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 or impetigo contagiosa is a contagious superficial bacterial skin infection most frequently encountered in children. It is typically classified as either primary (e.g. direct bacterial invasion of previously normal skin), secondary, or common impetigo (where the infection is secondary to some other underlying skin disease that disrupts the skin barrier, such as scabies or eczema).

Impetigo is also classified as bullous or non-bullous impetigo. Bullous impetigo simply means that the skin eruption is characterised by bullae (blisters).

The term 'impetigo contagiosa' is sometimes used to mean non-bullous impetigo, and at other times it is used as a synonym for all impetigo.

Non-Bullous Impetigo (70% of cases)

  1. Usually appears on skin that has been traumatized by burns, chickenpox, insect bites, abrasions, and atopic dermatitis. 
  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 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) has altered treatment although most Staph causing impetigo are not 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 (secondarily infected)
    4. lice infestation of the scalp that has lead to itching and secondary infection develops.

Bullous Impetigo

Bullous impetigo after the bulla have broken

  1. More common in  infants and young children
  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.
  4. DDx- Stevens Johnson Syndrome, erythema multiforme, dermatitis herpetiformis.

Secondary Impetigo

  1. Secondary impetigo may occur as a complication of many dermatological conditions (notably eczema).
  2. The eruption appears clinically similar to non-bullous impetigo.
  3. Usually S. aureus is involved.
  4. The underlying skin disease may improve with successful treatment of the impetigo, and the converse may also be true.


  1. Rarely osteomyelitis, septic joints, or septicemia
  2. Positive blood cultures unusual
  3. Development of cellulitis in 10% of cases
  4. With strep may get lymphangitis, scarlet fever, AGN. and pneumonia


  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
    1. If MRSA a consideration, Clindamycin should be used.
    2. Could try Cephelexin and Augmentin if not thinking MRSA.


  1. Koning S, van der Sande R, Verhagen AP, et al. Interventions for impetigo. Cochrane Database Syst Rev 2012; 1:CD003261.
  2. Bisno, Alan and Stevens, Dennis. Streptococcal Infections of Skin and Soft Tissues. NEJM Vol 334 No 4 Jan 25, 1996 240-45
  3. Lookingbill, Donald. Impetigo. Pediatrics in Review December 1985
  4. Cole C, and Gazwood J. Diagnosis and Treatment of Impetigo. American Family Physician. March 15, 2007
  5. Mooulin F, et al. Managing children skin and soft tisue infections.  Arch Pediatrics.  Oct 2008;15 Suppl 2: S 62-67