Diagnosis is based mainly on the appearance of the skin lesion.
A culture of the skin or lesion usually grows the bacteria streptococcus or staphylococcus. The culture can help determine if MRSA is the cause, because specific antibiotics are used to treat this infection.
Cole C, Gazewood J. Diagnosis and treatment of impetigo. Am Fam Physician. 2007;75:859:864.