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(Berkow, 1987; Schlossberg and Topolsky, 1977), serious complications are few and rare. Encephalitis, occasionally resulting in death, and thrombocytopenia have been reported (Morse et al., 1966; Sherman et al., 1965), as have chronic arthralgia, arthritis, and polyneuritis (Ogra and Herd, 1971; Ogra et al., 1975; Schaffner et al., 1974). The latter vary in frequency with age and sex, being greatest in adult females and least in prepubertal children. Complications of congenital rubella are numerous and profound (see the section Clinical Description). A rare late syndrome of congenital rubella is rubella panencephalitis (Townsend et al., 1975; Weil et al., 1975).

Descriptive Epidemiology

Ecology of the Rubella Virus Rubella virus is spread by airborne droplet nuclei or by close contact. Rubella does not appear to be as contagious as certain other common viral childhood diseases are, as indicated by seroepidemiologic studies showing that even after explosive outbreaks, 10 to 20 percent of young adults may remain susceptible (Plotkin, 1988). However, under crowded conditions where the proportion of susceptible individuals is high, rubella can be highly infective (Brody, 1966; Grayston et al., 1972; Halstead et al., 1969). Exposure to rubella disease is believed to confer life-long immunity (Berkow, 1987).

Humans are the sole host of the rubella virus, and subclinical cases are common. Virus has been shown to be present in nasopharyngeal secretions from 7 days before to 14 days after onset of the rash in postnatal cases. Infants with congenital rubella can shed the virus in nasopharyngeal secretions and urine for a year or more after birth (Cooper et al., 1965; Scheie et al., 1967).

Distribution by Person Age at the time of infection varies geographically for postnatal rubella. In areas where living conditions are crowded, rubella tends to occur at an early age; in areas that are less crowded or that are isolated, such as island nations, rubella tends to occur at a later age, with a significant number of people remaining seronegative into young adulthood (Ingalls, 1967). Congenital rubella affects more infants of younger mothers than infants of older mothers, perhaps because the former are more likely to be seronegative (Plotkin, 1988).

Distribution by Place Rubella occurs worldwide (Assaad and LjungarsEsteves, 1985; Cockburn, 1969). The disease is probably more common in areas where living conditions are crowded, although accurate incidence rates are difficult to obtain in the absence of seroepidemiologic confirmation, because many childhood cases are asymptomatic and therefore go undetected (Plotkin, 1988).