**Core Concept**
Erythema infectiosum, also known as fifth disease, is a viral illness caused by parvovirus B19. It typically affects children and is characterized by a distinctive "slapped-cheek" rash, fever, and mild respiratory symptoms. The disease can lead to various complications, especially in vulnerable populations.

**Why the Correct Answer is Right**
One of the complications of erythema infectiosum is aplastic crisis, which occurs when parvovirus B19 infects red blood cell precursors in the bone marrow, leading to a temporary halt in red blood cell production. This is particularly concerning in patients with sickle cell disease or other hemoglobinopathies, as it can lead to severe anemia. Another complication is arthritis, which can occur in some cases, especially in adults. However, other options may not be as directly related to the typical complications of erythema infectiosum.

**Why Each Wrong Option is Incorrect**
**Option A:** Aplastic crisis is a known complication of erythema infectiosum, making this option incorrect.
**Option B:** Arthritis can occur in some cases of erythema infectiosum, especially in adults, so this option is also incorrect.
**Option D:** While erythema infectiosum can lead to mild respiratory symptoms, pneumonia is not a typical complication of the disease, making this option the most likely correct answer.

**Clinical Pearl / High-Yield Fact**
Erythema infectiosum is often diagnosed clinically, based on the characteristic rash and mild symptoms. However, in patients with underlying hemoglobinopathies, a diagnosis of erythema infectiosum can be critical to prevent severe anemia.

**Correct Answer:** D.