Streptococcal Skin Infections

Group A
-hemolytic streptococci are not normal skin flora. Streptococcal skin infections result from colonization of normal skin by contact with other infected individuals or by preceding streptococcal respiratory infection.
Clinical Findings
SYMPTOMS AND SIGNS
Impetigo is a focal, vesicular, pustular lesion with a thick, amber-colored crust with a "stuck-on" appearance.
Erysipelas is a painful superficial cellulitis that frequently involves the face. It is well demarcated from the surrounding normal skin. It affects skin with impaired lymphatic drainage, such as edematous lower extremities or wounds.
LABORATORY FINDINGS
Cultures obtained from a wound or pustule are likely to grow group A streptococci. Blood cultures are occasionally positive.
Treatment
Parenteral antibiotics are indicated for patients with facial erysipelas or evidence of systemic infection. Penicillin, 2 million units intravenously every 4 hours, is the drug of choice. However, staphylococci infections may at times be difficult to differentiate from streptococcal infections. In practice, initial therapy for patients with risk factors for Staphylococcus aureus (eg, injection drug use, diabetes, wound infection) should cover this organism. Nafcillin, 1.5 g every 6 hours intravenously, and cefazolin, 1 g intravenously or intramuscularly every 8 hours, are reasonable choices. In the patient with a serious penicillin allergy (ie, anaphylaxis), vancomycin, 1000 mg intravenously every 12 hours, should be used.
Patients who do not require parenteral therapy may be treated with amoxicillin, 750 mg twice daily for 7–10 days. A first-generation oral cephalosporin, eg, cephalexin, 500 mg four times daily, or clindamycin, 300 mg orally three times daily, is an alternative to amoxicillin.

Other Group A Streptococcal Infections
Arthritis, pneumonia, empyema, endocarditis, and necrotizing fasciitis are relatively uncommon infections that may be caused by group A streptococci. Toxic shock-like syndrome also occurs.
Arthritis generally occurs in association with cellulitis. In addition to intravenous therapy with penicillin G, 2 million units every 4 hours (or cefazolin or vancomycin in doses recommended above for penicillin-allergic patients), frequent percutaneous needle aspiration should be performed to remove joint effusions. Open surgical drainage may be necessary when the hip or shoulder is infected.
Pneumonia and empyema often are characterized by extensive tissue destruction and an aggressive, rapidly progressive clinical course associated with significant morbidity and mortality. High-dose penicillin and chest tube drainage are indicated for treatment of empyema. Vancomycin is an acceptable substitute in penicillin-allergic patients.
Group A streptococci can cause endocarditis. Endocarditis should be treated with 4 million units of penicillin G intravenously every 4 hours for 4–6 weeks. Vancomycin, 1 g intravenously every 12 hours, is recommended for persons allergic to penicillin.
Necrotizing fasciitis is a rapidly spreading infection involving the fascia of deep muscle. The clinical findings at presentation may be those of severe cellulitis, but the presence of systemic toxicity and severe pain, which may be followed by anesthesia of the involved area due to destruction of nerves as infection advances through the fascial planes, is a clue to the diagnosis. Surgical exploration is mandatory when the diagnosis is suspected. Early and extensive debridement is essential for survival.
Any streptococcal infection—and necrotizing fasciitis in particular—can be associated with streptococcal toxic shock syndrome, typified by invasion of skin or soft tissues, acute respiratory distress syndrome, and renal failure. The very young, the elderly, and those with underlying medical conditions are at particularly high risk for invasive disease. Bacteremia occurs in most cases. Skin rash and desquamation may not be present. Mortality rates can be up to 80%. The syndrome is due to elaboration of pyrogenic erythrotoxin (which also causes scarlet fever), a superantigen that stimulates massive release of inflammatory cytokines believed to mediate the shock. A
-lactam remains the drug of choice for treatment of serious streptococcal infections, but clindamycin, which is a potent inhibitor of toxin production, should also be administered at a dose of 600 mg every 8 hours intravenously for invasive disease, especially in the presence of shock. Intravenous immune globulin has also been recommended for streptococcal toxic shock syndrome for presumed, although unproven, therapeutic benefit from specific antibody to streptococcal exotoxins in immune globulin preparations. Two dosage regimens have been used: 450 mg/kg once daily for 5 days or a single dose of 2 g/kg with a repeat dose at 48 hours if the patient remains unstable.
Outbreaks of invasive disease have been associated with colonization by invasive clones that can be transmitted to close contacts who, though asymptomatic, may be a reservoir for disease. Tracing contacts of patients with invasive disease is controversial.

Stevens DL et al; Infectious Diseases Society of America. Practice guidelines for the diagnosis and management of skin and soft-tissue infections. Clin Infect Dis. 2005 Nov 15;41(10): 1373–406. [PMID: 16231249]

Vinh DC et al. Rapidly progressive soft tissue infections. Lancet Infect Dis. 2005 Aug;5(8):501–13. [PMID: 16048719]

Non-Group A Streptococcal Infections
Non-group A hemolytic streptococci (eg, groups B, C, and G) produce a spectrum of disease similar to that of group A streptococci. The treatment of infections caused by these strains is the same as for group A streptococci.
Group B streptococci are an important cause of sepsis, bacteremia, and meningitis in the neonate. Antepartum screening to identify carriers and peripartum antimicrobial prophylaxis are recommended in pregnancy. This organism, part of the normal vaginal flora, may cause septic abortion, endometritis, or peripartum infections and, less commonly, cellulitis, bacteremia, and endocarditis in adults. Treatment of infections caused by group B streptococci is with either penicillin or vancomycin in doses recommended for group A streptococci. Because of in vitro synergism, some experts recommend the addition of low-dose gentamicin, 1 mg/kg every 8 hours.
Viridans streptococci, which are nonhemolytic or
-hemolytic (ie, producing a green zone of hemolysis on blood agar), are part of the normal oral flora. Although these strains may produce focal pyogenic infection, they are most notable as the leading cause of native valve endocarditis (see below).
Group D streptococci include Streptococcus bovis and the enterococci. S bovis is a cause of endocarditis in association with bowel neoplasia or cirrhosis and is treated like viridans streptococci.

Edwards MS et al. Group B streptococcal infections in elderly adults. Clin Infect Dis. 2005 Sep 15;41(6):839–47. [PMID: 16107984]