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Current Trends Rubella and Congenital Rubella Syndrome -- United States, 1984-1985

RUBELLA

In 1985, a provisional total of 604 cases of rubella (0.25 cases/100,000 population) was reported in the United States. This is the lowest annual total since rubella became a nationally notifiable disease in 1966; it represents a 20% decrease from the 1984 total of 752 cases and a 99% decline from 1969, the year of rubella vaccine licensure and the year with the greatest number of cases (57,686) ever reported (Figure 1).

Provisionally, in 1985, 14 states and the District of Columbia reported no rubella cases, compared with 12 states and the District of Columbia in 1984 and 14 reporting areas in 1983. Age and county data are not yet available for 1985. However, the number of counties reporting rubella declined from 284 (9%) in 1983 to 219 (7%) in 1984.

Comparison of national data for 1982-1984 indicates that the reported age-specific incidence of rubella declined for virtually all age groups during the past 3 years (Table 1). Children under 5 years of age continued to have the highest overall incidence (1.4 cases/100,000 population) and accounted for one-third of all patients for whom age was reported. Incidence declined by 49% among persons under 15 years old between 1982 and 1984, and by 25% from 1983 to 1984. The incidence for persons 15 years of age or older, who accounted for 48% of cases in 1984, declined by 75% between 1982 and 1984 and by 17% between 1983 and 1984 as a result of continued efforts to identify and vaccinate susceptible persons of childbearing age, particularly postpubertal females.

Long-term data on the occurrence of rubella among specific age groups are available from Illinois, Massachusetts, and New York City (Table 2). In the 3-year period before vaccine licensure, children had the highest occurrence of rubella, with the highest incidence rate among those 5-9 years of age. Children under 10 years of age accounted for 60% of cases, while 23% of the total cases was reported among persons 15 years of age or older. Although incidence rates declined for all age groups during 1975-1977, the greatest decreases occurred among persons under 15 years of age. The highest incidence rates were then reported among 15- to 19-year-olds, rather than 5- to 9-year-olds. Children under 10 years of age accounted for 24% of cases, while persons 15 years of age or older made up 62% of cases. Among persons 15 years of age or older, incidence rates were more than tenfold higher among 15- to 19-year-olds than among persons 20 years of age or older. More recently (1982-1984), reported incidence rates have declined by approximately 90% or more for all age groups, with the greatest decreases occurring among persons 15-19 years of age. Persons 15 years of age or older still accounted for the majority (52%) of cases but experienced a greater than 90% reduction in their risk of acquiring rubella relative to prevaccine years. The differences observed earlier in attack rates within this age group are no longer evident. CONGENITAL RUBELLA SYNDROME

Data on cases of congenital rubella syndrome (CRS) are available from reports submitted weekly to MMWR and from the National Congenital Rubella Syndrome Register (NCRSR) maintained at the Division of Immunization, Center for Prevention Services, CDC. The MMWR CRS reports are case counts with no accompanying data and are tabulated by year of report. NCRSR data are obtained through reports from state and local health departments that contain clinical and laboratory information. The NCRSR monitors reports by year of birth, with cases classified into six categories, the most specific of which, for clinical CRS cases, are "confirmed"* and "compatible"** (Table 3). Since the NCRSR cases are classified by year of birth, data are considered provisional for any given year and are subject to updating because of delayed reporting. This summary updates previous reports on surveillance of CRS in the United States.

Recent declines in CRS rates recorded by NCRSR parallel the decline in overall rubella incidence and, more specifically, in the incidence for persons 15 years of age or older (Figure 1). During 1979-1984, the reported rubella rate among persons in this age group declined 96%, from 4.8 cases/100,000 population to 0.2/100,000. Similarly, 57 confirmed and compatible CRS cases occurred in 1979 and that only two such cases occurred in 1984 (a 96% decline) (Table 4). The number of reported CRS cases declined by 71% from 1983 (seven cases) to 1984 (two cases).S Two CRS patients born in 1985 have been reported to date. Neither 1985 case was reported until 1986; one CRS patient was diagnosed within the first month of life; the second was not recognized until 8 months of age. Reported by Surveillance, Investigations, and Research Br, Div of Immunization, Center for Prevention Svcs, CDC.

Editorial Note

Editorial Note:The primary goal of rubella vaccination programs is to prevent congenital rubella infection (CRI).P When rubella vaccine was licensed in 1969, the United States adopted a policy of universal immunization of children. The focus of this rubella vaccination strategy was to control rubella in preschool-aged and young school-aged children, the primary reservoirs for rubella transmission. Such a strategy was designed to reduce and even interrupt circulation of the virus, thereby reducing the risk of exposure of susceptible pregnant women, as well as protecting children immediately and subsequently through their childbearing years (1). Accordingly, the primary target group for vaccine was children of both sexes. However, secondary emphasis was placed on also vaccinating susceptible adolescents and adults, especially women. By 1977, vaccination of children 12 months of age and older had resulted in marked declines in reported rubella incidence among children and had interrupted the characteristic 6- to 9-year rubella epidemic cycle; however, this strategy had a minimal effect on rubella incidence among persons 15 years of age and older (Figure 1). In addition, after some initial decreases, reported incidence rates of CRS stabilized (Table 4). Serologic studies of various postpubertal populations in the late 1970s and early 1980s showed that 10%-20% of persons still lacked serologic evidence of immunity to rubella (2).

By 1977, it became clear that the reason for the continued occurrence of rubella among young adults and of CRS was a failure to vaccinate persons at risk. There was no evidence of vaccine failure due to waning vaccine-induced immunity. This potential for continuing rubella transmission among populations of susceptible adults has subsequently been demonstrated by outbreaks among military recruits (3), hospital personnel (4), office workers (5-7), college students (8), and prison inmates and staff (9). Beginning in 1977 with the National Childhood Immunization Initiative, and later in conjunction with the Measles Elimination Program, efforts were intensified to vaccinate all children and susceptible postpubertal females. The number of doses of rubella vaccine administered in the public sector to persons 15 years of age or older more than doubled between 1978 and 1984 (10). Among persons 20 years of age or older, an eightfold increase occurred.

The success of these initiatives is now apparent. During 1979-1984, the reported incidence rates of CRS and of rubella among persons 15 years of age or older declined, in parallel, by 96% to all-time low levels. Meanwhile, incidence rates of rubella among children under 15 years of age have continued to decrease. As the highly immune cohorts of young children enter childbearing age, CRS can be expected to disappear from this country.

The present situation, however, is still cause for concern. In 1984, 48% of reported rubella cases occurred among persons 15 years of age or older. Furthermore, there is as yet no evidence from serologic studies that rates of susceptibility to rubella in adults have declined appreciably from prevaccine years (11). These data provide evidence that the continued occurrence of rubella in the childbearing-aged population will mean that potentially preventable CRS cases will continue to occur during the next 10-30 years. These concerns led CDC to announce an initiative in February 1985 to hasten elimination of rubella and CRS by increasing efforts to effectively vaccinate the susceptible childbearing-aged population (12).

Even though reported CRS is now at record low levels in the United States, the reported figure is believed to be an underestimation of the actual total. CDC estimates of CRS incidence rates are derived primarily from the NCRSR reporting system, a passive reporting system. Passive surveillance by its nature results in underreporting of actual disease incidence, and results in selective reporting of infants with severe and obvious CRS (e.g., cardiac or eye defects) that are recognized and reported early in life, while those with mild CRS (e.g., mental or auditory defects) are often not reported until later in life, if at all. As an example of these problems, both reported CRS patients born in 1985 were not reported until 1986, and one of the infants with cataracts and microcephaly was not diagnosed as having CRS until he was referred to a tertiary-care center at 8

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