During the early 1900s, six common childhood exanthematous infections were defined by the numbers 1 through 6. The etiologic agents of these infections were unknown. Over the next century, the etiologies of these exanthems were defined, and 4 of the 6 were demonstrated to be caused by viruses (Table 19.1). The first exanthema was caused by the measles virus, the third by the rubella virus, the second and fourth by bacterial toxins, the fifth by parvovirus, and the sixth by human herpesvirus-6 (HHV-6).

In developed countries where most children have received measles and rubella vaccinations, other viral exanthems are often confused with breakthrough measles or rubella. For example, in a study of 2299 Finnish children with exanthems thought to be measles or rubella, only 6% actually had measles or rubella. When acute and convalescent serologies were performed, other diagnoses, including parvovirus (20%), enterovirus (9%), adenovirus (4%), and human herpesvirus (4%), were defined.

This chapter discusses the classic childhood viral exanthems: measles (rubeola), German measles (rubella), and exanthem subitum (roseola). Parvovirus infection is discussed in Chapter 189, Parvovirus Infection (Acute and Chronic).

RUBEOLA

Rubeola (measles) is caused by an RNA virus with one antigenic type and is classified in the genus Morbillivirus in the Paramyxoviridae family. The licensure of both a live attenuated and killed measles vaccine in 1963 resulted in a 98% diminution in incidence rates. The killed vaccine proved problematic, and only the live vaccine has remained available since 1967.