Strep Skin Infection (Impetigo) – A Comprehensive Guide
Overview
Impetigo is a highly contagious superficial bacterial skin infection most often caused by Streptococcus pyogenes (group A streptococcus) or Staphylococcus aureus. While the term “impetigo” usually refers to the classic honey‑colored crusted lesions, the infection can appear in several forms, ranging from tiny vesicles to large, oozing patches.
- Who it affects: Children aged 2–5 years are the most commonly affected group, but adults—especially those with skin breaks, eczema, or compromised immunity—can also develop impetigo.
- Prevalence: In the United States, impetigo accounts for roughly 5–10 % of all pediatric skin complaints and is responsible for about 150,000–200,000 outpatient visits each year.[1] CDC, 2023
- Geography: Outbreaks are more frequent in warm, humid climates and in settings where close contact is common (day‑care centers, schools, sports teams).
Symptoms
Impetigo typically develops over 1–3 days after the bacteria enter the skin. The presentation can be divided into two classic types:
Non‑bullous (crusted) impetigo
- Small, red papules that quickly become vesicles.
- Vesicles rupture, leaving a thin, honey‑yellow crust.
- Lesions often appear on the face (especially around the nose and mouth), arms, and diaper area.
- Itching or mild tenderness is common.
Bullous impetigo
- Larger, fluid‑filled blisters (bullae) with clear or yellowish fluid.
- Bullae usually arise on the trunk, abdomen, or extremities.
- After bursting, the skin may develop a glossy, eroded surface that can crust over.
General symptoms (less common)
- Fever (often low‑grade) – seen more often in extensive disease.
- Swollen lymph nodes near the affected area.
- General feeling of malaise, especially in children.
Causes and Risk Factors
Impetigo occurs when bacteria breach the outer skin barrier. The most frequent routes are:
Primary causes
- Group A Streptococcus (GAS) – produces enzymes that facilitate skin invasion.
- Staphylococcus aureus – especially methicillin‑sensitive strains; MRSA can also cause impetigo but is less common.
Risk factors
- Age: Young children have thinner skin and are more prone to skin trauma.
- Skin injury: Cuts, scratches, insect bites, or any dermatitis (eczema, atopic dermatitis) provide an entry point.
- Close contact settings: Day‑care centers, schools, sports teams, military barracks.
- Warm, humid environment: Moisture promotes bacterial growth.
- Immunocompromised states: HIV, chemotherapy, chronic steroids.
- Poor hygiene: Infrequent hand‑washing or bathing increases bacterial load.
Diagnosis
Diagnosis is primarily clinical, based on the characteristic appearance of lesions. However, certain situations require laboratory confirmation.
Clinical evaluation
- Visual inspection of the crusted or bullous lesions.
- History taking (onset, exposure to others with impetigo, recent skin trauma).
Laboratory tests
- Gram stain & bacterial culture: Swab the base of a lesion after gently removing the crust. Culturing helps identify the organism (GAS vs. S. aureus) and guides antibiotic choice, especially if MRSA is suspected.
- Rapid antigen detection test (RADT) for GAS: Provides results in minutes and is useful when streptococcal involvement is suspected.
- Blood tests: Rarely needed, but a CBC may be ordered if systemic infection is suspected.
Treatment Options
Most cases resolve within 1–2 weeks with appropriate therapy. Treatment goals are to eradicate bacteria, limit spread, and prevent complications.
Topical antibiotics
- Mupirocin 2 % ointment: Applied three times daily for 5 days; first‑line for <5 cm lesions.
- Retapamulin 1 % ointment: Another option, used twice daily for 5 days.
- Topicals are preferred for limited disease because they have fewer systemic side effects.
Oral antibiotics
Indicated for extensive disease, lesions on the scalp, mucous membranes, or when topical therapy fails.
- For presumed GAS: Penicillin V 500 mg QID or Amoxicillin 500 mg TID for 7–10 days.
- If S. aureus is suspected or confirmed: Cephalexin 500 mg QID or Dicloxacillin 500 mg QID.
- MRSA‑suspected cases: Trimethoprim‑sulfamethoxazole (TMP‑SMX) 800/160 mg BID, Clindamycin 300 mg QID, or Doxycycline 100 mg BID (≥8 y).
Adjunctive measures
- Wound care: Gently clean lesions with mild soap and water, pat dry, then apply prescribed medication.
- Covering lesions: Loose, breathable dressings can reduce spread but avoid occlusive bandages that trap moisture.
- Hygiene education: Frequent hand‑washing, keeping nails short, and avoiding sharing towels or clothing.
Living with Strep Skin Infection (Impetigo)
While treatment is usually straightforward, day‑to‑day management helps speed recovery and prevents spread.
Daily care tips
- Keep the area clean: Wash twice daily with mild soap; rinse well.
- Apply medication exactly as prescribed: Missing doses can prolong infection and increase resistance.
- Change dressings daily: Use clean, non‑adhesive gauze if needed.
- Avoid scratching: Trim nails and consider wearing gloves at night for children.
- Separate personal items: Towels, pillowcases, and clothing should be laundered daily in hot water (≥60 °C/140 °F).
- Stay hydrated and maintain nutrition: Good overall health supports immune function.
School or daycare considerations
- Notify caregivers/teachers of the diagnosis.
- Children can usually return to school after 24 hours of appropriate antibiotic therapy and when lesions are covered.
- Encourage frequent hand‑washing among peers.
Prevention
Because impetigo spreads easily, preventive strategies are essential, especially in settings with many children.
- Hand hygiene: Wash hands with soap for at least 20 seconds after touching any skin lesion.
- Prompt treatment of minor skin injuries: Clean cuts or scrapes immediately with antiseptic solution.
- Manage chronic skin conditions: Keep eczema moisturized and treat flares early.
- Avoid sharing personal items: Towels, razors, clothing, and sports equipment.
- Environmental control: Keep living spaces dry; use fan or dehumidifier in humid climates.
- Vaccination: While no vaccine exists for impetigo, routine immunizations (e.g., influenza, COVID‑19) reduce overall infection burden and secondary skin complications.
Complications
When left untreated or inadequately treated, impetigo can lead to serious issues.
- Cellulitis: Deeper skin infection causing swelling, redness, and pain; may require intravenous antibiotics.
- Post‑streptococcal glomerulonephritis (PSGN): An immune‑mediated kidney inflammation that can develop after GAS infection (≈0.5–1 % of cases). Presents with hematuria, edema, and hypertension.[2] NIH, 2022
- Ecthyma: A deeper ulcerating form that can scar.
- Scarring and pigment changes: Especially if lesions are picked or infected for prolonged periods.
- Systemic infection (bacteremia, sepsis): Rare but possible in immunocompromised patients.
When to Seek Emergency Care
Call 911 or go to the nearest emergency department if you notice any of the following:
- Rapid spreading of redness, swelling, or pain beyond the original lesions.
- High fever (≥38.5 °C / 101.3 °F) accompanied by chills.
- Severe pain, especially if accompanied by difficulty moving a limb.
- Signs of a systemic infection: rapid heart rate, low blood pressure, confusion, or dizziness.
- Sudden onset of dark urine, facial swelling, or reduced urine output (possible kidney involvement).
- Rapid breathing or shortness of breath.
References
- Centers for Disease Control and Prevention. Impetigo – Clinical Overview. Updated 2023. https://www.cdc.gov/impetigo
- National Institute of Diabetes and Digestive and Kidney Diseases. Post‑streptococcal glomerulonephritis. Updated 2022. https://www.niddk.nih.gov/health-information/kidney-disease/post-streptococcal-glomerulonephritis
- Mayo Clinic. Impetigo (skin infection). 2024. https://www.mayoclinic.org/diseases-conditions/impetigo
- Cleveland Clinic. Impetigo: Symptoms, causes, and treatment. 2024. https://my.clevelandclinic.org/health/diseases/21071-impetigo
- World Health Organization. Antimicrobial resistance: Global report on surveillance. 2021. https://www.who.int/publications/i/item/9789241565710