The approach to common skin and soft tissue infections (SSTIs) was previously well understood. However, the recent emergence of community-associated methicillin resistant Staphyloccocus aureus as a common pathogen has changed the epidemiology of these infections and has led clinicians to alter their practice and treatment of SSTI. This article discusses the present epidemiology of SSTI and community-acquired methicillin-resistant Staphylococcus aureus , evidence-based approach to incision and drainage, the utility of adjuvant antibiotic therapy after abscess drainage, and current antimicrobial approach to cellulitis and nondrained SSTIs. Methods to reduce transmission and recurrence of SSTI through decolonization strategies are also discussed.
Key points
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The incidence of skin and soft tissue infections has rapidly increased in the previous decade, concomitant with the emergence of community-acquired methicillin-resistant Staphylococcus aureus (CA-MRSA) as a pathogen.
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The mainstay of therapy for skin abscesses remains incision and drainage; the role of wound packing and adjuvant antibiotics appears to be diminishing.
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Systemic antibiotics are indicated for treatment of cellulitis, and group A streptococcus remains a primary pathogen in this infection; the role of CA-MRSA is unknown.
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Bedside ultrasonography is superior to clinical examination in diagnosis of skin infections, and use of this modality improves emergency department management.
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The link between Staphylococcus aureus colonization and infection is unclear, although decolonization using a multifaceted approach may be used in cases of recurrent household infection.
Introduction
Infections of the skin and soft tissues are frequently encountered in ambulatory settings such as the emergency department (ED) and primary care offices. Skin and soft tissue infections (SSTIs) encompass a wide range of severity, from impetigo to fulminant “flesh-eating” invasive infection, better known as necrotizing fasciitis. However, the predominant skin infections encountered by pediatric practitioners include cutaneous abscesses and cellulitis. This article focuses on the current status of the ambulatory management of these 2 infections, as more benign infections such as impetigo, pustulosis, and folliculitis are less challenging for the clinician, and discussion of invasive infections are beyond the scope of this article.
A cutaneous, or skin abscess, is defined as a focal, contained, purulent infection with a clear “cavity” and surrounding inflammation involving the deep subcutaneous tissues. On physical examination, abscesses are typically tender, indurated, erythematous, and fluctuant. Fluctuance is a sign of purulence within the abscess cavity, although in some cases this finding may be difficult to detect, owing to induration and depth of the lesion. Occasionally, a pustule may be visible at the “point” of the abscess when the cavity is close to the skin surface; this pustule may erupt and produce spontaneous drainage of pus from the lesion ( Fig. 1 ). Mild systemic symptoms may be present in the setting of cutaneous abscess, including fever and malaise; toxicity is rare.
Cellulitis is pyogenic infection of the skin without an organized cavity and is typically limited to the epidermis, dermis, and superficial subcutaneous tissues ( Fig. 2 ). The hallmark physical findings of cellulitis include erythema, warmth, induration, and tenderness, although all criteria need not be present to make the diagnosis. In most cases, the margins of the infection are ill defined, although well-demarcated margins occur in group A streptococcal erysipelas. Cellulitis may present with fever and malaise, and severe toxicity is exceedingly uncommon. Clinical parameters of cellulitis overlap with skin abscess, because these infections lie within a spectrum; cases of cellulitis may evolve into abscess, and nearly all skin abscesses have some component of cellulitis immediately surrounding the abscess cavity. As a result of this overlap, SSTI diagnosis and treatment is challenging.
Microbiology
Most SSTIs result from infection with gram-positive cocci, specifically Staphylococcus aureus and group A streptococci. Although typical commensal organisms of the skin, bacteria infect the skin and soft tissues via direct inoculation, typical through disruption of the skin barrier. Proliferation of bacteria and development of cellulitis or abscess do not occur in a predictable fashion, and the clinical differentiation of superficial and dermal involvement versus presence of an abscess cavity may be difficult. Gram-negative organisms may also infect the skin and soft tissues, particularly in the buttock and axillary regions. Anaerobic bacteria are not typically present in cellulitis but are commonly implicated in necrotizing fasciitis as coinfecting organisms with S. aureus or group A streptococci.
Epidemiology and Emergence of CA-MRSA
In the United Sates, the incidence of SSTIs among the pediatric population has increased substantially in the previous 15 years. This upsurge is concomitant with emergence of community-associated strains of methicillin-resistant Staphylococcus aureus (CA-MRSA). Different from previous “hospital-acquired” or nosocomial strains (HA), CA-MRSA is a genetically distinct organism. The genes coding for methicillin resistance lie within the staphylococcal chromosomal cassette, or SCC mec gene, of which there are 4 predominant types. SCC mec type IV codes for CA-MRSA, and is a small, mobile genetic element, which facilitates transfer of methicillin resistance more readily than the larger elements coding for hospital-acquired methicillin-resistant Staphylococcus aureus (HA-MRSA). Clinical manifestations also differ, as CA-MRSA most commonly presents as skin infections, whereas HA-MRSA produces invasive infections, such as pneumonia and sepsis. It should be noted that the terms of “community” and “hospital” strains have become blurred, because CA-MRSA has been increasingly implicated in hospitalized and chronically ill populations.
Among SSTIs, cutaneous abscesses have had the most demonstrable increase in the era of CA-MRSA. Previously, skin abscesses were a result of methicillin-sensitive strains of S. aureus (MSSA); isolation of CA-MRSA from abscesses has since far surpassed that of MSSA. Because wound cultures are readily available after drainage, the microbiology of skin abscesses is well established, allowing for accurate epidemiologic surveillance. In the United States, the prevalence of CA-MRSA from cultured lesions is nearly universally greater than 50% and is as high as 70% to 80% in municipalities such as Chicago, Houston, and San Francisco.
Although great attention has been paid to CA-MRSA and SSTI in the United States, descriptions of CA-MRSA are occurring worldwide. The CA-MRSA strain ubiquitous across the United States were derived from the precursor strain USA300, although others are present around the world. Recent surveillance data have revealed that CA-MRSA is present on 6 continents and that prevalence in areas of Europe and South America rival that of the United States. In fact, analysis of CA-MRSA isolates across the Atlantic Ocean and Pacific Ocean have shown conservation of highly expressed virulence factors, such as Panton-Valentine leukocidin. Although CA-MRSA is present across the globe, similar dramatic increases in the incidence of SSTI as in the United States have yet to be documented.
Introduction
Infections of the skin and soft tissues are frequently encountered in ambulatory settings such as the emergency department (ED) and primary care offices. Skin and soft tissue infections (SSTIs) encompass a wide range of severity, from impetigo to fulminant “flesh-eating” invasive infection, better known as necrotizing fasciitis. However, the predominant skin infections encountered by pediatric practitioners include cutaneous abscesses and cellulitis. This article focuses on the current status of the ambulatory management of these 2 infections, as more benign infections such as impetigo, pustulosis, and folliculitis are less challenging for the clinician, and discussion of invasive infections are beyond the scope of this article.
A cutaneous, or skin abscess, is defined as a focal, contained, purulent infection with a clear “cavity” and surrounding inflammation involving the deep subcutaneous tissues. On physical examination, abscesses are typically tender, indurated, erythematous, and fluctuant. Fluctuance is a sign of purulence within the abscess cavity, although in some cases this finding may be difficult to detect, owing to induration and depth of the lesion. Occasionally, a pustule may be visible at the “point” of the abscess when the cavity is close to the skin surface; this pustule may erupt and produce spontaneous drainage of pus from the lesion ( Fig. 1 ). Mild systemic symptoms may be present in the setting of cutaneous abscess, including fever and malaise; toxicity is rare.
Cellulitis is pyogenic infection of the skin without an organized cavity and is typically limited to the epidermis, dermis, and superficial subcutaneous tissues ( Fig. 2 ). The hallmark physical findings of cellulitis include erythema, warmth, induration, and tenderness, although all criteria need not be present to make the diagnosis. In most cases, the margins of the infection are ill defined, although well-demarcated margins occur in group A streptococcal erysipelas. Cellulitis may present with fever and malaise, and severe toxicity is exceedingly uncommon. Clinical parameters of cellulitis overlap with skin abscess, because these infections lie within a spectrum; cases of cellulitis may evolve into abscess, and nearly all skin abscesses have some component of cellulitis immediately surrounding the abscess cavity. As a result of this overlap, SSTI diagnosis and treatment is challenging.
Microbiology
Most SSTIs result from infection with gram-positive cocci, specifically Staphylococcus aureus and group A streptococci. Although typical commensal organisms of the skin, bacteria infect the skin and soft tissues via direct inoculation, typical through disruption of the skin barrier. Proliferation of bacteria and development of cellulitis or abscess do not occur in a predictable fashion, and the clinical differentiation of superficial and dermal involvement versus presence of an abscess cavity may be difficult. Gram-negative organisms may also infect the skin and soft tissues, particularly in the buttock and axillary regions. Anaerobic bacteria are not typically present in cellulitis but are commonly implicated in necrotizing fasciitis as coinfecting organisms with S. aureus or group A streptococci.
Epidemiology and Emergence of CA-MRSA
In the United Sates, the incidence of SSTIs among the pediatric population has increased substantially in the previous 15 years. This upsurge is concomitant with emergence of community-associated strains of methicillin-resistant Staphylococcus aureus (CA-MRSA). Different from previous “hospital-acquired” or nosocomial strains (HA), CA-MRSA is a genetically distinct organism. The genes coding for methicillin resistance lie within the staphylococcal chromosomal cassette, or SCC mec gene, of which there are 4 predominant types. SCC mec type IV codes for CA-MRSA, and is a small, mobile genetic element, which facilitates transfer of methicillin resistance more readily than the larger elements coding for hospital-acquired methicillin-resistant Staphylococcus aureus (HA-MRSA). Clinical manifestations also differ, as CA-MRSA most commonly presents as skin infections, whereas HA-MRSA produces invasive infections, such as pneumonia and sepsis. It should be noted that the terms of “community” and “hospital” strains have become blurred, because CA-MRSA has been increasingly implicated in hospitalized and chronically ill populations.
Among SSTIs, cutaneous abscesses have had the most demonstrable increase in the era of CA-MRSA. Previously, skin abscesses were a result of methicillin-sensitive strains of S. aureus (MSSA); isolation of CA-MRSA from abscesses has since far surpassed that of MSSA. Because wound cultures are readily available after drainage, the microbiology of skin abscesses is well established, allowing for accurate epidemiologic surveillance. In the United States, the prevalence of CA-MRSA from cultured lesions is nearly universally greater than 50% and is as high as 70% to 80% in municipalities such as Chicago, Houston, and San Francisco.
Although great attention has been paid to CA-MRSA and SSTI in the United States, descriptions of CA-MRSA are occurring worldwide. The CA-MRSA strain ubiquitous across the United States were derived from the precursor strain USA300, although others are present around the world. Recent surveillance data have revealed that CA-MRSA is present on 6 continents and that prevalence in areas of Europe and South America rival that of the United States. In fact, analysis of CA-MRSA isolates across the Atlantic Ocean and Pacific Ocean have shown conservation of highly expressed virulence factors, such as Panton-Valentine leukocidin. Although CA-MRSA is present across the globe, similar dramatic increases in the incidence of SSTI as in the United States have yet to be documented.
Clinical and diagnostic approach
Clinical Evaluation
The usual approach to SSTI involves assessment of clinical findings, and at extremes of cellulitis and abscess, clinical assessment alone is useful in evaluation. Cellulitis involves the dermal and subcutaneous layers of skin, with erythema and signs of inflammation present: warmth, tenderness, and induration (hardness or firmness of the soft tissues). Most often, cellulitis develops after traumatic introduction of bacteria into the skin, from minor trauma (eg, scratching from fingernails, insect bites) or more significant penetrating injury. Rarely, cellulitis develops from direct extension local foci (eg, osteomyelitis) or from hematogenous seeding, with the latter more frequent in neonates. It is often helpful to demarcate the margins of the lesion using a pen or skin marker, as extent of the lesion is useful in determining progression of infection, response to therapy, and clinical resolution. Skin abscesses are clinically defined by findings similar to cellulitis, accompanied by fluctuance. Fluctuance often corresponds with the presence of a fluid-filled cavity. Skin abscesses frequently exist under pressure with surrounding inflammation, can cause pain, and may impair common activities in children depending on location; for example, buttock abscesses often preclude young children from sitting down. As pressure builds within the cavity, the infection may advance toward the skin and form a clear pustule, which may eventually “erupt” and produce spontaneous drainage of purulent material.
As previously mentioned, cellulitis and abscess exist as a spectrum of infections; therefore, there are many children present with SSTIs that are difficult to differentiate from a diagnostic perspective. In recent years, the advent of bedside ultrasound (US) has permitted enhanced diagnosis of SSTIs in the ED setting. Early studies in adults determined that US, in the hands of trained emergency medicine clinicians, was superior to physical examination in determining the presence of abscess. Furthermore, clinical management is positively affected, with improved accuracy of US documented in 48% of cases of suspected nondrainable lesions and 73% of suspected abscess. Increasingly, bedside US has been adopted by pediatric emergency physicians and exhibited similar promise in management in children with SSTI. Considering benefits, including low expense, rapidity of assessment, and diagnostic accuracy, bedside US will have an increasing role in ED management of pediatric SSTI.
Microbiologic Diagnosis
In the case of cutaneous abscess, pus is readily accessible for culture either spontaneously or following drainage, easily permitting isolation of the offending bacterium for clinical and surveillance purposes. Accordingly, the current bacteriology of skin abscess is well established, with the overwhelming majority cases resulting from S. aureus , either CA-MRSA or methicillin-sensitive Staphylococcus aureus (MSSA). Notably, there is little distinction between abscesses resulting from CA-MRSA or MSSA in terms of clinical presentation, risk factors, or abscess size; therefore, determination of the infecting organism is not possible without isolation in culture.
On the other hand, the bacteriology of cellulitis is not as well understood, in the absence of readily obtainable purulent material. The lack of microbiologic data for cellulitis has posed a dilemma for clinicians. Before the emergence of CA-MRSA, attempts to identify bacterial organisms have been made using needle aspiration, via insertion and aspiration of infected skin tissue either at the leading edge or point of maximal inflammation of the lesion. In addition, injection of a small amount of bacteriostatic saline (0.5 cc), followed by aspiration, has been postulated as a potential method. Unfortunately, yield of pathogens from these needle aspiration methods are highly variable, with infecting organisms identified anywhere from 10% to 60% of attempts.
Recently the approach to cellulitis has become even more confusing, as the prevalence of CA-MRSA among cellulitis is unknown. Nonetheless, emergency physicians are increasingly instituting CA-MRSA active therapy in cases of simple cellulitis. However, many experts maintain that group A streptococcus remains a primary cause of cellulitis and erysipelas; therefore emergency clinicians should maintain suspicion for these organisms. Recent data have supported this claim, at least in adults, with more than 70% of patients with cellulitis having serology consistent with group A streptococcal infection.
Surgical therapy
Once the presence of a skin abscess has been determined, the mainstay of therapy remains incision and drainage of the lesion. Removal of purulent material provides immediate relief from pain and improves healing. Incision and drainage procedures are frequently performed in the ED setting, in the hands of general and pediatric emergency physicians. Consultation with general surgery may be obtained in situations where the abscess is close to sensitive structures (eg, face, perineum, and genitalia) or in cases where an extremely deep, complex lesion is suspected. Performance of an incision and drainage procedure is discussed later in this article.
Sedation and Analgesia
Before drainage of cutaneous abscess, consideration should always be given regarding analgesia, because these infections produce substantial pain for children. Removal of purulent material reduces pain in children, although drainage procedures are often painful as well. Therefore, adjunctive sedation and analgesia is necessary when the procedure is completed in the ED. Literature specific to sedation and analgesia for abscess management is very limited, although the approach used for procedures such as laceration repair is often used. Topical anesthetic, specifically eutectic mixture of local anesthetics, has been used for superficial anesthesia and to promote drainage through maceration of thin skin or pustules at a site of eruption. Topical anesthesia is only adjunctive, however, as the maximal depth of action in healthy tissue is just 3 mm after 60 minutes of application.
Local anesthesia, with infiltrated lidocaine, is often used. Smaller lesions, which do not require extensive debridement, are often excellent candidates for local anesthesia alone. Larger lesions may be more challenging because injection directly into the abscess may not result in adequate anesthesia owing to the inflamed and necrotic tissue. Infiltration around the lesion into healthy tissue is an option; so-called “field block” can provide sufficient analgesia in older children and adolescents who can tolerate injection, allowing for incision, drainage, and debridement of the wound. Local anesthesia is often difficult to use for lesions in sensitive areas (eg, genitourinary) or in young children.
Procedural sedation is often instituted for ED abscess drainage in the pediatric population. The primary goal of procedural sedation in the context of skin abscesses is to permit adequate drainage; therefore, the level of sedation achieved should only be that necessary for completion of the procedure. Procedural sedation is often of greater utility for young children or for larger-sized lesions. Comprehensive review of the approach to sedation, including method of administration and choice of pharmacologic agents is beyond the scope of this article, although commonly selected approaches include oral, intranasal, or intravenous benzodiazepines, intravenous, ketamine, or propofol, or a combination approach.
Method of Incision and Drainage
Removal of purulent material from skin abscesses is best accomplished in an organized and stepwise fashion ( Table 1 ). Sterile preparation of the area, including antiseptic solution, sterile draping, and sterile gloves, is typically been recommended. Incision of the lesion at the area of maximal fluctuance is performed using a scalpel (usually a 11-blade), creating a linear opening across the length of the fluctuance ( Fig. 3 ). Larger incisions (>1–2 cm) with sufficient depth may be required to permit sufficient access to the abscess cavity. Expressed pus should be sent for wound culture, both for surveillance and treatment purposes. After manual expression of purulent material, probing and debridement of the abscess using a blunt instrument, ideally a hemostat, should be performed ( Fig. 4 ). Many abscesses are complex, with septations and loculations, and lysis of this tissue may release other collections of purulence. Therefore, aggressive debridement to the margins of the abscess cavity is indicated. Following debridement and repeat expression, forceful irrigation of the cavity with sterile saline may be performed. Management of the open abscess cavity remains controversial and is discussed later.
| Recommended Steps | Materials | Comment |
|---|---|---|
| Analgesia and sedation | Dependent on many variables, including lesion size, patient age, and clinician preference | |
| Sterile preparation | Povidone-iodine | |
| Incision | 11-blade scalpel | Incise ½–2/3 or fluctuance |
| Manual expression | ||
| Wound culture | Bacterial culturette | Recommended by CDC and IDSA |
| Lysis of intracavitary septae | Blunt or curved hemostat | Define margin of lesion to assure septations are disrupted |
| Manual expression | ||
| Saline irrigation (optional) | 20 cc syringe, 18–20 g angiocath, normal saline | No literature to support, although may be used to clear debris |
| Wound stent (optional) | Strip of iodoform gauze, vessel loop, section of penrose drain | Suggested for large lesions-packing not recommended |
Wound Management
Among the most controversial debates with respect to abscess management is the utility of wound packing. Complete packing of the abscess cavity with gauze strip (eg, iodoform) has customarily been used to aid in debridement, avoid reaccumulation, and permit healthy tissue growth with closure of the wound. After placement, packing is usually removed within 24 to 48 hours and then replaced if continued purulent or necrotic material is present. Difficulties in the use of wound packing in children, specifically pain incurred with placement, removal, and replacement (if necessary), has led to increasing literature discouraging this practice. Recent randomized clinical trials have found that healing rates are equivalent whether drained abscesses are packed or not packed, although packing was associated with increased pain and analgesic use. As a result, this practice is less frequently used in children, with nearly 50% or practitioners avoiding wound packing after drainage.
Alternatives to packing are occasionally used for large lesions. Wound “stents” are an option, involving insertion of a strip of iodoform or section of penrose drain secured into the open incision. The stent is maintained for several days to promote continued drainage of the abscess cavity by preventing premature closure of the incision. Although more commonly used, formal assessments of this method are lacking.
Recently, loop drains have been proposed as an alternative to wound packing. Loop drains involve drainage via the recommended method, including debridement and irrigation, followed by tunneling of the tract and passage of a rubber vessel loop between the incision and distal healthy tissue ( Fig. 5 ). The ends of the vessel loop are then tied together securely to form an annular wound stent. After approximately 3 days, the loop drain is cut and easily removed. Acceptable outcomes of abscesses treated in this manner have been described, and the literature appears promising. However, utility of loop drains have not undergone systematic evaluation.
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