Superficial folliculitis | Infection of hair follicles of the skin | Poor hygiene, occupational exposure to oils and solvents | Staphylococcus aureus most common | Single or multiple superficial, dome-shaped, pruritic pustules at the ostium of hair follicles on the scalp, back, and/or extremities | Diagnosis usually made clinically; Gram stain and bacterial cultures support the clinical diagnosis |
Hot tub folliculitis | Infection of hair follicles of the skin | Whirlpools and hot tubs with low chlorine, high pH, and high water temperatures | Pseudomonas aeruginosa | Small erythematous pruritic papules topped by pustules in areas submerged in hot water | Clinical diagnosis supported by bacterial culture and Gram stain of infected pustule or water source |
Furuncle | Acute bacterial infection of perifollicular skin, usually from preexisting folliculitis | Skin areas subject to friction and perspiration, poor hygiene, occupational exposure to grease or oil, malnutrition, alcoholism, and immunosuppression | S. aureus | Indurated, dull red, tender nodule with central purulent core on the face, buttocks, perineum, breast, and/or axilla | Diagnosis usually made clinically; Gram stain and culture of suppurative lesion support the clinical diagnosis |
Carbuncle | Coalescence of interconnected furuncles; involves subcutaneous tissue with drainage at multiple sites | For untreated furuncles, complications include bacteremia, endocarditis, and osteomyelitis | S. aureus | Multiple abscess formations separating connective tissue septae with drainage to surface along hair follicles | Diagnosis usually made clinically; Gram stain and culture of suppurative lesion support the clinical diagnosis |
Paronychia | Infection of the nail folds | Minor trauma causing break in the skin, as produced by splinters Chronic: frequent immersion of hands in water | Acute: staphylococci, beta-hemolytic streptococci, gram-negative enteric bacteria Chronic: Candida albicans | Tender, red, swollen areas extending around the nail fold with or without pus | Clinical diagnosis supported by bacterial and/or fungal cultures of infected areas |
Impetigo contagiosa (nonbullous) | Localized purulent infection of the skin | Children (2-5 years old) living in warm, humid climates; poor hygiene; preexisting superficial abrasions from insect bites, trauma, and other causes | Group A beta-hemolytic streptococci and S. aureus | Small superficial vesicles that form pustules rupture, forming characteristic yellow-brown, “honey-colored” crusted lesions | Clinical diagnosis supported by culture/Gram stain of base of early lesion positive for staphylococci and/or streptococci; anti-DNase B and antihyaluronidase titers may be elevated |
Bullous impetigo | Localized purulent infection of the skin causing bullous lesions | Occurs in newborns and younger children on nontraumatized skin of the buttocks, perineum, trunk, and/or face | Usually due to S. aureus producing exfoliative toxins | Begins as small vesicles that quickly enlarge to form bullae with clear fluid that rupture and leave a brownish black crust | Clinical diagnosis supported by culture/Gram stain of base of lesion or clear fluid from bullae showing staphylococci |
Staphylococcal scalded skin syndrome (SSSS) | Widespread bullae and exfoliation as a severe manifestation of an infection by S. aureus strains producing exfoliative exotoxins | Higher incidence in newborns and younger children | S. aureus producing exfoliative exotoxins | Scarlatiniform rash with widespread tender bullae with clear fluid; bullae rupture, resulting in separation of skin; exfoliation exposes large areas of red skin | Diagnosis usually made clinically |
Ecthyma | A variant of impetigo on the lower extremities causing punched-out ulcerative lesions | May occur de novo or secondary to preexisting superficial abrasions such as insect bites; occurs in children and elderly most often | Usually group A beta-hemolytic streptococci | “Punched-out” ulcers with yellow crust extending into dermis, typically on lower extremities | Clinical diagnosis supported by culture and Gram stain of base of lesion that is positive for streptococci |
Erythrasma | Superficial chronic bacterial infection of the skin | More common in males, obese patients, and patients with diabetes mellitus | Corynebacterium minutissimum | Slowly spreading pruritic, red brown macules with scales—affecting axillae, groin, and toes | Gram-stained imprints of skin lesions reveal gram-positive bacilli; examination of skin under Wood's lamp reveals distinctive red coral fluorescence |
Erysipelas | Acute inflammation of superficial layers of the skin with lymphatic involvement | Occurs most often in infants, young children, and elderly; those with skin ulcers, local trauma/abrasion, and eczematous lesions; increased susceptibility in sites with impaired lymphatic drainage | Group A beta-hemolytic streptococci; rarely, group B, C, G streptococci and S. aureus | 5%-20% facial, 70%-80% lower extremity; painful, bright red, edematous, indurated lesions with raised border, well demarcated from uninvolved skin; regional lymphadenopathy common | Difficult to culture group A streptococci from lesion; up to 20% of throat cultures positive for group A streptococci; blood culture positive in 5% of cases |
Cellulitis | Diffuse suppurative inflammation of skin and subcutaneous tissues | Occurs in sites of previous tissue damage such as operative wounds, ulcers, and focal trauma; increased incidence in intravenous drug abusers | Nonimmunosuppressed hosts: commonly group A beta-hemolytic streptococci; less commonly S. aureus; group B and G streptococci in patients with lower extremity edema; gram-negative rods in immunosuppressed patients; Pasteurella in cat and dog bites | Localized, painful, erythematous, warm lesions, poorly demarcated from uninvolved skin; regional lymphadenopathy may be present; bacteremia and gangrene may occur if untreated | Gram stain/culture of purulent exudate from advancing edge may reveal etiologic agent; blood cultures positive in 25% of cases |
Synergistic necrotizing cellulitis (nonclostridial anaerobic cellulitis) | A variant of necrotizing fasciitis (see following entities) involving skin, muscle, subcutaneous tissue, and fascia | Diabetes mellitus, obesity, advancing age, cardiac, and renal disease | Mixture of anaerobes (anaerobic streptococci and Bacteroides most commonly) and facultative bacteria (Klebsiella, E. coli, Proteus) | Acute onset of tender skin ulcers in lower extremity draining foul-smelling, red-brown (“dishwater”) pus, with underlying gangrene of subcutaneous tissue and muscle; tissue gas in 25% of patients; systemic toxicity is significant | Culture/Gram stain of exudate aspirated from lesion |
Necrotizing fasciitis (Type I) | A deep-seated, severe necrotizing infection of the subcutaneous tissue, resulting in progressive destruction of superficial and, in some cases, deep fascia and fat | Diabetes mellitus, alcoholism, parenteral drug abuse; occurs at sites of trauma such as an insect bite, and following laparotomy performed in the presence of perineal soiling, decubitus ulcers, and perirectal abscesses | At least 1 anaerobic species (most commonly Bacteroides or Peptostreptococcus) along with a facultative anaerobic species such as streptococci or gram-negative enteric bacilli such as E. coli, Enterobacter, Klebsiella, and Proteus | Sudden onset of tender, warm, erythematous, well-demarcated cellulitis, usually involving the lower extremity, abdominal wall, perianal, and/or groin areas; sequential skin color changes from red-purple to patchy blue-gray over several days; within 3-5 days, skin breakdown occurs with bullae, a seropurulent exudate, frank cutaneous gangrene, and skin anesthesia; high fevers and systemic toxicity with early shock and organ failure common | Surgical exploration required to distinguish from cellulitis; leukocytosis, thrombocytopenia, azotemia, and increased serum levels of creatine kinase (CK) may be present; Gram-stained smears of exudates reveal a mixture of organisms; blood cultures are frequently positive; subcutaneous gas and soft tissue swelling detectable on radiographs |
Necrotizing fasciitis (Type II) (also known as hemolytic streptococcal gangrene) | A deep-seated, severe, necrotizing infection of the subcutaneous tissue, resulting in progressive destruction of superficial and, in some cases, deep fascia and fat | Occurs in 50% of patients with streptococcal toxic shock syndrome; predisposing factors also include diabetes mellitus, long-term steroid therapy, cirrhosis, peripheral vascular disease, a recent history of minor trauma, stab wounds, and surgical procedures | Group A streptococci, either alone or in combination with other species, most commonly S. aureus | Sudden onset of tender, warm, erythematous, well-demarcated cellulitis, usually involving the lower extremity, abdominal wall, perianal, and groin areas; sequential skin color changes from red-purple to patchy blue-gray over several days; within 3-5 days, bullae develop with seropurulent exudate, frank cutaneous gangrene, and skin anesthesia; high fevers and systemic toxicity with early shock and organ failure | Surgical exploration required to distinguish from cellulitis; leukocytosis, thrombocytopenia, azotemia, and increased serum levels of CK may be present; Gram-stained smears of exudate reveal gram-positive cocci in chains; surgical debridement provides tissue for culture and Gram stain; subcutaneous gas and soft tissue swelling present on radiograph |
Clostridial anaerobic cellulitis | A necrotizing clostridial infection of devitalized subcutaneous tissue with rare involvement of deep fascia or muscle | Dirty or inadequately debrided traumatic wounds; preexisting localized infection; contamination of surgical wounds | Clostridial species, usually Clostridium perfringens | Localized edema of wound site; thin, foul-smelling drainage of wound with minimal pain, extensive gas formation in tissues, and frank crepitant cellulites | Gram stain of drainage shows numerous blunt-ended, thick, gram-positive bacilli and variable numbers of neutrophils; soft tissue radiographic films show abundant gas |
Clostridial myonecrosis (gas gangrene) | Rapidly progressive infection characterized by muscle necrosis and systemic toxicity caused by potent clostridial exotoxins | Wounds associated with trauma and open fractures such as gunshot wounds; intestinal and biliary tract surgery | C. perfringens accounts for 80% of cases; other species include C. septicum, C. novyi, and C. sordelli; the toxins released by these organisms are responsible for much of the morbidity and mortality associated with these infections | Sudden onset of severe pain at the site of a wound with rapid progression to localized tense edema and pallor; crepitance is a late finding and is neither a sensitive nor a specific feature; as the lesion progresses, the skin progresses to magenta or brown discoloration with brown serosanguinous discharge and “mousey” odor | Surgical exploration critical in demonstrating devitalized muscle tissue; CT scan shows gas in the muscle and in fascial planes with soft tissue swelling; Gram stain of exudate shows typical gram-positive or gram-variable rods with spores and lysed or absent neutrophils; with C. perfringens, organism shows typical boxcar appearance without spores on Gram stain, “double-zone hemolysis” on anaerobic blood plate, and lecithinase activity (alpha-toxin); elevated CK, LDH, and myoglobin due to myonecrosis |
Spontaneous or nontraumatic gas gangrene | Rapidly progressive infection characterized by muscle necrosis and systemic toxicity caused by clostridial infection | Hematologic malignancies, colon cancer, diabetes mellitus, peripheral vascular disease; commonly with no obvious portal of entry; not associated with traumatic or surgical wounds | Most cases due to C. septicum | Sudden onset of pain and localized swelling of extremity, followed by discoloration, blister formation, and crepitance; associated fever, abdominal pain, vomiting, and diarrhea | Surgical exploration critical in demonstrating myonecrosis; CT scan shows gas in the muscle and fascial planes with soft tissue swelling; Gram stain of exudate shows typical gram-positive or gram-variable rods with spores and lysed or absent neutrophils; elevated CK, LDH, and myoglobin due to myonecrosis |