Soft tissue infections

OVERVIEW: What every practitioner needs to know

Are you sure your patient has a Soft Tissue Infection? What are the typical findings for this disease?

The most common manifestations of soft tissue infections, whether they are superficial or deep, include:

Erythema
Tenderness
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Induration
Warmth
Fluctuance

Superficial Infections: Cellulitis and Erysipelas

Cellulitis is an infection of the dermis and subcutaneous tissues and is typically characterized by warmth, erythema, tenderness, and induration. Often a punctum or area of traumatic inoculation can be identified. Erysipelas is a superficial infection characterized by an irregularly-shaped, raised, well-demarcated, erythematous, often progressive rash associated with fever and signs of systemic illness.

Deep Infections: Skin Abscess

Skin abscesses are defined by the presence of a fluid collection, and fluctuance can usually be demonstrated on exam. Similar characteristics of cellulitis may also be present, particularly induration, erythema, and tenderness.

Associated Symptoms

Other symptoms that may be present in the setting of soft tissue infections include fever, malaise, chills, and regional lymphadenopathy.

What other disease/condition shares some of these symptoms?

More superficial soft tissue infections, such as cellulitis and erysipelas, have signs and symptoms similar to those of insect bites, allergic or contact dermatitis, urticaria, atopic dermatitis, erythema migrans (Lyme disease), and erythema multiforme.

Skin abscesses, which present with areas of fluctuance and central pustules, may mimic lymphadenitis, spider bites, and hidradenitis suppurativa.

What caused this disease to develop at this time?

Soft tissue infections are typically produced by bacterial infection from Staphylococcus aureus or group A beta-hemolytic streptococci.
In cases of cellulitis, overwhelmingly, direct trauma to the skin is the most common mechanism, although hematogenous spread and associated bacteremia should be considered in neonates. Common exposures include broken skin from insect bites and skin abrasions. Careful history and examination may demonstrate evidence of potential traumatic introduction. For example, skin abrasions occurring on turf fields are a common predisposing mechanism for athletes.
Erysipelas, similar to cellulitis, may result from introduction of group A beta-hemolytic streptococci through breaks in the skin or in nearby sites.
Deeper skin abscesses often result from traumatic introduction of bacteria, followed by an inflammatory reaction, loculation of purulent material, followed by focal necrosis.
Predisposing factors for development of soft tissue infections also include diseases of the skin (e.g., atopic dermatitis, hyper-IgE syndrome), immune deficiency (congenital and acquired), corticosteriod use, diabetes mellitus, and lymphatic insufficiency.

What laboratory studies should you request to help confirm the diagnosis? How should you interpret the results?

In the acute setting, laboratory studies are rarely helpful in the evaluation of soft tissue infections. The most useful diagnostic measure is isolation and susceptibility testing of the offending bacterium in culture to assist in directing appropriate antimicrobial therapy in both the outpatient and inpatient setting.
For skin abscess, bacterial cultures are easily obtained through spontaneous drainage, or via surgical incision and drainage.
Isolation of organisms in cellulitis by needle aspiration of the inflamed soft tissue is more difficult and has a yield of less than 20%. Although not often performed, methods of bacterial isolation from cellulitis include fine-needle aspiration of the point of maximal inflammation or leading edge of the lesion.
Bacterial cultures from punch biopsy specimens should be considered in immunocompromised patients with cellulitis when the infection is not responding to the prescribed therapy or when less typical organisms (e.g., molds) are suspected.
The yield of blood cultures in soft tissue infections is exceedingly low. Therefore, blood cultures are not recommended in typical cases. Blood cultures should be considered in patients with malignancy, severe systemic features (e.g., hypotension), and unusual predisposing factors (e.g., neutropenia).

Would imaging studies be helpful? If so, which ones?

Ultrasonography, though not routinely required, has proven to be the most helpful imaging modality and diagnostic tool for characterization of soft tissue infections. Ultrasound can readily distinguish cellulitis from skin abscess through identification of fluid collection, which may inform decisions to perform incision and drainage. When available and in experienced hands, ultrasound can be of benefit at the bedside when performed by emergency physicians.
Magnetic resonance imaging (MRI) can be of benefit when the diagnosis of large, severe infections is unclear, such as when an underlying myositis, osteomyelitis, or necrotizing fasciitis is suspected.

Confirming the diagnosis

At present, no validated or published clinical algorithms exist for diagnosis of skin and soft tissue infections. Large-scale studies are currently being performed to better delineate optimal methods of diagnosis and indications for specific antibiotic therapies.

If you are able to confirm that the patient has a Soft Tissue Infection, what treatment should be initiated?

Indications for Hospitalization and Inpatient Therapy

Indications for inpatient admission of patients with soft tissue infections include the presence of systemic toxic appearance and clinical instability (e.g., hypotension).
Erysipelas: As a result of its typical rapid progression and systemic toxicity, children with this infection often require admission and treatment with intravenous antibiotic therapy for group A beta-hemolytic streptococci, including penicillins, first-generation cephalosporins, and clindamycin.
Cellulitis can often be managed as an outpatient; however, consideration should be given for hospitalization and intravenous therapy in the following cases:

Younger age

High fever

Facial location

Large size of the lesion

Rapid spread of the infection
Skin Abscesses should be incised and drained when possible. Similar to cellulitis, absolute indications for inpatient therapy and intravenous antibiotics do not exist. Consideration for hospitalization should be given for:

Younger age

High fever

Large size of lesion
Inpatient antibiotic options for cellulitis and skin abscesses are directed towards methicillin-sensitive and resistant S. aureus and group A beta-hemolytic streptococcus, specifically intravenous clindamycin. Trimethoprim-sulfamethoxazole appears to be effective for treatment of methicillin-resistant S. aureus (MRSA), but it is not effective for treatment of group A beta-hemolytic streptococcal infection. For refractory cases, or patients who are toxic-appearing, intravenous vancomycin has excellent systemic activity against all Gram-positive organisms.

Outpatient Therapy

Simple cellulitis is treated using oral antibiotics directed at both S. aureus and group A beta-hemolytic streptococci. Empiric antibiotics may include clindamycin or a first-generation cephalosporin.
For children with suspected erysipelas, specific treatment against group A beta-hemolytic streptoocci is indicated, typically a penicillin or first-generation cephalosporin.
When a skin abscess is present, the mainstay of therapy remains surgical incision and drainage and removal of purulent material. Drainage can often be performed in the emergency department, using local anesthesia and procedural sedation, when indicated. The decision for surgical consultation is at the discretion of the clinician. Recent evidence suggest that initial placement of topical anesthetic cream promotes spontaneous drainage in the ambulatory care setting, and may obviate the need for incision and drainage of small lesions.
The use of warm compresses several times a day can assist in promoting drainage of lesions.
The utility of adjuvant antibiotic therapy for skin abscesses, after incision and drainage remains in question. Clinicians wishing to prescribe antibiotics should ensure appropriate anti-staphylococcal coverage, particularly for community-associated MRSA (CA-MRSA) in high prevalence areas.
A 5-day course of antibiotics is recommended for typical infections when clinical improvement occurs within 4-5 days. A 10-day course can be considered in patients with slower clinical improvement or with more extensive infections.
Clinical follow-up within 48-72 hours is strongly recommended to assess clinical response to therapy and to assess for treatment failure.
A detailed list of outpatient antibiotic options for treating soft tissue infections is given below (Table I).

Table I.

Antibiotic	Advantages	Disadvantages
Clindamycin	Inexpensive, commonly CA-MRSA Active	Poor palatability; variable CA-MRSA resistance in some locales
Trimethoprim-Sulfamethoxazole	Inexpensive, excellent CA-MRSA activity	Poor group A streptococcal coverage
Cephalexin	Inexpensive, excellent activity against group A streptococcal and methicillin-susceptible S. aureus	Ineffective against CA-MRSA
Doxycyline	Inexpensive, widely available	Not recommended in children <8 years old; photosensitivity
Linezolid	Excellent CA-MRSA activity	Difficult to obtain; very expensive

Incision and Drainage

The mainstay of therapy for skin abscesses and other purulent skin infections, such as furuncles, is surgical incision and drainage. The procedure should be performed as follows:

Incision using a scalpel (e.g., 11-blade), approximately 1/2 to 2/3 the diameter of the fluctuance
Manual expression of purulent material
Wound culture of purulent material is recommended.
Debridement of wound cavity using a blunt instrument (e.g., hemostat) to lyse adhesions, followed by further manual expression
Complete wound packing is NOT recommended in children; for large wounds a “stent”, using a strip of iodoform gauze or Penrose drain may be used to keep wound open

What are the adverse effects associated with each treatment option?

The majority of antimicrobial therapies have few or rare adverse affects. All antimicrobials have the risk of allergic reaction, although beta-lactams (e.g., cephalexin) and sulfa drugs (e.g., trimethoprim-sulfamethoxazole) have a greater incidence of allergy. Clindamycin has been associated with an increased risk for developing enteritis from Clostridium difficile. Trimethoprim-sulfamethoxazole, as a result of its sulfa component, has been associated with development of the systemic inflammatory illness Stevens-Johnson syndrome.

What are the possible outcomes of Soft Tissue Infections?

With appropriate treatment, the outcome of soft tissue infections is typically excellent. Hematogenous spread of the bacterial infection is exceedingly rare, and the majority of soft tissue infections resolve with appropriate therapy.

In less than 5% of cases, superficial infections may not adequately respond to therapy, and progress to deeper skin abscesses, emphasizing the need for close follow-up.

What causes this disease and how frequent is it?

The predominant bacterial pathogens for soft tissue infections are the Gram-positive organisms Staphylococcus aureus and group A beta-hemolytic streptococci. Other common etiologic agents may produce infection in neonates (group B streptococci), and varying body sites, such as the genitourinary and buttock area (Gram-negative enterics) and axilla (Proteus mirabilis).
The incidence of soft tissue infections, particularly skin abscesses, has risen sharply in the previous decade, concomitant with the rise in prevalence of CA-MRSA across the United States.
Detailed epidemiology:

Skin and soft tissue infections are very common and can occur at any age, but most often affect toddlers and pre-school age children.

Introduction of the bacteria into the soft tissues typically occurs via one of three mechanisms: traumatic inoculation of the skin, direct extension of infection from a nearby focus (e.g., osteomyelitis), or from hematogenous spread from distant foci. Traumatic introduction from the skin surface is by far the most common mode of transmission.

The most common risk factors for development of soft tissue infection are related to the modes of transmission of S. aureus. These included crowding, contaminated and compromised skin surfaces, and frequent contact with other children. Pets may occasionally serve as reservoirs.

The genetics of predisposition to development of soft tissue infections is not well elucidated.

How do these pathogens/genes/exposures cause the disease?

S. aureus and other bacterial pathogens possess virulence factors, such as leukocidins, cell membrane toxins, and superantigens, that can initiate inflammation at the site of introduction. In turn, the host responses recruit defenses to fend off the infection, which involves additional inflammatory mediators and leukocyte chemotaxis. As the bacterial pathogen multiplies, the cycle of inflammation propagates and produces the clinical symptoms of soft tissue infection.
Interestingly, the rash of erysipelas may be produced by a toxin elicited from group A beta-hemolytic streptococci, while the site of actual inoculation may be from another location.

Other clinical manifestations that might help with diagnosis and management

N/A

What complications might you expect from the disease or treatment of the disease?

Complications from soft tissue infections are unusual. The overlying skin in afflicted individuals may not return to normal for days to weeks after the infection. In cases of skin abscesses, scarring may occur at the site of spontaneous drainage or surgical incision.

Rarely, soft tissue infections can directly extend into the deeper tissues, producing necrotizing fascitiis, a medical emergency.

Are additional laboratory studies available; even some that are not widely available?

The only proven laboratory study of utility for soft tissue infections is wound culture. Isolation of the pathogen in culture can assist in guiding appropriate antibiotics therapy, particularly in cases of clinical failure. Moreover, wound cultures permit surveillance of current antibiotic resistance patterns, particularly for methicillin resistance of S. aureus.

How can Soft Tissue Infections be prevented?

The most common organisms producing soft tissue infections are ubiquitous, and colonization of healthy individuals is extremely common. Therefore, prevention of soft tissue infection is difficult, as there are multiple factors that lead to the actual disease. The majority of prevention strategies are focused on hygiene, care for broken or compromised skin surfaces, and routine surveillance.

For patients who develop recurrent and frequent soft tissue infections from strains of S. aureus, decolonization protocols can be offered in conjunction with ongoing reinforcement of hygiene measures, although their efficacy and effectiveness are questionable. Therefore, clinicians should review the specifics of decolonization protocols used at their institutions. Typical components of eradication regimens include:

Intransal mupirocin 2-3 times daily for 1 week
Chlorhexidine solution for daily bathing or showering for 1 week

Some families prefer dilute “bleach baths:” Dilute clorox baths–1/4 cup of clorox in 1/4 tub of water (or 13 gallons of water) for 15 minutes twice weekly for 3 months

Adjunct oral antibiotic therapy is not routinely recommended for decolonization

Hygiene measures

Frequent hand washing

Avoidance of sharing personal care items such as towels or bed linens

Wash all sheets and towels in hot water weekly

Post-decolonization surveillance cultures are not recommended

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