 100.5℉ (38℃), chills,
and tachycardia)
o Muscle and joint pain
o Headache
Local features:
o Indurated lesions or edematous area with erythema and
poorly defined borders
o Spreading redness or lesions
o Pain and tenderness in the affected area
o Tight, glossy, swollen skin or dimpling (noted
in edema surrounding hair follicles)
o May present with purulent exudate (usually associated
with S. aureus)
o An abscess may also be found (collection of pus within the
dermis or subcutaneous layer).
Associated signs and symptoms:
o Regional lymph node swelling and tenderness
(lymphadenitis)
o Severe infections:
Can present with general malaise, fatigue, dizziness,
confusion, muscle and joint pain, and diaphoresis
Can have blistering lesions or bullae formation
Diagnosis
Diagnosis of cellulitis is clinical:
o Edema
o Erythema
o Warmth
o Tenderness
o Associated lymphadenopathy
Symptoms, risk factors, and progression of the skin lesion aid in
ruling out differential diagnoses.
Laboratory tests are nonspecific:
o Leukocytosis (common in all infections)
o ↑ Inflammatory markers:
Erythrocyte sedimentation rate (ESR)
CRP levels
Microbiologic studies:
o Wound culture: used to identify pathogens and guide
antibiotic therapy
o Blood culture: obtained in cases suggestive of bacteremia
and/or in severely immunodeficient patients
Imaging:
o Ultrasonography (US) is used to rule out abscess.
o Complicated skin and soft tissue infections need to be
further evaluated.
Orbital and sinus CT to determine extent of orbital
cellulitis and presence of an abscess
MRI and/or bone scintigraphy may be performed in
cases of severe joint pain to confirm/rule out septic
arthritis or osteomyelitis.
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Management and Complications
Treatment approach
Supportive care:
o Symptomatic treatment for fever, local pain, and aches
o Adequate hydration and elevation of the affected lower limb
Empiric therapy covers group A Streptococcus and MSSA.
Determination of risk factors and need for parenteral therapy:
o MRSA risk factors:
Recent hospitalization or surgery (≤ 2 months ago)
Hemodialysis
Residence in a long-term care facility
HIV infection
Prior episode of MRSA
Recent antibiotic use without MRSA coverage
Indwelling medical device
o Need for parenteral therapy:
Inability to tolerate oral intake
Systemic signs of toxicity
Rapid progression of erythema
Cellulitis over a medical device (vascular graft or
prosthetic joint)
Failure to respond to prior oral antibiotics
Treatment regimen
No MRSA risk factors:
o Oral therapy (mild infection):
Dicloxacillin
Amoxicillin
Cephalexin
Clindamycin
o Parenteral therapy:
Cefazolin
Nafcillin
Oxacillin
Clindamycin
With MRSA risk factors:
o Oral therapy:
Trimethoprim–sulfamethoxazole
Amoxicillin plus doxycycline
Amoxicillin plus minocycline
Clindamycin
o Parenteral therapy:
Vancomycin
Daptomycin
Other considerations:
o Bite wounds: add anaerobic coverage
o Hospitalization:
Usually required for facial lesions because of high risk
of spread of infection to the CNS
(meningitis, encephalitis)
For those with concomitant conditions such as hepatic,
renal, or cardiac failure
o Severe progressive infections: might require surgical
debridement of necrotic tissue or abscesses
Cellulitis in the left lower leg and knee:
Left: Local swelling with salmon-pink skin discoloration and local warmth is evident.
Right: leg after 6 weeks of antibiotic therapy
Image: “Helicobacter cinaedi bacteremia with cellulitis in a living-donor kidney transplant recipient identified by matrix-
assisted laser desorption ionization time-of-flight mass spectrometry: a case report” by BMC Research Notes. License: CC
BY 4.0
Complications
Abscess:
o Collection of pus in the dermis or subcutaneous tissue
o Presents as a tender, fluctuant, erythematous swelling or
discrete nodule
o Treatment: incision and drainage of drainable abscess
detected on exam or US
Necrotizing fasciitis:
o Deep infection associated with rapid destruction and
necrosis of the fascia and subcutaneous tissues
o Life-threatening
Septic arthritis:
o Infection in a joint, frequently secondary to bacteria
o Develops from hematogenous seeding but can also arise
from extension of infection from the skin/soft tissue
Osteomyelitis:
Infection of the bone
o
o Poorly healing skin and soft tissue infections are at risk.
Sepsis:
o Potentially life-threatening organ dysfunction caused by a
dysregulated host response to infection
o Presentation can include fever, tachycardia,
tachypnea, hypotension, and/or altered mentation.
o Immunocompromised patients with skin infections are at
risk for this condition.
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Cellulitis
Differential Diagnosis
Erysipelas: an acute superficial infection of the upper dermis
and lymphatics, usually caused by group A beta-
hemolytic Streptococcus: This condition presents as a sharply
demarcated, raised skin lesion, with erythema, edema, and
warmth.
Necrotizing fasciitis: a rapidly progressive infection resulting in
extensive necrosis of subcutaneous tissue, fascia, and
muscle: Necrotizing fasciitis is most commonly caused by group
A Streptococcus but often involves other types of bacteria in a
mixed infection. The condition presents with necrosis, crepitus,
bullae, and purple skin discoloration.
Dermatitis: general term for edematous skin rash caused by an
allergic reaction, irritant, or infection
Folliculitis: a localized inflammation of the hair follicle or
sebaceous glands that is primarily caused by S. aureus:
Presentation includes erythema, papules, pustules, and
tenderness of the affected area.
Impetigo: a highly contagious skin infection of the upper
epidermis: Impetigo commonly affects children < 5 years of age
and is caused by S. aureus or group A Streptococcus. Patients
present with an erythematous area covered in small vesicles,
pustules, and/or honey-colored crusts.
Staphylococcal scalded skin syndrome Staphylococcal
Scalded Skin SyndromeStaphylococcal scalded skin syndrome (SSSS),
also known as Ritter disease and staphylococcal epidermal necrolysis, is a
toxin-mediated condition caused by Staphylococcus aureus. The exfoliative
toxin produced disseminates and cleaves desmoglein 1 in the epidermis,
causing separation and detachment of the skin.Staphylococcal Scalded
Skin Syndrome (SSSS) : a toxin-mediated blistering skin disorder
caused by S. aureus. Presentation includes diffuse cutaneous
erythema, tenderness, bullae formation, and superficial
desquamation (sloughing off of the superficial layer of skin,
leaving a red “scalded” appearance). The mucous membranes
are spared.
