Strategies for Diagnosis and Treatment of Impetigo

April 3, 2007 — Diagnosis and treatment strategies for impetigo are reviewed in the March 15 issue of American Family Physician.

"Impetigo is a highly contagious infection of the superficial epidermis that most often affects children two to five years of age, although it can occur in any age group," write Charles Cole, MD, and John Gazewood, MD, MSPH, from the University of Virginia School of Medicine in Charlottesville. "Among children, impetigo is the most common bacterial skin infection and the third most common skin disease overall, behind dermatitis and viral warts. Impetigo is more common in children receiving dialysis."

The authors searched Ovid Evidence-Based Medicine, the National Guideline Clearinghouse, the TRIP database, Clinical Evidence, and MEDLINE (1996 - 2005) and reviewed appropriate articles about impetigo.
There are 2 types of impetigo: nonbullous impetigo (impetigo contagiosa) and bullous impetigo. The former represents a host response to the infection, whereas the latter is caused by staphylococcal toxin, and no host response is required to manifest clinical illness.

Staphylococcus aureus is the most important causative organism; Streptococcus pyogenes (group A β-hemolytic streptococcus) causes fewer cases, either alone or combined with S aureus.

The diagnosis of impetigo usually is made clinically, but confirmation with Gram stain and culture may be helpful on occasion. Culture may help identify patients with nephritogenic strains of S pyogenes during outbreaks of poststreptococcal glomerulonephritis, or methicillin-resistant S aureus in suspected cases.

Nonbullous impetigo starts as a single red macule or papule that rapidly becomes a vesicle that ruptures easily to form an erosion. The vesicle contents dry to form characteristic honey-colored, often pruritic crusts. Autoinoculation often causes spread to surrounding areas. Nonbullous impetigo often affects the extremities, face, or other areas subject to trauma. If the infection is not treated, it usually resolves spontaneously without scarring in several weeks.

Impetiginous or secondary impetigo is a subtype of nonbullous impetigo that can complicate systemic diseases, such as diabetes mellitus and AIDS.
Bullous impetigo occurs most frequently in neonates but also can occur in older children and adults. This form of impetigo is a localized form of staphylococcal scalded skin syndrome caused by toxin-producing S aureus. Superficial vesicles rapidly develop into enlarging, flaccid bullae with sharp margins and no surrounding erythema. Yellow crusts with oozing occur when the bullae rupture. The "collarette" of scale surrounding the blister roof at the periphery of ruptured lesions is pathognomonic.

This form of impetigo typically develops at moist, intertriginous areas, such as the diaper area, axillae, and neck folds. Systemic symptoms are infrequent but can include weakness, fever, and diarrhea. Cases are usually sporadic and self limited, resolving in a few weeks without scarring.

Impetigo usually heals spontaneously within 2 weeks without scarring. However, treatment helps alleviate discomfort, improves cosmetic appearance, and prevents the spread of an organism linked to other illnesses, such as glomerulonephritis. In 5 placebo-controlled randomized trials, 7-day cure rates ranged from 0% to 42%.

Adults may have a higher risk for complications than children. Incidence of acute poststreptococcal glomerulonephritis is between 1% and 5% of patients with nonbullous impetigo, and the risk for this serious complication is not affected by treatment with antibiotics. Other rare potential complications include sepsis, osteomyelitis, arthritis, endocarditis, pneumonia, cellulitis, lymphangitis or lymphadenitis, guttate psoriasis, toxic shock syndrome, and staphylococcal scalded skin syndrome.
Despite the lack of standard treatment of impetigo, many options are available. The topical antibiotics mupirocin and fusidic acid are effective and may be superior to oral antibiotics, but the latter should be considered for patients with extensive disease. Topical disinfectants are not helpful to treat impetigo.

Although oral penicillin V is seldom effective, there is otherwise no clear preference among antistaphylococcal penicillins, amoxicillin/clavulanate, cephalosporins, and macrolides. However, resistance rates to erythromycin are rising.
Specific recommendations are as follows:
• For impetigo involving limited body surface area, topical antibiotics such as mupirocin and fusidic acid (not available in the United States) are the preferred first-line therapy (level of evidence, A).

• Oral antibiotics that are effective for treatment of impetigo are antistaphylococcal penicillins, amoxicillin/clavulanate, cephalosporins, and macrolides. Erythromycin is less effective (level of evidence, A).

• For patients with more extensive impetigo or disease associated with systemic symptoms, oral antibiotics should be considered (level of evidence, C).

• Oral penicillin V, amoxicillin, topical bacitracin, and neomycin are not recommended for the treatment of impetigo (level of evidence, B).

• Topical disinfectants such as hydrogen peroxide should not be used in the treatment of impetigo (level of evidence, B).

"Treatments ideally should be effective, inexpensive, and have limited side effects," the authors conclude. "Topical antibiotics have the advantage of being applied only where needed, which minimizes systemic side effects. However, some topical antibiotics may cause skin sensitization in susceptible persons."

Clinical Context
Impetigo, a highly contagious infection of the superficial epidermis, typically affects children aged 2 to 5 years, but it can affect people of all ages. It is the most common bacterial skin infection in children and the third most common skin disease overall. Nonbullous impetigo (impetigo contagiosa) represents a host response to the infection, whereas bullous impetigo is caused by staphylococcal toxin. S aureus is the most important causative organism; S pyogenes (group A β-hemolytic streptococcus) is responsible for fewer cases.

Impetigo is usually diagnosed clinically and can be confirmed by Gram stain and culture, but this is seldom necessary. Although impetigo usually heals spontaneously within 2 weeks without scarring, treatment helps to relieve discomfort, improve cosmetic appearance, and prevent the spread of staphylococcal infections. Despite the lack of standard treatment of impetigo, many options are available and effective.

Study Highlights
• The reviewers searched Ovid Evidence-Based Medicine, the National Guideline Clearinghouse, the TRIP database, Clinical Evidence, and MEDLINE (1996 - 2005) for articles about impetigo.

• Impetigo is usually transmitted through direct contact and often spreads rapidly through schools and daycare centers. After excoriating an infected area, patients can further spread the infection to themselves or others, and fomites also are important in the spread of impetigo. The incidence is greatest in the summer months, especially in crowded living conditions or in areas with poor hygiene.

• In 1 UK study, annual incidence of impetigo was 2.8% in children 4 years or younger and 1.6% among children 5 to 15 years of age.

• Impetigo is usually diagnosed clinically and is occasionally confirmed with Gram stain and culture, which can help identify patients with nephritogenic strains of S pyogenes or methicillin-resistant S aureus.

• In nonbullous impetigo, a red macule or papule on the extremities, face, or other areas subject to trauma rapidly becomes a vesicle that ruptures to form an erosion. The vesicle contents dry to form characteristic honey-colored, often pruritic crusts.

• Impetiginous (secondary) impetigo is a type of nonbullous impetigo associated with systemic diseases, such as diabetes mellitus and AIDS. Insect bites, varicella, herpes simplex virus, and other conditions disrupting skin integrity predispose patients to common impetigo.

• In bullous impetigo, superficial vesicles at moist, intertriginous areas rapidly develop into enlarging, flaccid bullae with sharp margins and no surrounding erythema. Yellow crusts with oozing occur when the bullae rupture. The "collarette" of scale surrounding the blister roof at the periphery of ruptured lesions is pathognomonic. This form of impetigo, which is seen most often in neonates but also can occur in older children and adults, is a localized form of staphylococcal scalded skin syndrome caused by toxin-producing S aureus.

• For impetigo involving limited body surface area, topical antibiotics such as mupirocin and fusidic acid (not available in the United States) are effective and are the preferred first-line therapy. Topical antibiotics are applied only where needed, thereby minimizing systemic adverse effects, but they may cause skin sensitization in susceptible persons.

• Topical disinfectants are not helpful to treat impetigo, and topical bacitracin and neomycin are not recommended.

• For patients with more extensive impetigo or disease associated with systemic symptoms, oral antibiotics should be considered. Although oral penicillin V or amoxicillin are seldom effective, there is otherwise no clear preference among antistaphylococcal penicillins, amoxicillin/clavulanate, cephalosporins, and macrolides. However, resistance rates to erythromycin are rising, thus making it less effective.

• Without treatment, most cases of impetigo resolve spontaneously in 2 weeks without treatment. In 5 placebo-controlled randomized trials, 7-day cure rates ranged from 0% to 42%.

• Adults may have a higher risk for complications than children. Incidence of acute poststreptococcal glomerulonephritis is between 1% and 5% of patients with nonbullous impetigo, and the risk for this serious complication is not affected by treatment with antibiotics. Other rare potential complications include sepsis, osteomyelitis, arthritis, endocarditis, pneumonia, cellulitis, lymphangitis or lymphadenitis, guttate psoriasis, toxic shock syndrome, and staphylococcal scalded skin syndrome.