Impetigo
Key Points
Impetigo is a highly contagious bacterial skin infection
It is most common in warm tropical climates, with crowded living conditions, poor hygiene, and lower socioeconomic conditions
Impetigo is caused by Staphylococcus aureus or group A beta-hemolytic Streptococcus pyogenes, or both
There are two common forms of impetigo, nonbullous (70%) and bullous (30%) with distinct causes and clinical appearances
Nonbullous impetigo is caused by S. aureus or S. pyogenes and is characterized by superficial honey-colored crusted lesions on the face and extremities in areas of compromised skin
Bullous impetigo is caused by S. aureus and presents as large bullae located in intertriginous areas of the body that rupture and ooze yellow fluid
Impetigo is usually a self-limiting infection and usually resolves within 3 weeks
Antibiotic treatment is usually initiated for faster resolution and to prevent the spread to other individuals
The prognosis is excellent, but a small percentage of cases can progress to renal failure, septic arthritis, scarlet fever, and sepsis
Impetigo is a highly contagious bacterial skin infection of the superficial layers of the epidermis most commonly caused by gram-positive bacteria.1,2 Major risk factors include warm tropical climates, crowded living conditions, poor hygiene, lower socioeconomic conditions, daycare centers, crowded schools, close-contact sports, and poor immunity status.1,3,4,5,6,7 Impetigo is less frequently seen in northern climates during the summer months.8 It is seen most often in children, where it accounts for approximately 10% of skin disorders in pediatric patients.2
Normal skin is inhabited by large numbers of bacteria that usually do not lead to medical problems, but in susceptible skin with various predisposing factors, some bacteria can lead to cutaneous infections.1,9,10,11,12 Impetigo is a contagious infectious dermatosis caused by S. aureus or group A β-haemolytic Streptococcus (GAS) or both.4,13 The most common type of GAS is Streptococcus pyogenes. Individuals of any age can be affected, but children between 2 and 5 years of age are most often involved.1,14 In children, there is no gender predilection, but in adults, men are more commonly affected.2 Globally, the number of children suffering from impetigo at any one time has been estimated to be more than 162 million.1
There are two common forms of impetigo, nonbullous and bullous with distinct causes and clinical appearances.15 A third type that is frequently mentioned in the literature is ecthyma which is basically a deeper ulcerative form of impetigo, although some authors believe it is a unique form of skin infection.6,15 Nonbullous impetigo comprises approximately 70% of all cases and is caused by S. aureus or S. pyogenes.4 Lesions are most often located on the face and extremities. Bullous impetigo is caused by S. aureus and usually takes the appearance of large bullae, which tend to be located in intertriginous areas of the body.4
Etiology and Pathophysiology
Studies have shown that the streptococcal strains responsible for impetigo colonize the unbroken normal skin before the development of skin lesions by an average interval of about 10 days.8 Nonbullous impetigo, also known as impetigo contagiosa, is caused by S. aureus or S. pyogenes.4,13 It is characterized by superficial honey-colored crusted lesions on the face and extremities. The infection is highly contagious and can spread to adjacent areas by auto-inoculation.3,4,14,16 Lesions develop from intradermal inoculation of surface bacteria into broken areas of skin from abrasions, minor trauma, or insect bites. Occasionally, the infection may spread from the skin to the upper respiratory tract after 2 to 3 weeks.2
Bullous impetigo is caused by a toxin produced by S. aureus. It is seen in infants and tends to affect the trunk, extremities, and moist intertriginous areas such as the axillae, neck fold, and diaper area. Lesions are characterized by rapidly enlarging, flaccid bullae that rupture and ooze, revealing a collarette of scales.17 When extensive, skin lesions may be accompanied by systemic symptoms including fever, diarrhea, and generalized weakness.3,4,14,16
Clinical Presentation
Clinically, impetigo presents as either nonbullous or bullous lesions. The nonbullous type is more common and is seen principally in children, although it can occur in adults less frequently.18 Nonbullous impetigo can develop as either a primary or secondary infection and is generally seen on the face or extremities in skin that has been compromised.19 The primary form results from direct inoculation of bacteria into the skin,4 whereas the secondary form is associated with disruption of skin integrity following trauma or underlying dermatologic conditions.4 Lesions usually begin
as maculopapular pustules that evolve to thin-walled vesicles (Figure 72.1A). These tend to rupture, exuding a purulent exudate that forms a characteristic honey-colored crust on an erythematous base (Figure 72.2).4,13 Without treatment, these lesions generally persist for 2 to 3 weeks before resolving without a scar.4,13 Mild regional lymphadenopathy is commonly associated. Systemic symptoms such as fever are typically absent.
as maculopapular pustules that evolve to thin-walled vesicles (Figure 72.1A). These tend to rupture, exuding a purulent exudate that forms a characteristic honey-colored crust on an erythematous base (Figure 72.2).4,13 Without treatment, these lesions generally persist for 2 to 3 weeks before resolving without a scar.4,13 Mild regional lymphadenopathy is commonly associated. Systemic symptoms such as fever are typically absent.
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