Final answer:
The symptoms listed suggest that the 12-month-old infant may have measles, a highly contagious viral infection identified by a distinctive rash that spreads from the face to the rest of the body, accompanied by Koplik's spots, fever, and respiratory symptoms.
Step-by-step explanation:
The symptoms described in a 12-month-old infant with a fever, runny nose, cough, white spots in the mouth, followed by a rash that began on the face and now has spread to the entire body, are indicative of a communicable infection known as measles. Measles is a viral infection characterized by Koplik's spots, a high fever, cough, runny nose, and a red, macular rash that becomes confluent and spreads from the face to the rest of the body. Diagnosis is clinched by the presence of Koplik's spots, along with the characteristic rash, but it can be confirmed with serological tests. Treatment is primarily supportive, and prevention through vaccination is highly effective.
While both roseola and fifth disease can present with initial cold-like symptoms and a rash, roseola, typically caused by human herpesvirus-6, leads to a high fever and a rash that starts on the trunk and fifth disease, caused by parvovirus B19, is known for its "slapped cheek" rash on the face. It's important to distinguish measles from these conditions as measles can have more severe complications and is highly contagious. A healthcare provider should be consulted for an accurate diagnosis and proper treatment of these viral infections.