Overview
Definition:
Impetigo is a superficial bacterial skin infection commonly affecting infants and children
It is characterized by the formation of pustules or vesicles that rupture to form characteristic honey-colored crusts
It is broadly classified into nonbullous and bullous forms, with distinct clinical presentations and etiologic agents.
Epidemiology:
Impetigo is one of the most common bacterial skin infections in children worldwide, with a peak incidence in children aged 2 to 5 years
It is highly contagious and spreads rapidly in crowded environments such as daycares and schools
Poor hygiene and minor skin trauma are predisposing factors
Bullous impetigo is less common than nonbullous impetigo and is predominantly caused by Staphylococcus aureus.
Clinical Significance:
Prompt and accurate diagnosis and management of impetigo are crucial to prevent complications such as cellulitis, lymphadenitis, and post-streptococcal glomerulonephritis (especially with S
pyogenes)
Understanding the differences between bullous and nonbullous forms guides appropriate antibiotic selection and treatment duration
This knowledge is vital for pediatric residents preparing for DNB and NEET SS examinations.
Clinical Presentation
Symptoms:
Nonbullous impetigo: Initially presents as small red papules that rapidly develop into vesicles or pustules
These rupture easily, leaving a moist, erythematous base that dries into characteristic honey-colored crusts
Lesions are often found on the face, especially around the nose and mouth
Pruritus is common
Bullous impetigo: Characterized by flaccid, thin-roofed bullae filled with clear or cloudy fluid, which may become hemorrhagic
Bullae rupture quickly, leaving a raw, erythematous base
Lesions are often found on the trunk, limbs, and extremities, and are less frequently associated with itching
Systemic symptoms like fever are rare in uncomplicated impetigo.
Signs:
Nonbullous impetigo: Superficial erosions with characteristic greasy, golden-yellow crusting
Lack of significant inflammation or pain unless secondarily infected
Bullous impetigo: Superficial blisters or bullae, ranging from a few millimeters to several centimeters in diameter
Bullae rupture easily, exposing an erythematous base
Positive Nikolsky sign may be present in severe cases or related conditions like staphylococcal scalded skin syndrome (SSSS).
Diagnostic Criteria:
Diagnosis of impetigo is primarily clinical, based on characteristic appearance of lesions and epidemiological context
Laboratory investigations are usually not required for typical cases but may be helpful in severe or refractory cases
Culture and sensitivity testing from exudate or bulla fluid can confirm the causative organism and guide antibiotic therapy, especially in cases of treatment failure or suspected resistance.
Diagnostic Approach
History Taking:
Key history points include the onset and progression of skin lesions, presence of itching or pain, history of recent exposure to others with similar lesions, presence of minor skin trauma or insect bites, and any history of atopic dermatitis or eczema
Inquire about recent antibiotic use and allergies
For bullous impetigo, ask about any fever or systemic symptoms.
Physical Examination:
A thorough dermatological examination is essential
Assess the morphology of the lesions (papules, vesicles, pustules, bullae, crusts), distribution and extent of the rash
Look for signs of secondary bacterial infection (erythema, warmth, tenderness) or complications like cellulitis
Examine lymph nodes for regional lymphadenopathy
Differentiate from other vesicular and bullous disorders.
Investigations:
Gram stain and bacterial culture of vesicle fluid or crust exudate are indicated for recurrent, severe, or unresponsive cases, or when MRSA is suspected
This helps identify the causative organism (Staphylococcus aureus, Streptococcus pyogenes, or mixed flora) and guide antibiotic selection
Rapid antigen detection tests may be available for S
pyogenes
Blood tests are rarely needed unless systemic symptoms or complications are present.
Differential Diagnosis:
Differential diagnoses for nonbullous impetigo include herpes simplex virus (HSV) infection, varicella, allergic contact dermatitis, and insect bites
For bullous impetigo, differentials include bullous impetigo, staphylococcal scalded skin syndrome (SSSS), epidermolysis bullosa, bullous drug eruptions, and herpes zoster
Differentiating features include the character of the bullae, presence of systemic symptoms, and distribution of lesions.
Management
Initial Management:
The primary goal is to prevent spread and complications
Gentle cleansing of lesions with mild soap and water to remove crusts is recommended
Topical antibiotics are often the first-line treatment for limited disease
Systemic antibiotics are indicated for more widespread disease, bullous impetigo, or if there are signs of secondary infection or systemic involvement.
Medical Management:
Topical antibiotics: Mupirocin 2% ointment or cream applied TID for 5-7 days is highly effective for localized nonbullous impetigo
Retapamulin ointment is another option
Systemic antibiotics for nonbullous impetigo: Oral cephalexin (15-25 mg/kg/day divided TID-QID), erythromycin (30-40 mg/kg/day divided TID-QID), or azithromycin (10 mg/kg on day 1, then 5 mg/kg/day for 4 days) are options
For bullous impetigo and suspected MRSA: Oral clindamycin (10-13 mg/kg/day divided TID) or trimethoprim-sulfamethoxazole (8-10 mg/kg/day divided BID) may be used
Duration of systemic therapy is typically 7 days, though longer courses may be necessary for complicated cases.
Surgical Management:
Surgical intervention is generally not required for impetigo
However, in cases of severe secondary infection, abscess formation, or extensive necrotic lesions, surgical debridement may be considered by a specialist
Wound care and drainage are paramount in such scenarios.
Supportive Care:
Emphasis on strict hygiene measures: frequent hand washing for patient and caregivers, cleaning of shared surfaces, and keeping children home from school or daycare until lesions are crusted over and not weeping
Educate parents on proper wound care and signs of worsening infection
Good nutritional support is important for overall health and recovery.
Complications
Early Complications:
Cellulitis: Spread of infection to deeper tissues, presenting as erythema, warmth, swelling, and pain
Lymphadenitis: Swollen and tender regional lymph nodes
Otitis externa: Secondary infection of the external ear canal
Bacteremia: Rare, but can lead to sepsis, especially in immunocompromised individuals.
Late Complications:
Post-streptococcal glomerulonephritis (PSGN): Can occur 1-3 weeks after S
pyogenes infection, even if skin lesions have healed
Symptoms include hematuria, edema, and hypertension
Scarlet fever: If the impetigo is caused by an erythrogenic toxin-producing strain of S
pyogenes
Scarring: Usually minimal with nonbullous impetigo
bullous impetigo can occasionally lead to minor scarring.
Prevention Strategies:
Promoting good personal hygiene, including regular hand washing and keeping fingernails short
Prompt treatment of minor skin abrasions, insect bites, and other dermatoses
Isolation of infected individuals from close contacts until they are no longer contagious (lesions crusted and dry)
Educating the public about the contagious nature of impetigo and methods of transmission.
Prognosis
Factors Affecting Prognosis:
Prompt and appropriate antibiotic treatment generally leads to a good prognosis with complete resolution
Factors that may negatively impact prognosis include delayed treatment, underlying immunocompromise, development of complications, and antibiotic resistance.
Outcomes:
With appropriate management, impetigo typically resolves within 7-14 days
Most cases of nonbullous impetigo heal without scarring
Bullous impetigo may be associated with transient hyperpigmentation or depigmentation but typically heals well
Complications like PSGN are usually self-limiting but require monitoring.
Follow Up:
Follow-up is generally not required for uncomplicated impetigo once treatment is completed and lesions are resolving
However, follow-up is recommended for cases with complications such as cellulitis or suspected PSGN
Patients with recurrent impetigo may benefit from screening for nasal carriage of S
aureus and strategies to decolonize.
Key Points
Exam Focus:
Distinguish bullous from nonbullous impetigo
Identify common causative organisms (S
aureus, S
pyogenes)
Recall first-line topical (mupirocin) and systemic (cephalexin, azithromycin) antibiotics
Recognize indications for systemic therapy (widespread, bullous, complications)
Remember potential complications like PSGN
Understand hygiene and isolation measures.
Clinical Pearls:
Honey-colored crusts are pathognomonic for impetigo
Bullous impetigo often caused by S
aureus
Topical mupirocin is very effective for localized disease
Systemic antibiotics are necessary for bullous form
Emphasize hand hygiene and keeping children out of school until lesions dry
Always consider MRSA in recurrent or severe cases and choose appropriate antibiotics.
Common Mistakes:
Mistaking impetigo for fungal infections or eczema and delaying appropriate antibiotic treatment
Prescribing systemic antibiotics for mild, localized nonbullous impetigo without adequate trial of topical therapy
Inadequate duration of antibiotic therapy leading to relapse or complications
Failing to consider MRSA in treatment-resistant cases
Not emphasizing adequate hygiene measures to prevent spread.