Chapter 90. Soft Tissue Infections

Patients with soft tissue infections present frequently to the emergency department (ED). The management of these infections involves an understanding of appropriate antibiotic treatment, outpatient or inpatient treatment options, and an understanding of when surgical intervention is necessary.

Community-acquired MRSA is epidemic across all populations. A significant majority of soft tissue infections in adults and children are caused by community-acquired MRSA. Understanding the treatment of community-acquired MRSA is vital for those managing soft tissue infections in the ED.

Clinical Features

Community-acquired MRSA is a frequent cause of skin and soft tissue infections. Lesions are typically warm, red, tender, and may be draining a purulent fluid. MRSA lesions are frequently mistaken as spider bites by patients as well and clinicians.

Diagnosis and Differential

The diagnosis of MRSA is largely clinical. Community-acquired MRSA should be considered in any infection where S aureus or Streptococcus is typically considered the etiologic agent. This includes skin and soft tissue infections as well as sepsis and pneumonia. Bedside ultrasound is helpful to identify abscess collections in equivocal cases.

Emergency Department Care and Disposition

1. For many community-acquired MRSA cutaneous infections, adequate incision and drainage (I&D) is adequate to manage these infections. Suggested criteria for withholding antibiotics include: abscesses that are small < 5 cm, abscesses in immunocompetent patients, and abscesses without accompanying cellulitis.

2. If local epidemiology supports MRSA as the likely etiology of cellulitis, antibiotics effective against MRSA should be given. These include clindamycin 300 milligrams PO 4 times daily or trimethoprim/sulfamethoxazole double strength 1 to 2 tablets twice a day for 7 to 10 days. Consider adding Cephalexin 500 milligrams 4 times daily to a regimen with trimethoprim/sulfamethoxazole to cover streptococcus. If the infection is severe, vancomycin 1 gram every 12 hours should be used, and inpatient therapy is indicated.

3. Patients who are at the extremes of age, have fever, significant comorbidities, or have a large number of lesions may require admission for parenteral antibiotics.

Necrotizing soft tissue infections are a spectrum of conditions that may be polymicrobial or monomicrobial. Group A Streptococcus and S aureus are often the etiologic agent in monomicrobial infections. Clostridial infections are now uncommon secondary to improved hygiene and sanitation.

Clinical Features

Patients present with pain out of proportion to physical findings and a sense of heaviness in the affected part. Physical findings typically include a combination of edema, brownish skin discoloration, bullae, malodorous serosanguineous discharge, and crepitance. The patient frequently has a low-grade fever and tachycardia out of proportion to the fever. Mental status changes, including delirium and irritability, may accompany necrotizing soft tissue infections.

Diagnosis and Differential

Familiarity with the disease and an appreciation of the subtle physical findings are the most important factors in making the diagnosis of necrotizing soft tissue infections. Additional findings that may confirm the clinical suspicion include gas within soft tissue on plain radiographs, metabolic acidosis, coagulopathy, hyponatremia, leukocytosis, anemia, thrombocytopenia, myoglobinuria, and renal or hepatic dysfunction.

Emergency Department Care and Disposition

1. The patient with necrotizing soft tissue infections should be adequately resuscitated with crystalloid intravenous (IV) fluids and packed red blood cells if there is significant hemolysis with anemia.

2. Urine output and central venous pressure readings should be used to assess volume status. Vasoconstrictors should be avoided in these patients because of compromised perfusion in the affected extremity.

3. IV antibiotics should be administered including vancomycin 1 gram IV every 12 hours plus meropenem 500 to 1000 milligrams IV every 8 hours. Alternatively piperacillin/tazobactam 4.5 grams IV every 6 hours may be used. The use of clindamycin should also be considered as it inhibits toxin synthesis.

4. Tetanus prophylaxis should be administered as indicated.

5. Surgical consultation for debridement should be obtained immediately and may include fasciotomy or amputation. Hyperbaric oxygen therapy and IV immunoglobulin therapy are controversial and typically the decision of the treating surgeon.

Cellulitis is a local soft tissue inflammatory response secondary to bacterial invasion of the skin. It is more common in the elderly, immunocompromised patients, and patients with peripheral vascular disease.

Clinical Features

Cellulitis presents as localized tenderness, erythema, and induration. Lymphangitis and lymphadenitis may accompany cellulitis and indicate a more severe infection. Patients may have fever and chills but are infrequently bacteremic.

Diagnosis and Differential

The clinical presentation is usually sufficient for diagnosis. Obtaining a white cell count or blood cultures rarely changes management of otherwise healthy patients with simple cellulitis. The differential diagnosis includes any erythematous skin condition. Cellulitis of the lower extremity is sometimes complicated by deep venous thrombosis and may require venogram or Doppler studies for a complete evaluation. In patients with systemic toxicity (fever and leukocytosis) cultures of pus, bullae or blood should be obtained.

Emergency Department Care and Disposition

1. Simple cellulitis in which MRSA is not suspected can be treated in an outpatient setting using cephalexin 500 milligrams PO 4 times daily, dicloxacillin 500 milligrams PO 4 times daily, or clindamycin 300 milligrams 4 times daily. If local epidemiology supports a high likelihood of MRSA in patients with soft tissue infections, antibiotics effective against MRSA should be given. In these cases clindamycin, trimethoprim/sulfamethoxazole, or doxycycline +/– cephalexin should be given.

2. All patients discharged should have close follow-up within 2 to 3 days to evaluate the cellulitis and response to therapy. Skin markers may be helpful to mark the extent of cellulitis in patients discharged from the ED.

3. All patients with systemic toxicity or evidence of bacteremia should be admitted to the hospital. Patients with diabetes mellitus, alcoholism, or other immunosuppressive disorders should be considered for admission for IV antibiotics.

4. IV antibiotics, such as clindamycin, vancomycin or linezolid, should be used in patients requiring hospital admission.

Erysipelas is a superficial cellulitis with lymphatic involvement caused primarily by group A Streptococcus. Infection is usually through a portal of entry in the skin.

Clinical Features

Onset is acute, with sudden high fever, chills, malaise, and nausea. Over the next 1 to 2 days, a small area of erythema with a burning sensation develops. The erythema is sharply demarcated from the surrounding skin and is tense and painful. Lymphangitis and lymphadenitis are common. Purpura, bullae, and necrosis may accompany the erythema. It is primarily an infection of the lower extremities.

Diagnosis and Differential

The diagnosis is based primarily on physical findings. Leukocytosis is common. Cultures, ASO titers, and anti-DNAase B titers are of little use in the ED. Differential diagnosis includes other forms of local cellulitis. Some believe necrotizing fasciitis is a complication of erysipelas and should be considered in all cases.

Emergency Department Care and Disposition

1. Treatment is with parenteral antibiotics active against streptococci including ceftriaxone 1 gram every 24 hours or cefazolin 1 to 2 grams every 8 hours. If it is difficult to distinguish between cellulitis and erysipelas, cover for S aureus as well as streptococci (see earlier). If the disease is severe, treat for MRSA with vancomycin, clindamycin, or linezolid and admit to the hospital.

2. Patients with mild disease may be treated with an initial dose of parenteral antibiotics and discharged on penicillin 500 milligrams PO every 6 hours. If the patient is allergic to penicillin a macrolide or cephalosporin may be used. Duration of treatment is 5 to 10 days and these patients should be reevaluated in 2 days for follow up.

Cutaneous abscesses are the result of a breakdown in the cutaneous barrier, with subsequent contamination with resident bacterial flora. Incision and drainage (I and D) is usually the only necessary treatment.

Clinical Features and Diagnosis

Patients present with an area of swelling, tenderness, and overlying erythema. The area of swelling is frequently fluctuant. Cutaneous abscesses are usually localized, although they may cause systemic toxicity in the immunosuppressed. Cutaneous abscesses should be inspected closely for predisposing injury and foreign bodies. Radiography may be indicated if foreign body is suspected. Needle aspiration or ultrasound may aid in the diagnosis when it is unclear whether the patient has an abscess or cellulitis.

Emergency Department Care and Disposition

1. See Chapter 7 for information on procedural sedation.

2. Bartholin gland abscess presents as unilateral painful swelling of the labia with a fluctuant 1 to 2 cm mass. These infections are typically polymicrobial, however, may contain Neisseria gonorrhoeae and Chlamydia trachomatis. Routine antimicrobial treatment is not necessary unless there is a suspicion of sexually transmitted disease. Treatment involves I&D along the vaginal mucosal surface of the abscess, generally followed by the insertion of a Word catheter. The Word catheter can be left in place for up to 4 weeks. Sitz baths are recommended after 2 days. Follow up with gynecology is recommended within 2 days in patients with severe symptoms and within one week in patients with mild symptoms.

3. Hidradenitis suppurativa is a recurrent chronic infection involving the apocrine sweat glands. These abscesses tend to occur in the axilla and in the groin. The causative organism is usually Staphylococcus, although Streptococcus also may be present. The abscesses are typically multiple and in different stages of progression. ED treatment involves I and D of any acute abscess, treating with antibiotics for any cellulitis that may be present, and referral to a surgeon for definitive treatment.

4. Infected sebaceous cysts may develop in the sebaceous glands, which occur diffusely throughout the skin. Cysts present with an erythematous, tender, cutaneous mass that is often fluctuant. I&D is the appropriate ED treatment, with wound rechecks in 2 to 3 days in the ED or physician's office. The cyst contains a capsule that must be removed to prevent recurrence. This capsule can sometimes be grasped at the time of the initial I&D however, this is typically done at a later follow-up visit.

5. Pilonidal abscess presents as a tender, swollen, and fluctuant mass along the superior gluteal fold. Treatment includes I&D followed by iodoform gauze packing. The patient should be rechecked in 2 to 3 days, and the wound should be repacked. Surgical referral is usually necessary for definitive treatment. Antibiotics are not necessary unless there is an accompanying cellulitis.

6. Staphylococcal soft tissue infection may cause folliculitis, the inflammation of a hair follicle caused by bacterial invasion, and is usually treated with warm compresses. When deeper invasion occurs, the soft tissue surrounding the hair follicle becomes infected, and a furuncle (boil) is formed. Warm compresses are usually adequate to promote spontaneous drainage. If several furuncles coalesce, they may form a large area of interconnected sinus tracts and abscesses called a carbuncle. Carbuncles usually require surgical referral for wide excision.

7. In the healthy, immunocompetent patient, routine use of antibiotics following abscess I&D is not indicated unless there is a secondary infection.

8. In the potentially immunocompromised patient, the threshold for antibiotic use should be lowered. Patients presenting with secondary cellulitis or systemic symptoms should be considered for antibiotic therapy. Abscesses involving the hands and face also should be treated more aggressively with antibiotics.

9. Prophylaxis for endocarditis in patients with structural cardiac abnormalities should be considered (see Chapter 93 for information on those at risk).

Sporotrichosis is caused by traumatic inoculation of the fungus Sporothrix schenckii, which is found on plants and in the soil.

Clinical Features

After a 3-week incubation period, 3 types of infection may occur. The fixed cutaneous type occurs at the site of inoculation and looks like a crusted ulcer or verrucous plaque. The local cutaneous type also remains at the site of inoculation but presents as a subcutaneous nodule or pustule. The surrounding skin may become erythematous. The lymphocutaneous type is the most common of the three. It presents as a painless nodule at the site of inoculation that develops subcutaneous nodules that migrate along lymphatic channels.

Diagnosis and Differential

The diagnosis is based on the history and physical examination. Tissue biopsy cultures are often diagnostic but of limited use in the ED. The differential diagnosis includes tuberculosis, tularemia, cat-scratch disease, leishmaniasis, nocardiosis, and staphylococcal lymphangitis.

Emergency Department Care and Disposition

1. Itraconazole 100 to 200 milligrams/d PO for 3 to 6 months is highly effective when treating sporotrichosis.

2. If disseminated, sporotrichosis may be treated with IV amphotericin B 0.5 milligram/kilogram/d.

3. Most cases of cutaneous sporotrichosis can be treated on an outpatient basis. Those patients who have systemic symptoms or who are acutely ill should be admitted for possible treatment with amphotericin B.