Final answer:
Fifth disease, also known as erythema infectiosum caused by parvovirus B19, produces a nonpruritic rash that resembles ringworm but fades in the center and is not fungal like ringworm.
Step-by-step explanation:
The disorder that causes a transitory truncal rash that is nonpruritic, pink with erythematous macules, and may fade in the center to appear ring-like is known as Fifth disease, also called erythema infectiosum. This disease is caused by parvovirus B19, and it is much different from the ring-shaped rash caused by the fungus Trichophyton, which leads to ringworm.
Ringworm is a common fungal infection that presents with a characteristic ring-shaped rash, but unlike Fifth disease's rash, it tends to be pruritic (itchy) and does not have the same fading in the center. Moreover, ringworm is diagnosed and confirmed by culturing in Sabouraud's agar and by its fluorescence under a Wood's lamp, contrasted with the symptoms and rash pattern for the diagnosis of Fifth disease.