A 7-year-old child develops malaise, cough, coryza, and conjunctivitis with a high fever. Prior to this illness he was completely healthy. Further questioning reveals that he has not received any childhood vaccinations because of his parents' religious beliefs. Examination of his mouth reveals blue white spots on a red base beside his second molars. The next day he develops an erythematous, nonpruritic, maculopapular rash at his hairline and behind his ears, which spreads over his body. Which of the following is the most likely diagnosis?

This is a typical case of measles. The Koplik spots in the mouth are easily missed with poor illumination. They are white-blue spots of 1 mm on a red background and are not seen in any other infectious disease. The rash of measles becomes confluent while that of rubella does not. Pneumonia is an infrequent complication but accounts for many measles deaths. Giant cell pneumonia is also seen, most commonly in children suffering with a severe disease such as leukemia or immunodeficiency. Treatment for most patients is supportive care. The other potentially lethal complication of measles is encephalitis. The Koplick spots help differentiate this illness from rubella, and the distribution of the rash rules out infection from coxsackievirus.