The Case

A toddler presents to the ED with a rash on their face. The patient’s father is concerned because he personally had a “boil that needed to be drained last month. He is requesting a prescription for antibiotics. The rash is shown here.

a skin infection… probably

The Diagnosis

This is, of course, our old friend impetigo. Impetigo is a superficial skin infection seen commonly in children ages two to five years. It can occur on previously normal skin (primary) or after an abrasion or bug bite (secondary). The picture seen above is non-bullous impetigo which starts as small inflamed papules that break down leading to the honey-crusted exudate. These lesions evolve over a week and are localized. The main pathogen is Staphylococcus aureus. Beta-hemolytic streptococci (mostly group A, but sometimes C and G) are sometimes implicated as well – often along with S. aureus.

Bullous impetigo is also seen in young children commonly, and instead of the crusting, the papules enlarge, and form bull that rupture, leaving a thin brown crust behind. see the images below for a before and after look at those bullae. Bullous impetigo is caused by specific strains of Staph aureus that make exfoliative toxin A that compromises cell adhesion.

Bullous impetigo – By US Gov – http://phil.cdc.gov/phil/home.asp ID#: 5154 US Department of Health and Human Services, Public Domain, https://commons.wikimedia.org/w/index.php?curid=847758
Bullous impetigo – By Littlekidsdoc – Own work, CC BY-SA 4.0, https://commons.wikimedia.org/w/index.php?curid=64793949

Ecthyma is also a type of impetigo and causes those “punched out” lesions that are covered by the honey-crust. It is caused by Group A strep.

Diagnosis and Treatment

Impetigo is a clinical diagnosis, though if you are concerned about MRSA or recurrent cases gram satin and culture can be helpful. And the patient’s father is right – his child does need antibiotics. In general topical therapy is sufficient. Mupirocin is the first line choice here – and it is applied to the affected area three times a day for five days. Over the counter agents are generally less effective, since there is resistance out there – bacitracin-neomycin-polymyxin B (bacitracin) and neomycin aren’t recommended. Some topical quinolone were recently approved – but I haven’t sed them as there is not enough evidence supporting their use. Mupirocin works just fine.

If patients have very extensive disease you could elect to go oral. You need to cover both staph and strep spp. Options include cephalexin, doxycycline, and if you are worried about MRSA consider doxy, trimethoprim-sufamethoxazole, or clindamycin.

And finally, it is possible to get post strep glomerulonephritis following impetigo. That might show up on the boards…

References

Bowen et al. The Global Epidemiology of Impetigo: A Systematic Review of the Population Prevalence of Impetigo and Pyoderma. PLoS One 2015; 10:e0136789.

Dollani et al. Impetigo/Staphylococcal Scalded Skin Disease. Pediatrics in Review April 2020,  41 (4) 210-212; DOI: https://doi.org/10.1542/pir.2018-0206.