**Core Concept**
Impetigo is a highly contagious superficial skin infection caused by Staphylococcus aureus or Streptococcus pyogenes. It typically affects children and is characterized by red sores that burst and form a yellow crust.

**Why the Correct Answer is Right**
Impetigo is indeed a highly contagious bacterial infection. The bacteria produce exotoxins that cause the skin to become red, inflamed, and eventually form a yellowish crust. The crust is composed of bacteria, dead skin cells, and other debris. The infection can spread through direct contact with an infected person or through contaminated items such as toys, clothing, or bedding.

**Why Each Wrong Option is Incorrect**
**Option A:** This option is incorrect because impetigo is not caused by a viral infection, but rather by bacterial pathogens.
**Option B:** This option is incorrect because while impetigo can be treated with antibiotics, it is not a fungal infection.
**Option C:** This option is incorrect because impetigo is not typically associated with a severe systemic infection, but rather a localized skin infection.

**Clinical Pearl / High-Yield Fact**
To diagnose impetigo, look for characteristic red sores that burst and form a yellow crust. Impetigo can be spread through direct contact with an infected person or contaminated items, making it essential to practice good hygiene, such as washing hands frequently and avoiding sharing personal items.

**Correct Answer: A. Impetigo is caused by a viral infection.**