What is impetigo, and how can you recognize it?
Impetigo is a superficial, highly contagious skin infection caused by pyogenic bacteria: *Staphylococcus aureus* in the vast majority of cases in France and, more rarely, *Streptococcus pyogenes* (group A β-hemolytic streptococcus), either alone or in combination. It is the most common bacterial skin infection inchildren, particularly between the ages of 2 and 5, but it can also affect adults.
Typical signs:
- Lesions often begin around body orifices (mouth, nostrils, ears) or at sites of minor skin abrasions.
- Erythematous macules that develop into superficial vesicles or pustules.
- The vesicles rupture quickly, leaving a clear exudate that dries to form characteristic honey-colored crusts.
- Moderate itching, sometimes accompanied by pain on pressure.
- No fever or change in general condition in mild cases.
- Satellite lymphadenopathy may occur.
On pre-existing atopic skin (eczema), this is referred to asimpetiginization: a bacterial superinfection of a pre-existing skin condition.
How does impetigo spread?
Impetigo is transmitted primarily through:
- Direct contact with skin lesions or secretions from an infected person.
- Indirect contact via contaminated objects: towels, washcloths, sheets, clothing, toys, hairbrushes, and sports equipment.
- Self-inoculation through scratching: spread of lesions to other areas of the same person’s body.
- The incubation period is generally 1 to 3 days after exposure (up to 10 days).
- Asymptomatic nasal carriage of *Staphylococcus aureus* (in 20 to 30% of the general population) is a reservoir that must be considered to explain recurrences.
Childcare settings (daycare centers, preschools, after-school programs) and large households are prime settings for transmission.
What are the treatments for impetigo?
Treatment consists of antibiotic therapy tailored to the severity of the infection, as prescribed by a doctor, and thorough local care (HAS 2021 recommendations):
- Localized forms (few lesions, limited area):
- Prescription topical antibiotics: mupirocin ointment (Mupiderm) or fusidic acid cream or ointment (Fucidine), 2 to 3 applications per day for 5 days.
- Local care: Soften scabs with water and mild soap, remove gently, and pat dry.
- An adjunctive antiseptic (aqueous chlorhexidine) may be used as part of overall care.
- Extensive, bullous, or multifocal forms, with systemic symptoms or in high-risk patients:
- Prescription oral antibiotic therapy: pristinamycin, amoxicillin + clavulanic acid, or macrolides (clarithromycin, josamycin) in case of penicillin allergy. Usual duration: 7 days.
- Associated local care.
- Care recommended for all forms:
- Daily cleansing with water and mild soap or syndet.
- Keep nails short (to limit self-inoculation).
- Frequent handwashing, especially after contact with lesions.
- Cover accessible lesions with dressings to limit spread.
- Nasal decolonization with mupirocin nasal ointment (Bactroban): to be discussed in cases of recurrence, after detection of nasal carriage of *Staphylococcus aureus*. Treatment may also extend to household members.
Avoid: applying topical corticosteroids (which can worsen the condition), occlusive ointments on scabs (which delay drying), and topical antibiotics used without a prescription or contrary to recommendations (risk of resistance).
How can impetigo be prevented?
Prevention is based on a few simple and effective principles:
- Regular handwashing with soap and water, especially after contact with an infected person or after blowing your nose.
- Keep nails short and clean.
- Immediately disinfect any small skin wounds (scrapes, insect bites, cuts).
- Do not share personal items: towels, washcloths, bath towels, hairbrushes, or hats.
- Maintain good skin hydration to preserve the skin’s barrier function (especially in children with atopic skin).
- Cover open wounds while they are healing.
- Wash the laundry of infected individuals at a minimum of 60°C, ideally separately.
- Disinfect frequently touched surfaces and objects if there is a case in the household.
- Treat any chronic nasal colonization if there is a family history of recurrence.
Can impetigo recur?
Yes, recurrences of impetigo are possible, particularly in:
- People who are chronic carriers of *Staphylococcus aureus* in the nose, perineal area, or armpits (reservoirs).
- Children in group settings.
- People living in crowded conditions or where good hygiene is difficult to maintain.
- Patients with underlying skin conditions (eczema, scabies, chickenpox) that serve as entry points for the infection.
- Immunocompromised individuals or those with poorly controlled diabetes.
In cases of frequent recurrences, the doctor may recommend testing for nasal carriage (swab test), decolonization treatment with mupirocin nasal ointment, and, if necessary, coordinated treatment for other household members who are carriers.
What is the difference between bullous and non-bullous impetigo?
Two main clinical forms are described:
- Non-bullous (crusted) impetigo: the most common form (70 to 80% of cases). Superficial vesicles and pustules that rapidly evolve into honeycomb crusts. Preferentially located around orifices. Caused primarily by *Staphylococcus aureus* (sometimes associated with *Streptococcus pyogenes*).
- Bullous impetigo: a specific form associated with strains of *Staphylococcus aureus* that produce exfoliative toxins (ETA, ETB). Vesicles progress to large, flaccid blisters containing a yellowish, then purulent fluid; they rupture easily, leaving erosions with a red base and an epidermal rim. Preferential locations include the trunk, buttocks, and perineum. More common in newborns and infants.
- Ecthyma: a deep-seated form of impetigo (deep ulcerated lesions covered by a thicker crust), progressing over weeks, with possible scarring. More common in compromised adults (immunocompromised, diabetic, or living in precarious conditions).
A severe form to be recognized in infants: staphylococcal scalded skin syndrome (SSSS), caused by systemic spread of exfoliative toxins. Generalized epidermal detachment, fever, irritability, and dehydration. **Pediatric hospital emergency** in children under 5 years of age.
What are the risk factors for impetigo?
Several factors increase the risk:
- Age: children aged 2 to 5 years, a period of socialization in group settings.
- Hot and humid climate, summer, excessive sweating.
- Close contact (large households, schools, daycare centers, recreation centers, camps).
- Minor skin breaks: insect bites, scrapes, cuts, and scratches.
- Pre-existing skin conditions: atopic eczema, scabies, head lice, chickenpox, irritant dermatitis—conditions that predispose to impetigo.
- Poor hygiene, limited access to water.
- Chronic carriage of *S. aureus* (nasal, axillary, perineal).
- Immunodeficiency, uncontrolled diabetes.
- Participation in contact sports (wrestling, judo, rugby) involving shared equipment.
Can you go to school or work with impetigo?
Impetigo is a contagious infection subject toexclusion rules in France:
- Mandatory exclusion from daycare, school, or community settings for at least 72 hours after the start of effective antibiotic treatment (recommendations from the French High Council for Public Health).
- If the lesions are few in number and localized, some institutions allow a return to school or work provided the lesions are covered with occlusive dressings and cannot be touched.
- A doctor may issue a certificate of non-contagiousness once the exclusion period has ended.
- At home: Avoid close contact with other household members, particularly infants and immunocompromised individuals.
- Wash hands frequently, keep nails short, and do not share linens or personal items.
For babies and infants: monitor them closely; seek prompt medical attention in case of fever, rapid spread of lesions, or deterioration in general health.
How is impetigo diagnosed?
The diagnosis is primarily clinical:
- Visual examination of characteristic lesions (vesicopustules, honeycomb crusts, blisters).
- Medical history: age, context (group setting, household, atopic predisposition, pre-existing wounds).
- Bacteriological culture with antibiotic susceptibility testing: not routinely performed, but indicated in cases of treatment failure, recurrence, severe or atypical forms, or suspected MRSA (methicillin-resistant Staphylococcus aureus).
- Blood tests are usually not necessary in uncomplicated cases; order them if there are systemic symptoms or suspected complications.
- Test for nasal carriage in cases of recurrence.
- Differential diagnosis: cutaneous herpes (clustered vesicles), shingles (involvement of a single dermatome), superficial burn, seborrheic dermatitis in infants, impetiginized scabies, and secondary infection of chickenpox.
What are the possible complications of impetigo?
Although most cases of impetigo resolve favorably with proper treatment, several complications are possible:
- Cellulitis (bacterial dermo-hypodermitis): deep spread of the infection, extensive warm red patch, fever—seek prompt medical attention.
- Lymphangitis: an ascending red streak originating from the lesion, sometimes accompanied by satellite lymphadenopathy.
- Bacteremia/sepsis: bacterial spread; rare but severe, especially in immunocompromised patients and infants.
- Acute post-streptococcal glomerulonephritis: a late complication (2 to 3 weeks after the *Streptococcus pyogenes* infection) characterized by edema, gross hematuria, and hypertension. Urinary monitoring is recommended in children, particularly in cases of extensive or multifocal disease.
- Staphylococcal Scalded Skin Syndrome (SSSS): a pediatric emergency in infants and young children—generalized epidermal detachment, fever, hospitalization.
- Staphylococcal toxic shock: rare, life-threatening emergency.
- Recurrences may occur in cases of chronic carriage or uncorrected predisposing factors.
- See also “Infected Wounds” for general care principles and “Itching” for useful anti-scratching advice during the healing phase.
Any rapid worsening of symptoms, fever, malaise, or systemic signs warrants immediate medical attention. Prompt consultation is also recommended for infants, pregnant women, immunocompromised individuals, or people with diabetes.
