How Long is Impetigo Contagious?
Impetigo remains contagious until 24 hours after starting appropriate antimicrobial therapy, or until the lesions are no longer present if left untreated. 1
Understanding Impetigo and Its Contagious Period
Impetigo is a highly contagious bacterial skin infection affecting the superficial layers of the epidermis. It presents in two main forms:
- Nonbullous impetigo (70% of cases): Characterized by honey-colored crusts, caused by Staphylococcus aureus or Streptococcus pyogenes
- Bullous impetigo (30% of cases): Presents with flaccid bullae, caused exclusively by toxin-producing strains of S. aureus
Contagious Period and Transmission
- Impetigo is most contagious during the period when fluid is actively weeping from lesions
- The infection spreads through:
- Direct contact with lesions
- Contact with items contaminated by fluid from lesions (towels, clothing, toys)
- Autoinoculation (spreading to other parts of the body)
Return to Normal Activities
According to the Infectious Diseases Society of America guidelines, athletes with skin infections caused by Group A Streptococcus (including impetigo) should not return to competitive sports for at least 24 hours after beginning appropriate oral antimicrobial therapy 2. This principle applies to all individuals with impetigo, including children returning to school or daycare.
Treatment Options and Impact on Contagiousness
Topical Treatment
- First-line for limited disease: Mupirocin or retapamulin applied twice daily for 5 days 1
- Topical therapy is effective in reducing contagiousness within 24 hours of initiation
Oral Antibiotics
- For extensive disease: 7-day regimen with agents active against S. aureus 1
- For MSSA: Dicloxacillin or cephalexin
- For suspected MRSA: Doxycycline, clindamycin, or trimethoprim-sulfamethoxazole
Important Caveats
- Penicillin alone is not effective for impetigo treatment 1
- Without treatment, impetigo typically resolves within 2-3 weeks 3, but remains contagious throughout this period
- Rising rates of antibiotic resistance may affect treatment efficacy and potentially extend the contagious period if initial therapy fails 4
Prevention of Transmission
To prevent spreading impetigo to others:
- Maintain good hygiene practices
- Avoid sharing personal items like towels, clothing, or bedding
- Cover lesions with bandages if possible
- Wash hands frequently, especially after touching lesions
- Clean and disinfect surfaces that may have come in contact with lesions
- Avoid close contact activities until 24 hours after starting treatment
Special Considerations
- In outbreaks (such as in sports settings), prompt identification and isolation of infected individuals for at least 24 hours after treatment initiation is crucial 2
- For children in daycare or school settings, the same 24-hour rule applies before returning to these environments
- Bacterial cultures should be obtained before initiating therapy in cases of treatment failure or recurrent infections 1
Impetigo typically heals without scarring, though it may leave temporary depigmented areas. Complications are rare, with poststreptococcal glomerulonephritis being the most serious potential consequence 3.