Overview
Definition:
Impetigo is a highly contagious superficial bacterial skin infection, primarily affecting infants and young children
It is characterized by the formation of pustules or vesicles that rupture to form characteristic honey-colored crusts.
Epidemiology:
It is the most common bacterial skin infection in children, with an incidence of approximately 1.4 per 1000 children per year in temperate climates
Outbreaks are common in daycare centers and schools
It is more prevalent in warmer, humid conditions and in areas with poor hygiene.
Clinical Significance:
While generally a benign condition, impetigo can lead to significant morbidity if untreated due to complications such as cellulitis, abscess formation, and post-streptococcal glomerulonephritis
Appropriate antibiotic management is crucial to prevent spread and complications, making it a common topic in pediatric residency training and board examinations.
Clinical Presentation
Symptoms:
Pruritus is a common symptom
Lesions often begin as small red spots that quickly develop into blisters (vesicles) or pus-filled sacs (pustules)
These lesions rupture easily, leaving moist, erythematous erosions that dry to form characteristic yellowish-brown ("honey-colored") crusts
Lesions are typically found on the face, especially around the nose and mouth, but can spread to other areas of the body.
Signs:
Erythematous base with vesicles, pustules, or bullae
Superficial erosions with characteristic honey-colored crusting
Regional lymphadenopathy may be present
Bullous impetigo presents with larger, flaccid bullae.
Diagnostic Criteria:
Diagnosis is primarily clinical, based on the characteristic appearance of the lesions
Laboratory confirmation is usually not necessary unless there is suspicion of antibiotic resistance, severe infection, or atypical presentation
Cultures may be obtained from the base of a ruptured vesicle or pustule to identify the causative organism and guide antibiotic therapy.
Diagnostic Approach
History Taking:
Inquire about the onset and progression of skin lesions
Ask about recent exposure to individuals with similar rashes, daycare or school attendance, hygiene practices, and any history of atopy or eczema
Assess for fever or systemic symptoms, which may suggest a more severe infection or complication.
Physical Examination:
Examine the skin for characteristic lesions: vesicles, pustules, bullae, and honey-colored crusts
Note the distribution and extent of the rash
Palpate for regional lymphadenopathy
Assess for signs of systemic illness like fever or lethargy.
Investigations:
Microscopic examination of Gram-stained smears of the exudate can provide rapid preliminary identification of bacteria (e.g., Gram-positive cocci in clusters suggestive of Staphylococcus aureus
Gram-positive cocci in chains suggestive of Streptococcus pyogenes)
Bacterial culture and sensitivity testing are recommended for recurrent infections, treatment failures, or suspected methicillin-resistant Staphylococcus aureus (MRSA).
Differential Diagnosis:
Eczema herpeticum, varicella, herpes simplex virus infection, fungal infections (e.g., tinea), insect bites, scabies, and contact dermatitis should be considered
The honey-colored crust is a key distinguishing feature of impetigo.
Management
Initial Management:
Gentle cleansing of lesions to remove crusts is essential before applying topical antibiotics
This promotes better penetration and reduces the bacterial load
Patients should be advised on good hygiene practices to prevent spread.
Medical Management:
Topical antibiotics are the treatment of choice for localized, non-bullous impetigo
Mupirocin 2% ointment or cream applied three times daily for 5-7 days is highly effective
Retapamulin 1% ointment can also be used
For widespread disease, bullous impetigo, or suspected MRSA, oral antibiotics are indicated
First-line oral antibiotics include cephalexin 25-50 mg/kg/day divided into 3-4 doses, or cefadroxil 30 mg/kg/day divided into 2 doses
For suspected MRSA, trimethoprim-sulfamethoxazole (TMP-SMX) 8-12 mg/kg/day in two divided doses, or clindamycin 10-20 mg/kg/day in three divided doses (max 1.8 g/day) are options
Treatment duration is typically 7-10 days.
Surgical Management:
Surgical intervention is generally not required for impetigo
However, in cases of complicated infections leading to cellulitis, abscesses, or ecthyma, incision and drainage may be necessary
These are less common presentations.
Supportive Care:
Educate parents and caregivers about contagion and the importance of completing the full course of antibiotics
Advise on keeping fingernails short to prevent scratching and autoinoculation
Ensure adequate hand hygiene for all family members
Children should be kept out of school or daycare until they have received at least 24-48 hours of antibiotic treatment and their lesions are no longer weeping or crusted.
Complications
Early Complications:
Cellulitis, lymphadenitis, and superficial abscesses are common early complications
Rarely, ecthyma (a deeper form of impetigo) may develop.
Late Complications:
Post-streptococcal glomerulonephritis can occur 1-3 weeks after S
pyogenes infection, even if the skin infection appears resolved
Although rare, deep tissue infections, bacteremia, and sepsis can occur in immunocompromised individuals
Scarring is uncommon with superficial impetigo but can occur with deeper infections or excoriation.
Prevention Strategies:
Prompt treatment of minor skin abrasions and insect bites can prevent initial infection
Maintaining good personal hygiene, including frequent handwashing, is crucial
Educating affected individuals and their families on hygiene practices and avoiding close contact with others can limit transmission.
Prognosis
Factors Affecting Prognosis:
Prompt and appropriate antibiotic treatment generally leads to a good prognosis
Factors negatively impacting prognosis include delayed treatment, immunocompromised status, poor hygiene, and the development of complications.
Outcomes:
With adequate treatment, impetigo typically resolves within 7-10 days, with minimal or no scarring
Recurrence is possible if hygiene is poor or there is continued exposure to infected individuals.
Follow Up:
Follow-up is usually not required for uncomplicated cases of impetigo treated appropriately
However, if lesions do not improve within 7-10 days, or if there are signs of complications, further evaluation and treatment adjustment are necessary
Monitor for signs of post-streptococcal glomerulonephritis, particularly in cases of suspected S
pyogenes infection.
Key Points
Exam Focus:
Distinguish between non-bullous and bullous impetigo
Understand the typical causative organisms (Staphylococcus aureus, Streptococcus pyogenes)
Recognize the characteristic honey-colored crust
Know first-line topical (mupirocin) and oral (cephalexin, cefadroxil) antibiotic choices
Be aware of MRSA coverage (TMP-SMX, clindamycin) and indications for oral therapy.
Clinical Pearls:
Always gently debride crusts before applying topical therapy to enhance efficacy
Consider MRSA in recurrent cases, treatment failures, or outbreaks in close-contact settings like schools or sports teams
Educate parents on hygiene to prevent spread within the household.
Common Mistakes:
Underestimating the contagiousness and failing to advise on hygiene
Prescribing topical antibiotics for extensive or bullous impetigo without considering oral agents
Inadequate duration of antibiotic therapy leading to recurrence or complications
Not considering MRSA in appropriate clinical scenarios.