Impetigo

Background

Impetigo is an infectious bacterial infection of the skin caused by either Staphylococcus aureus, Streptococcus pyogenes (Group A streptococcus), or both. This infection may present with small vesicles which may progress to flaccid bullae. With time, the lesions develop a characteristic honey-colored crust and heal without scarring. The lesions most commonly occur on the face or extremities.

AGE RANGE-MEDIAN All ages
Most common in infants and children with nonbullous form

EPIDEMIOLOGIC ASSOCIATIONS CHARACTERIZATION

Transmission-Nonbullous
Contagious
Usually on previously damaged skin (insect bites, trauma)

Staph impetigo cases have pathogens occurring in the nose before cutaneous disease appears
Nasal carriage is as high as 20-50% in the general population

10-30% are never colonized
40-70% intermittent nasal carriers
10-30% persistent carriers

In streptococcal cases, S. pyogenes colonizes the skin and can be transferred from one lesion to another and from one mucous membrane surface to another

Organisms can survive an average of 10 days on the skin before the lesions appear
Colonization of the mucous membranes of the now or throat occur about 2-3 weeks after S. pyogenes appears on the skin

NOTE: Strains of S. pyogenes associated with impetigo nearly always differ from pharyngitis strains.

Bullous Less contagious than nonbullous form
Usually sporadic disorder

DISEASE ASSOCIATIONS CHARACTERIZATION

Acute poststreptococcal glomerulonephritis
Complication of streptococcal pyoderma

PATHOGENESIS CHARACTERIZATION

Bullous type Caused by phage group II-induced epidermolytic toxin of Staphylococcus aureus , causing cleavage within the epidermis

Non-bullous type Staphylococcus aureus agent in 80% of cases
Streptococcus in 10%
Mixture in 10%

GROSS APPEARANCE/CLINICAL VARIANTS CHARACTERIZATION

General

Nonbullous
Hot moist climates
Red macules or papules evolving into vesicles on erythematous base
Transform into pustules and rupture within a day
Treatment or spontaneous resolution usually within 2 weeks

Bullous
Newborns and infants frequently but any age can be affected
Extremities, trunk, and face
Superficial vesicles rapidly enlarge to flaccid bullae with sharp margins and no surrounding erythema
Bullae commonly rupture

VARIANTS

Impetiginized skin Inflammed skin, especially in atopic dermatitis, frequently harbors S. aureus with a higher density of organisms in exudative lesions

HISTOLOGICAL TYPES CHARACTERIZATION

General

Non-bullous
Neutrophils within the stratum corneum and epidermis
Sparse acantholytic cells
Perivascular inflammatory infiltrate in the dermis

Bullous
Subcorneal bullae with neutrophils and acantholysis

SPECIAL STAINS/IMMUNOPEROXIDASE/OTHER CHARACTERIZATION

Special stains Gram stain may detect bacteria unless the lesion is secondary to phage-induced toxin

PROGNOSIS AND TREATMENT CHARACTERIZATION

Treatment Topical antibiotics good if only few lesions, not as effective in bullous forms
Systemic antibiotics advisable in acute postreptococcal glomerulonephritis, usually given for 5-7 days

Erythromycin
Dicloxacillin
Clindamycin
Cephalexin

Impetiginized skin

May be little clinical benefit to treating severe atopic eczema with topical or systemic antibiotics which may encourage antimicrobial resistance

If there are no signs of infection, patients with atopic eczema should not receive antibiotics for cutaneous disease

FUSIDIC ACID

Fusidic acid cream in the treatment of impetigo in general practice: double blind randomised placebo controlled trial.

Koning S, van Suijlekom-Smit LW, Nouwen JL, Verduin CM, Bernsen RM, Oranje AP, Thomas S, van der Wouden JC.

Department of General Practice, University Hospital Rotterdam, Room Ff325, PO Box 1738, Erasmus University, 3000 DR Rotterdam, Netherlands.
BMJ 2002 Jan 26;324(7331):203-6 Abstract quote
OBJECTIVE: To test the hypothesis that fusidic acid would not increase the treatment effect of disinfecting with povidone-iodine alone in children with impetigo.

DESIGN: Randomised placebo controlled trial.

SETTING: General practices in Greater Rotterdam.

PARTICIPANTS: 184 children aged 0-12 years with impetigo.

MAIN OUTCOME MEASURES: Clinical cure and bacterial cure after one week.

RESULTS: After one week of treatment 55% of the patients in the fusidic acid group were clinically cured compared with 13% in the placebo group (odds ratio 12.6, 95% confidence interval 5.0 to 31.5, number needed to treat 2.3). After two weeks and four weeks the differences in cure rates between the two groups had become smaller. More children in the placebo group were non-compliant (12 v 5) and received extra antibiotic treatment (11 v 3), and more children in the placebo group reported adverse effects (19 v 7). Staphylococcus aureus was found in 96% of the positive cultures; no strains were resistant to fusidic acid.

CONCLUSIONS: Fusidic acid is much more effective than placebo (when both are given in combination with povidone-iodine shampoo) in the treatment of impetigo. Because of the low rate of cure and high rate of adverse events in the placebo group, the value of povidone-iodine in impetigo can be questioned.

N Engl J Med 1970;282:23-31
J Am Acad Dermatol 1987;17:62-63
N Engl J Med 1996;334:240-245.
Pediatr Dermatol 1987;4:2851-2862.
Int J Dermatol 1987;26:24-26.

Commonly Used Terms

Infectious and Microbiology

Skin

Internet Links

Last Updated 3/25/2002

DISEASE ASSOCIATIONS	CHARACTERIZATION
Acute poststreptococcal glomerulonephritis	Complication of streptococcal pyoderma

PATHOGENESIS	CHARACTERIZATION
Bullous type	Caused by phage group II-induced epidermolytic toxin of Staphylococcus aureus , causing cleavage within the epidermis
Non-bullous type	Staphylococcus aureus agent in 80% of cases Streptococcus in 10% Mixture in 10%

GROSS APPEARANCE/CLINICAL VARIANTS	CHARACTERIZATION
General
Nonbullous	Hot moist climates Red macules or papules evolving into vesicles on erythematous base Transform into pustules and rupture within a day Treatment or spontaneous resolution usually within 2 weeks
Bullous	Newborns and infants frequently but any age can be affected Extremities, trunk, and face Superficial vesicles rapidly enlarge to flaccid bullae with sharp margins and no surrounding erythema Bullae commonly rupture
VARIANTS
Impetiginized skin	Inflammed skin, especially in atopic dermatitis, frequently harbors S. aureus with a higher density of organisms in exudative lesions

HISTOLOGICAL TYPES	CHARACTERIZATION
General
Non-bullous	Neutrophils within the stratum corneum and epidermis Sparse acantholytic cells Perivascular inflammatory infiltrate in the dermis
Bullous	Subcorneal bullae with neutrophils and acantholysis

SPECIAL STAINS/IMMUNOPEROXIDASE/OTHER	CHARACTERIZATION
Special stains	Gram stain may detect bacteria unless the lesion is secondary to phage-induced toxin

PROGNOSIS AND TREATMENT	CHARACTERIZATION
Treatment	Topical antibiotics good if only few lesions, not as effective in bullous forms Systemic antibiotics advisable in acute postreptococcal glomerulonephritis, usually given for 5-7 days Erythromycin Dicloxacillin Clindamycin Cephalexin
Impetiginized skin	May be little clinical benefit to treating severe atopic eczema with topical or systemic antibiotics which may encourage antimicrobial resistance If there are no signs of infection, patients with atopic eczema should not receive antibiotics for cutaneous disease
FUSIDIC ACID
Fusidic acid cream in the treatment of impetigo in general practice: double blind randomised placebo controlled trial. Koning S, van Suijlekom-Smit LW, Nouwen JL, Verduin CM, Bernsen RM, Oranje AP, Thomas S, van der Wouden JC. Department of General Practice, University Hospital Rotterdam, Room Ff325, PO Box 1738, Erasmus University, 3000 DR Rotterdam, Netherlands.	BMJ 2002 Jan 26;324(7331):203-6 Abstract quote OBJECTIVE: To test the hypothesis that fusidic acid would not increase the treatment effect of disinfecting with povidone-iodine alone in children with impetigo. DESIGN: Randomised placebo controlled trial. SETTING: General practices in Greater Rotterdam. PARTICIPANTS: 184 children aged 0-12 years with impetigo. MAIN OUTCOME MEASURES: Clinical cure and bacterial cure after one week. RESULTS: After one week of treatment 55% of the patients in the fusidic acid group were clinically cured compared with 13% in the placebo group (odds ratio 12.6, 95% confidence interval 5.0 to 31.5, number needed to treat 2.3). After two weeks and four weeks the differences in cure rates between the two groups had become smaller. More children in the placebo group were non-compliant (12 v 5) and received extra antibiotic treatment (11 v 3), and more children in the placebo group reported adverse effects (19 v 7). Staphylococcus aureus was found in 96% of the positive cultures; no strains were resistant to fusidic acid. CONCLUSIONS: Fusidic acid is much more effective than placebo (when both are given in combination with povidone-iodine shampoo) in the treatment of impetigo. Because of the low rate of cure and high rate of adverse events in the placebo group, the value of povidone-iodine in impetigo can be questioned.