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  • Cellulitis is a common bacterial skin infection, with over 14 million cases occurring in the United States annually. It accounts for approximately 3.7 billion dollars in ambulatory care costs and 650000 hospitalizations annually.

  • Cellulitis typically presents as a poorly demarcated, warm, erythematous area with associated edema and tenderness to palpation.

  • It is an acute bacterial infection causing inflammation of the deep dermis and surrounding subcutaneous tissue.

  • The infection is without an abscess or purulent discharge. Beta-hemolytic streptococci typically cause cellulitis, generally group A streptococcus (i.e., Streptococcus pyogenes), followed by methicillin-sensitive Staphylococcus aureus.

  • Patients who are immunocompromised, colonized with methicillin-resistant Staphylococcus aureus, bitten by animals, or have comorbidities such as diabetes mellitus may become infected with other bacteria. 


  • The skin serves as a protective barrier preventing normal skin flora and other microbial pathogens from reaching the subcutaneous tissue and lymphatic system.

  • When a break in the skin occurs, it allows for normal skin flora and other bacteria to enter into the dermis and subcutaneous tissue. 

  • The introduction of these bacteria below the skin surface can lead to an acute superficial infection affecting the deep dermis and subcutaneous tissue, causing cellulitis.

  • Cellulitis most commonly results from infection with group A beta-hemolytic streptococcus (i.e., Streptococcus pyogenes).

  • Risk factors for cellulitis include any culprit that could cause a breakdown in the skin barrier such as skin injuries, surgical incisions, intravenous site punctures, fissures between toes, insect bites, animal bites, and other skin infections.

  • Patients with comorbidities such as diabetes mellitus, venous insufficiency, peripheral arterial disease, and lymphedema are at higher risk of developing cellulitis.

Common Complaints:

  • Swelling. Tenderness.

  • Pain. Warmth. Pus

  • Fever. Chills. Red rash

  • Red spots. Skin dimpling

Treatments if recommended. 

Nonpurulent Cellulitis/Erysipelas.

  • Amoxicillin/Clavulanate 

  • Dicloxacillin 500 mg po 3 times a day. 

  • Cephalexin 500 mg po 4 times a day.

If MRSA suspected ADD:

  • Bactrim DS 

  • Clindamycin

  • Doxycycline

Freshwater exposure:

  • Doxycycline 100 

  • TMP/SMX (DS) 

Saltwater exposure:

  • Doxycycline

  • Levofloxacin 

Perirectal abcess:

  • Augmentin

  • Metronidazole

Recommend Ancillary therapies:

  • Tylenol/Ibuprofen for pain if not contraindicated.

  • Warm compresses 

  • Keep legs elevated 


  • Cellulitis is diagnosed clinically based on the presence of spreading erythematous inflammation of the deep dermis and subcutaneous tissue. It characteristically presents with worsening erythema, edema, warmth, and tenderness.

  • Two of the four criteria (warmth, erythema, edema, or tenderness) are required to make the diagnosis. Its most common presentation is on the lower extremities but can affect any area of the body.

  • It is most often unilateral and rarely (if ever) presents bilaterally. The patient's skin should be thoroughly evaluated to find the potential source for the cellulitis by looking for microabrasions of the skin secondary to injuries, insect bites, pressure ulcers, or injection sites. 

  • If cellulitis is affecting the patient's lower extremities, careful evaluation should be made to look between the patient's toes for fissuring or tinea pedis. Additionally, it can affect the lymphatic system and cause underlying lymphadenopathy. The associated edema with cellulitis can lead to the formation of vesicles, bullae, and edema surrounding hair follicles leading to peau d'orange. 

  • The Infectious Disease Society of America practice guidelines recommend against imaging the infected area except in patients with febrile neutropenia.

  • Consider blood cultures only in patients that are immunocompromised, experienced an immersion injury or animal bite.[9] Blood cultures are also necessary when a patient has signs of systemic infection.

More Treatment / Management:

  • Patients presenting with mild cellulitis and displaying no systemic signs of infection should be covered with antibiotics that target the treatment of streptococcal species. Though believed to be a less common cause, consider coverage of MSSA.


  • The duration of oral antibiotic therapy should be for a minimum duration of 5 days. In nonpurulent cellulitis, patients should receive cephalexin 500 mg every 6 hours. If they have a severe allergic reaction to beta-lactamase inhibitors, treat with clindamycin 300 mg to 450 mg every 6 hours.


  • In patients with purulent cellulitis, methicillin-resistant staph aureus colonization, cellulitis associated with an abscess or extensive puncture wounds, or a history of intravenous drug use, patients should receive antibiotics that cover against methicillin-resistant staph aureus as well.


  • Cellulitis with MRSA risk factors should be treated with trimethoprim-sulfamethoxazole 800 mg/160 mg twice daily for 5 days in addition to cephalexin 500 mg every 6 hours. If a patient has an allergy to trimethoprim-sulfamethoxazole, treat with clindamycin 300 mg to 450 mg every 6 hours. A longer duration of antibiotic treatment may be a consideration in patients who show minimal improvement with antibiotic therapy within 48 hours. 

  • Hospitalization with the induction of systemic antibiotics may be necessary for patients who: present with systemic signs of infection*, have failed outpatient treatment, are immunocompromised, exhibit rapidly progressing erythema, are unable to tolerate oral medications, or have cellulitis overlying or near an indwelling medical device.


  • Intravenous antibiotics should be initiated to cover against group A strep. Absent patient risk factors for MRSA, treat with intravenous cefazolin, and when able de-escalate to cephalexin for a total of 5 days of treatment. If risk factors for MRSA are present, initiate therapy with Vancomycin with subsequent de-escalation to trimethoprim/sulfamethoxazole.


  • In immunocompromised patients requiring hospitalization for parenteral antibiotics, broad-spectrum antimicrobial coverage may be necessary with vancomycin plus piperacillin-tazobactam or a carbapenem. 


  • The clinician should obtain blood cultures if a patient is exhibiting signs of systemic toxicity, has persistent cellulitis despite adequate treatment, has unique exposures such as animal bites or water-associated injuries.


  • Atypical organisms can cause cellulitis in particular situations. If exposed to a dog or cat bite, patients are at risk for developing cellulitis secondary to Pasteurella multocida. If secondary to an injury involving exposure to water, such as a cut from an oyster shell, cellulitis can be caused by Vibrio vulnificus.


  • Diabetic patients and patients with diabetic foot ulcers are at risk for Pseudomonas aeruginosa. Immunocompromised patients are at risk for Pseudomonas aeruginosa and Cryptococcus. 


  • If patients have significant edema with a known cause for the edema, the underlying condition should receive proper treatment to decrease the amount of edema and prevent future episodes of cellulitis. Patients should be instructed to keep the affected area elevated.


  • * Two or more of these systemic inflammatory response criteria: fever (over 38 degrees C), tachycardia (heart rate exceeding 90 beats/min), tachypnea (respiratory rate over 20 breaths/min), leukocytosis (white blood cells in excess of 12000/mm) leukopenia (white blood cells under 4000/mm) or bandemia greater than or equal to 10%.



Note: Fever greater than 101.0, vaginal Abscess, Breast abscess, calf swelling/pain, please go to the ER.



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