A 4-year-old child presents with a fever and a red and swollen foot (Figure 126-1). The patient injured her foot 3 days ago by catching it in a door. On physical examination, the foot is warm, tender, red, and swollen, and the child's temperature is 39.4°C (103°F). The clinician diagnoses cellulitis and admits the child for IV antibiotics.
Cellulitis of the foot after an injury with a door in a 4-year-old girl. (Reproduced with permission from Richard P. Usatine, MD.)
Cellulitis is an acute infection of the skin that involves the dermis and subcutaneous tissues. Cellulitis causes erythema, swelling, warmth, and tenderness of the involved skin. Erysipelas is a specific type of superficial cellulitis with prominent lymphatic involvement leading to a sharply defined and elevated border (see Figure 126-6). Purulent cellulitis is defined as the presence of pustules, purulent drainage or an abscess within or adjacent to the cellulitis.
Cellulitis is a common skin infection, with more than 650,000 admissions per year in the United States alone.1,2
In the United States, an estimated 14.5 million cases annually of cellulitis account for $3.7 billion in ambulatory care costs.1,3
ETIOLOGY AND PATHOPHYSIOLOGY
Cellulitis often begins with a break in the skin caused by trauma, excoriations, a bite, or an underlying skin disease (e.g., psoriasis, eczema, tinea pedis, stasis dermatitis) (Figures 126-2, 126-3, 126-4).
Cellulitis and abscess of the finger after a clenched fist injury in which the patient cut his finger on the tooth of the man he assaulted. (Reproduced with permission from Richard P. Usatine, MD.)
Cellulitis of the foot of a diabetic person in which there is possible necrosis and gangrene of the second toe, requiring hospitalization and a podiatry consult. (Reproduced with permission from Richard P. Usatine, MD.)
Cellulitis in an older man with venous stasis dermatitis. (Reproduced with permission from Richard P. Usatine, MD.)
The most common causative organisms are Streptococcus species and Staphylococcus aureus.1
Unfortunately, cellulitis is difficult to culture from the skin, so we have few reliable data about the organisms based on direct culture of the cellulitis. If there is coexisting purulence, S. aureus is likely to be involved.
Data from blood cultures can be used to help us understand the microbiology of the most severe cases of cellulitis. That is because most routine cases of cellulitis do not result in bacteremia.
From a systematic review of bacteremia in cellulitis and erysipelas, the following data are available4:
For cellulitis, 7.9% of 1578 patients had positive blood cultures, of which 19% were Streptococcus pyogenes, 38% were other β-hemolytic streptococci, 14% were S. aureus, and 28% were Gram-negative organisms.4
For erysipelas, 4.6% of 607 patients had positive blood cultures, of which 46% were S. pyogenes, 29% were other β-hemolytic streptococci, 14% were S. aureus, and 11% were Gram-negative organisms.4
The high proportion of Gram-negative bacteria might be due to inclusion of immunocompromised patients and those with cirrhosis, exposure to aquatic injuries, or animal bites.4
After a cat or dog bite, cellulitis may be caused by Pasteurella multocida.
After saltwater exposure, cellulitis can be secondary to Vibrio vulnificus in warm climates (Figure 126-5). A Vibrio vulnificus infection can be especially deadly.
S. aureus is more likely to be the causative organism in purulent cellulitis. This was demonstrated in a study of 422 patients who presented with "purulent skin and soft tissue infections" to 11 emergency departments, in which skin surface swab cultures revealed methicillin-resistant S. aureus (MRSA) in 59% of patients, methicillin-sensitive S. aureus in 17%, and β-hemolytic streptococci in 2.6%.1,5
MRSA should be considered as the potential causative organism for purulent cellulitis in known high-risk populations, such as athletes, children, men who have sex with men, prisoners, military recruits, residents of long-term care facilities, individuals with previous MRSA exposure, and injection drug users.1,6
Fatal Vibrio vulnificus infection with widespread cellulitis and bullae. The violaceous bullae should be a red flag for this infection and/or necrotizing fasciitis. Even though the infection was identified early, the overwhelming sepsis resulted in death. (Reproduced with permission from Donna Nguyen, MD.)
In one meta-analysis, risk of non-purulent cellulitis of the leg was associated with7:
Previous cellulitis odds ratio (OR) 40
Coexisting wound OR 19
Current leg ulcers OR 14
Lymphedema/chronic leg edema OR 7
Excoriating skin diseases OR 4
Tinea pedis OR 3
Body mass index > 30 OR 2.47
Diabetes, smoking, and alcohol consumption were not found to be associated with an increased risk of cellulitis.7
In other studies, risk factors for acute and recurrent cellulitis include8,9:
Psoriasis OR 4
Diabetes OR 1.7
In a smaller case control study of recurrent lower extremity cellulitis in U.S. veterans, two physical factors—lower extremity edema and body mass index, one behavioral factor—smoking, and one demographic factor—homelessness, were significantly and independently associated with recurrent cellulitis.10
Rubor (red), calor (warm), tumor (swollen), and dolor (painful).
Can occur on any part of the body, but is most often seen on the extremities and face (Figures 126-1, 126-2, 126-3, 126-4, 126-5, 126-6, 126-7, 126-8). Periorbital cellulitis can be life-threatening (Figure 126-9). Perianal cellulitis can occur in children or adults (Figure 126-10).
Erysipelas of the central face that responded well to oral antibiotic therapy. (Reproduced with permission from Ernesto Samano Ayon, MD.)
Cellulitis of the leg in a 55-year-old man that developed after a minor abrasion and a long plane flight. Petechiae and ecchymoses are visible and not infrequently seen in cellulitis. (Reproduced with permission from Richard P. Usatine, MD.)
Ascending lymphangitis characterized by lymphatic streaking up the leg in a 55-year-old man with cellulitis. (Reproduced with permission from Richard P. Usatine, MD.)
Life-threatening staphylococcal periorbital cellulitis requiring operative intervention. (Reproduced with permission from Frank Miller, MD.)
Severe perianal cellulitis in an adult man. (Reproduced with permission from Jack Resneck Sr., MD.)
Cultures of blood or cutaneous aspirates, biopsies, or swabs are not routinely recommended.11 SORⒷ
Cultures of blood and cutaneous aspirates should be considered in patients with malignancy on chemotherapy, neutropenia, severe cell-mediated immunodeficiency, immersion injuries, or animal bites.11 SORⒸ
Abscess—An abscess with surrounding erythema can look like cellulitis or in fact be what we call "purulent cellulitis." The red and swollen area should be palpated for fluctuance and aspiration, and/or incision and drainage should be performed to determine if an abscess is present (Figure 126-11).
Deep vein thrombosis (DVT) can cause a red and swollen lower extremity. While it is rare for a patient with cellulitis or erysipelas to have a DVT as well, the diagnosis of DVT should be considered in patients with thromboembolic risk factors (e.g., hypercoagulable state from pregnancy, oral contraceptives, malignancy). If a DVT is under consideration, Doppler studies of the red and swollen lower leg should be ordered.
Venous stasis and lymphedema—both conditions lead to swelling and erythema of the lower extremities, and both can be associated with cellulitis. In this case, venous stasis dermatitis appears like cellulitis (see Figure 126-4) (see Chapter 54, Venous Insufficiency).
Allergic reactions—Allergic reactions to vaccines or bug bites may resemble cellulitis because of the erythema and swelling (Figure 126-12).
Acute gout—May resemble cellulitis if there is significant cutaneous inflammation beyond the involved joint (see Chapter 102, Gout).
Necrotizing fasciitis—Deep infection of the subcutaneous tissues and fascia with diffuse swelling, severe pain, and bullae in a toxic-appearing patient. It is important to recognize the difference between standard cellulitis and necrotizing fasciitis. Imaging procedures can detect gas in the soft tissues. Rapid progression from mild erythema to violaceous or necrotic lesions and/or bullae in a number of hours is a red flag for necrotizing fasciitis. The toxicity of the patient and the other physical findings should encourage rapid surgical consultation (see Chapter 128, Necrotizing Fasciitis).
Cellulitis and abscess of the neck and chest in a 2-year-old girl in Ethiopia. Incision and drainage of the fluctuance over the neck revealed pus. A drain was placed to allow the pus to continue to drain from the incision site. She was treated with IV ceftriaxone, and she survived. (Reproduced with permission from Richard P. Usatine, MD.)
Redness and swelling after a pneumococcal vaccine the day before in a 66-year-old woman. This allergic reaction looks like bacterial cellulitis. It resolved with oral diphenhydramine. (Reproduced with permission from Richard P. Usatine, MD.)
Outpatient therapy is recommended for patients who do not have sepsis, altered mental status, or hemodynamic instability.11 SORⒷ
Hospitalization is recommended if there is concern for a deeper or necrotizing infection, for patients with poor adherence to therapy, for infection in a severely immunocompromised patient, or if outpatient treatment is failing.11 SORⒷ
Patients with non-purulent cellulitis without systemic signs of infection should receive an antimicrobial agent that is active against streptococci and methicillin-susceptible S. aureus (MSSA), such as oral cephalexin or oral dicloxacillin 500 mg four times a day for a minimum of 5 days.11 SORⒷ
The recommended duration of antimicrobial therapy is 5 days, but treatment should be extended if the infection has not improved within this time period.11 SORⒷ
Patients with cellulitis and systemic signs of infection such as fever should receive systemic antibiotics such as ceftriaxone IM and should be considered for hospitalization for IV antibiotics.11 SORⒷ
If there is significant purulence, incision and drainage should be performed.11 SORⒷ Consider oral antibiotics if there is an extension of the erythema and swelling beyond the abscess; then coverage against MSSA may be sufficient.11 SORⒸ
For patients whose cellulitis is associated with penetrating trauma, evidence of MRSA infection elsewhere, nasal colonization with MRSA, injection drug use, or sepsis, IV vancomycin in the hospital may be the treatment of choice.11 SORⒷ
If MRSA is suspected and the patient is stable for outpatient treatment, appropriate oral antibiotics include trimethoprim-sulfamethoxazole (TMP-SMX), doxycycline, minocycline, and clindamycin.11 SORⒷ
One randomized controlled trial (RCT) found no significant difference between clindamycin and TMP-SMX, with respect to either efficacy or side-effect profile, for the treatment of uncomplicated skin infections, including both cellulitis and abscesses. The study involved 524 patients including 155 children (29.6%). One hundred sixty patients (30.5%) had an abscess, 280 (53.4%) had cellulitis, and 82 (15.6%) had mixed infection, defined as at least one abscess lesion and one cellulitis lesion. S. aureus was isolated from the lesions of 217 patients (41.4%); the isolates in 167 (77.0%) of these patients were MRSA.13
In severely compromised patients, broad-spectrum intravenous antimicrobial coverage may be considered.11 SORⒸ Vancomycin plus either piperacillin-tazobactam or imipenem/meropenem is recommended as an empiric regimen for such severe infections. SORⒸ
Identify and treat predisposing conditions such as edema, obesity, eczema, psoriasis, lymphedema, venous insufficiency, and interdigital infections.11 SORⒷ
Elevation of the affected area and treatment of predisposing factors, such as edema or underlying cutaneous disorders, are recommended.11 SORⒷ
In lower-extremity cellulitis, clinicians should carefully examine the interdigital toe spaces for fissuring, scaling, or maceration, which may be caused by tinea pedis (see Chapter 146) and/or erythrasma (see Chapter 125). Treating these pathogens may reduce the incidence of recurrent infection. SORⒶ
Systemic corticosteroids (e.g., prednisone 40 mg daily for 7 days) could be considered in nondiabetic adult patients with cellulitis.11 SORⒸ
Clinicians should consider the treatment of modifiable risk factors including leg edema, wounds, ulcers, areas of skin breakdown, and tinea pedis while administering antibiotic treatment for non-purulent cellulitis of the leg.7 SORⒷ
Given the low reported overall incidence of DVT, neither routine prophylactic anticoagulation nor systematic paraclinical investigation for DVT is indicated in low-risk patients with erysipelas or cellulitis of the lower extremities. DVT should still be considered in patients with high pretest probability or other thromboembolic risk factors.14 SORⒷ
Preventing cellulitis and recurrent cellulitis:
Identify and treat predisposing conditions such as edema, obesity, eczema, psoriasis, lymphedema, venous insufficiency, and interdigital infections to prevent cellulitis and recurrent cellulitis.7,8,11 SORⒶ
When patients have recurrent cellulitis despite attempts to treat or control predisposing factors, then prophylactic antibiotics should be considered. A systematic review supports the use of oral penicillin VK or erythromycin twice daily in patients with recurrent cellulitis.15 Meta-analysis of 5 RCTs showed that antibiotic prophylaxis reduced the risk of recurrent cellulitis by approximately 50%.15 Antibiotics should be continued as long as the predisposing factors persist.11,15 SORⒶ
If the patient is immunocompetent without major risk factors and the case is uncomplicated, the prognosis for rapid and full recovery is excellent. However, patients who are immunocompromised and bacteremic with less common organisms are at risk for severe and fatal outcomes without rapid and aggressive treatment. Be careful to not miss necrotizing fasciitis, as this is life and limb threatening (see Chapter 128).
If prescribing oral outpatient therapy, consider follow-up in 2 days to assess response to the antibiotic and to determine the adequacy of outpatient therapy. If cultures are performed, make sure that the patient is on an appropriate antibiotic.
During treatment for cellulitis of an extremity, patients should elevate the involved extremity. If outpatient therapy is pursued, make sure the patient understands that an inability to tolerate the oral antibiotic is indication for seeking immediate care. Explain to the patient what their risk factors for cellulitis include. Include them in the treatment plan so that they may attempt to alter modifiable risk factors for the prevention of recurrent cellulitis. This often involves weight loss through a healthy lifestyle with good diet and exercise.
Executive Summary: Practice Guidelines for the Diagnosis and Management of Skin and Soft Tissue Infections: 2014 Update by the Infectious Diseases Society of America—http://cid.oxfordjournals.org/content/59/2/147.long.
A predictive model for diagnosis of lower extremity cellulitis: A cross-sectional study. J Am Acad Dermatol. 2017;76(4):618-625.
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et al. Risk factors for nonpurulent leg cellulitis: a systematic review and meta-analysis. Br J Dermatol.
et al. Recurrent cellulitis with benzathine penicillin prophylaxis is associated with diabetes and psoriasis. Eur J Clin Microbiol Infect Dis.
et al. Risk factors of cellulitis in cirrhosis and antibiotic prophylaxis in preventing recurrence. Ann Gastroenterol.
AL. Risk factors for recurrent lower extremity cellulitis in a U.S. Veterans Medical Center population. Am J Med Sci.
et al; Infectious Diseases Society of America. Practice guidelines for the diagnosis and management of skin and soft tissue infections: 2014 update by the Infectious Diseases Society of America. Clin Infect Dis.
S. Point-of-care ultrasound for diagnosis of abscess in skin and soft tissue infections. Acad Emerg Med.
et al; DMID 07-0051 Team. Clindamycin
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