Skin and Soft Tissue Infections

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184 Skin and Soft Tissue Infections

Ellen M. Slaven

• Uncomplicated subcutaneous abscesses in otherwise healthy patients require incision and drainage alone, without antibiotic therapy.

• Cellulitis with induration may harbor a deep purulent collection despite the lack of fluctuance on physical examination. Ultrasound or needle aspiration may be used to assist in the search for areas of pus that require incision and drainage.

• Cellulitis with purulence should be treated with antibiotics that are active against community-acquired methicillin-resistant Staphylococcus aureus (CA-MRSA), and cellulitis without purulence should be treated with antibiotics active against Streptococcus species.

• Patients with mild diabetic foot infections may be treated with oral agents that target gram-positive organisms, including CA-MRSA.

• Emergency physicians must always search for signs of necrotizing infection to exclude the deadly diagnosis early in the management of skin and soft tissue infections.

• Emergency consultation with a surgeon is mandated when a suspicion of necrotizing skin and soft tissue infection arises.

Community-Acquired Methicillin-Resistant Staphylococcus Aureus

Since the late 1990s, an epidemic of skin and soft tissue infections has been caused by community-acquired methicillin-resistant Staphylococcus aureus (CA-MRSA). Currently in the United States, CA-MRSA is the most common cause of skin and soft tissue infection in patients presenting to emergency departments. Patients who develop these infections have been previously healthy, and most have not been exposed to health care settings or prior antibiotic therapy.¹

CA-MRSA is distinguished from hospital-acquired MRSA (HA-MRSA) not only by the location of acquisition, but also by the type of infection produced. HA-MRSA causes wound infections, sepsis, endocarditis, and metastatic infections, but CA-MRSA causes predominantly purulent skin infections. HA-MRSA rarely carries the Panton-Valentine leukocidin that is believed to be a potent virulence factor found in most CA-MRSA strains. In addition, HA-MRSA is generally resistant to many antibiotics, whereas CA-MRSA tends to be resistant predominantly to β-lactam agents but remains susceptible to many other antibiotics, such as trimethoprim-sulfamethoxazole and the tetracyclines. Unfortunately, the designation of these staphylococcal strains based on the site of acquisition has led to confusion now that newly developed CA-MRSA infections have been increasingly identified within hospitals.

In 2011, the Infectious Disease Society of America released its long-anticipated first clinical guidelines for the treatment of MRSA infections, including CA-MRSA, in adults and children.¹ The panel of experts provided an evidence-based framework for the clinical evaluation and treatment of skin and soft tissue infections and more invasive infections such as bacteremia and pneumonia.

Superficial Skin Infections

Impetigo

Impetigo is most commonly encountered in preschool-age children. It is a superficial infection involving the epidermis and is highly contagious. Impetigo is readily spread from one site to another on one child and just as easily from one child to another. Two types of impetigo are recognized. The classic nonbullous impetigo begins with a vesicular lesion that becomes purulent. The vesicle then ruptures and reveals the typical, honey-colored crusted lesion. The face and extremities are commonly involved. Streptococcus pyogenes (group A Streptococcus) is the pathogen. The infection is self-limited and generally heals without scarring. Treatment is aimed at rapid resolution and prevention of transmission. The second type of impetigo, bullous impetigo, is caused by a toxin-producing strain of S. aureus. The appearance of bullous impetigo is of a flaccid, bullous lesion that may become filled with purulent fluid. Approximately 10% to 20% of all cases of impetigo are the bullous type.

Treatment with topical mupirocin is effective in patients with mild impetigo. Patients with more severe infections require systemic therapy with cephalexin for 7 days. Azithromycin (500 mg orally on day 1, then 250 mg orally on days 2 to 5) is an alternative for patients who are allergic to penicillin. Empiric therapy for CA-MRSA bullous impetigo should be reserved for patients in whom this standard treatment fails.

Erysipelas

S. pyogenes is the primary pathogen responsible for the intradermal infection known as erysipelas, or Saint Anthony’s fire. This infection also involves the lymphatic drainage of the skin and produces a bright, erythematous raised area of skin. It is very well demarcated. The diagnosis is based on clinical appearance. The rash is common in older persons and in young children. Seventy percent of infections occur on the lower leg, and approximately 20% of infections occur on the face. The onset is quite sudden, fever may be present, and the rash is frequently very painful.

The drug of choice is penicillin. Admission to the hospital for intravenous antibiotics and supportive care may be indicated for patients who suffer from serious comorbidities or for patients who appear toxic. Azithromycin is an alternative agent. Always examine the feet carefully for signs of fissuring and include topical antifungals for treatment of tenia pedis because fissures may be a portal of entry for streptococci.

Cellulitis

Cellulitis results from bacterial infection of the dermis and the subcutaneous fat. Infection may arise following the entry of bacteria into the dermis through small breaks in the skin, larger wounds, or preexisting dermatitis. The infection may be limited to a small patch, or it may spread to include extensive areas of skin. Cellulitis is manifested by erythematous, warm, tender regions of skin that frequently spread. Lymphangitis and lymphadenitis may be present. Fever, chills, and malaise are common associated symptoms.

The pathogens of cellulitis are rarely identified in any particular patient, but they are thought to be primarily S. pyogenes (less commonly, other β-hemolytic streptococci such as groups B, C and G) and S. aureus. Culture of material aspirated from the involved skin is not routinely performed because of the invasive nature of the procedure and the low diagnostic yield. Blood cultures are of little value; only approximately 2% to 5% of these cultures yield results. A newer distinction has been proposed between nonpurulent cellulitis, which is believed to be more likely caused by Streptococcus species, and cellulitis that is associated with purulence and is probably caused by S. aureus. (See the later discussion of purulent skin infections.)

Patients with mild cases of nonpurulent cellulitis may be treated on an outpatient basis with an antibiotic effective against Streptococcus species such as cephalexin or dicloxacillin. The precise length of therapy is determined by the patient’s response to therapy. A 5- to 10-day course of antibiotics is recommended. Empiric coverage for CA-MRSA should be reserved for patients who do not respond to β-lactam agents.

In patients with cellulitis who require hospital admission (e.g., those with extensive disease or underlying immunocompromises those who appear toxic), blood cultures are often obtained. Although the diagnostic yield of blood cultures is quite low, these cultures may provide useful information for patients who are significantly ill. Radiography may provide valuable information about patients with significant cellulitis, in particular to establish the presence of gas or foreign bodies. Patients with nonpurulent cellulitis who require admission may be treated with intravenous antibiotics, such as oxacillin, nafcillin, or cefazolin. For patients allergic to penicillin, azithromycin or levofloxacin may be substituted. Empiric coverage for CA-MRSA may be reserved for patients who do not improve during β-lactam therapy.

Purulent Skin Infections

Small, superficial pustular infections arising from the hair follicle are usually caused by S. aureus and are referred to as folliculitis. The lesions of folliculitis tend to be approximately 2 to 5 mm in diameter, they are isolated to the epidermis, and they generally produce pruritus rather than pain. Treatment consists of warm, moist compresses and topical antibiotic ointment, such as mupirocin. If systemic therapy is desired (because of a lack of response to topical therapy, extensive infection, or the presence of underlying immunocompromising medical condition), an agent active against CA-MRSA is recommended (Table 184.1).

Table 184.1 Antibiotics for Community-Acquired Methicillin-Resistant Staphylococcus aureus Skin Infections

DEGREE OF INFECTION	ANTIBIOTIC REGIMEN
Mild	Trimethoprim-sulfamethoxazole (double strength) 1 PO bid Clindamycin 300 mg PO qid Doxycycline 100 mg PO bid Buy Membership for Emergency Medicine Category to continue reading. Learn more here

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