Impetigo 

Case

A three year old child comes to your clinic with crusted lesions around the nose with satellite vesicles and pustules. What is the most likely causative organisms and how would you treat this patient?

Impetigo is a very common skin infection affecting mostly young children and adolescents. It is found all over the world and the incidence is greatest in warm humid climates. 

Non-Bullous Impetigo

  1. Usually appears on skin that has been traumatized by burns, chickenpox, insect bites, abrasions, and eczema. 
  2. Most commonly Staphylococcus aureus coag. positive and Streptococcus pyogenes (GABHS). 
  3. Usually starts as a vesicle that develops into a pustule and then forms a honey-colored crust. Heals without scarring. 
  4. Spread is by contact.
  5. The lesions are not pruritic and there are no constitutional symptoms. There may be regional adenopathy.
  6. GABHS may be nephritogenic strain (M types 49, 2, 55, 57, 60) and there is 12% incidence of AGN with these strains. Treatment of impetigo will not prevent AGN and the interval to development of AGN is longer than following acute pharyngitis caused by GABHS.( 1-2 weeks) 
  7. The GABHS causing impetigo have not been associated with acute rheumatic fever.
  8. Staph.aureus causing non-bullous impetigo are not the types associated with toxic shock and scalded skin syndromes.  Emergence of Methacillin Resistant Staphylococcus Aureus (MRSA)
  9. Differential Diagnosis
    1. Herpes skin infections- usually in clusters and have prodrome of pain or itching.
    2. Tinea corporis
    3. scabies that has become crusted by scratching or has become impetiginized. 
    4. lice infestation of the scalp that has lead to itching and secondary infection develops.
Bullous Impetigo
  1. More common in young children and infants. 
  2. The etiology is Staphylococcus aureus coag.positive, the same types that are associated with toxic shock and scalded skin syndromes. 
  3. Bulla develop on previously intact skin and cause a clear fluid blister that ruptures easily. Aspirate of fluid will grow Staph. Heals without scarring.
Complications
  1. Rarely osteomyelitis, septic joints, or septicemia
  2. Positive blood cultures unusual
  3. develop cellulitis in 10% of cases
  4. With strep may get lymphangitis, scarlet fever, and AGN.
Management 
  1. Mupirocin (Bactroban)- topical antibiotic effective vs. Strep and Staph. Apply three times daily for 7-10 days. May need to soften crusts prior to applying with moist cloth.  Rare bacterial resistance.
  2. Topical Neosporin
  3. With widespread disease or lesion in areas difficult to put topical antibiotic on, oral antibiotic may be preferable for 7-10 days
    4.     a. If MRSA a consideration, Clindamycin should be used.
    References
    1. Bisno, Alan and Stevens, Dennis. Streptococcal Infections of Skin and Soft Tissues. NEJM Vol 334 No 4 Jan 25, 1996 240-45
    2. Lookingbill, Donald. Impetigo. Pediatrics in Review December 1985
    3. Cole C, and Gazwood J. Diagnosis and Treatment of Impetigo. American Family Physician. March 15, 2007