Epidemiologic Notes and Reports Rubella and Congenital Rubella -- United States, 1984-1986 Rubella

In 1986, 551 cases of rubella (0.23 cases/100,000 population) were reported in the United States. The incidence of rubella declined by 12% from the 1985 total (630) and has declined by 99% since 1969, the year of rubella vaccine licensure. The current total is the lowest since rubella became a nationally notifiable disease in 1966 (Figure 1).

In 1986, 18 of 52 reporting areas (50 states, the District of Columbia, and New York City) reported no rubella cases, compared with 15 reporting areas in 1985 and 13 in 1984. One hundred sixty-one counties (5%) reported rubella cases in 1986, compared with 219 (7%) in 1984.

Comparison of national data for 1984-1986 indicates that the reported age-specific incidence rates of rubella declined for virtually all age groups during the past 3 years (Table 1). Children less than 5 years of age continued to have the highest overall incidence rate (0.8/100,000) and accounted for 28% of all patients for whom age was reported during 1986. The incidence rate for persons less than 15 years old declined by 42% between 1984 and 1986. The rate for persons greater than or equal to15 years of age, who accounted for 58% of the cases in 1986, declined by 15% between 1984 and 1986 (0.20/100,000 and 0.17/100,000, respectively).

Long-term, age-specific data on the occurrence of rubella are available only from Illinois, Massachusetts, and New York City. In the 3-year period before vaccine licensure (1966-1968), the reported risk of acquiring rubella in these three locations was highest for children 5-9 years of age (Table 2). Children less than 10 years of age accounted for 60% of the cases, while only 23% of the total reported cases were among those greater than or equal to15 years of age. During 1975-1977, although incidence rates had declined for all age groups, the greatest decreases occurred among persons less than 15 years of age. Consequently, the highest incidence rates during this period were reported among 15- to 19-year-olds rather than 5- to 9-year-olds. Children less than 10 years of age accounted for only 24% of cases, while persons greater than or equal to15 years of age made up 62% of cases. Incidence rates were more than tenfold higher for 15- to 19-year-olds than for those greater than or equal to20. More recently (1984-1986), nationally reported incidence rates have declined by 95% or more for all age groups, with the greatest decreases occurring among persons less than 20 years of age. Persons greater than or equal to15 years of age, who accounted for the majority (56%) of cases, had experienced a greater than 95% reduction in their risk of acquiring rubella, relative to prevaccine years. Differences in attack rates between 15- to 19-year-olds and those greater than 20 years of age were no longer observed. Congenital Rubella Syndrome

Data on cases of congenital rubella syndrome (CRS) are available from reports submitted weekly to the MMWR Morbidity Surveillance System and from the National Congenital Rubella Syndrome Register (NCRSR) maintained by 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. The NCRSR contains clinical and laboratory information on cases of CRS that are reported by state and local health departments. The NCRSR cases are monitored by year of birth and are classified into six clinical categories, as follows:

1. CRS CONFIRMED--Defects present and one or more of the following:

1. Rubella virus isolated.

2. Rubella-specific immunoglobulin M (IgM) present.

3. Infant's rubella IgG antibody titer persists above and beyond that expected from passive transfer of maternal antibody (i.e., infant's rubella IgG titer does not fall off at the expected rate of one twofold dilution/month). 2. CRS COMPATIBLE--Laboratory data insufficient for confirmation and any two complications listed in A or one from A and one from B:

4. Cataracts and congenital glaucoma (either or both count as one), congenital heart disease, loss of hearing, pigmentary retinopathy.

5. Purpura, splenomegaly, jaundice, microcephaly, mental retardation, meningoencephalitis, radiolucent bone disease. 3. CRS POSSIBLE--Some compatible clinical findings that do not fulfill the criteria for a compatible case. 4. CONGENITAL RUBELLA INFECTION ONLY--No defects present but laboratory evidence of infection. 5. STILLBIRTHS--Stillbirths that are thought to be secondary to maternal rubella infection. 6. NOT CRS--One or more of any of the following inconsistent laboratory findings for a child without evidence of an immunodeficiency disease:

6. Rubella antibody titer absent in a child less than or equal to24 months.

7. Rubella antibody titer absent in mother.

8. Rubella antibody titer decline in an infant consistent with the normal decline of passively transferred maternal antibody after birth. (The expected rate of decline of maternal antibodies is one twofold dilution/month.) Infants are diagnosed as having confirmed cases when both defects and laboratory evidence of rubella infection are present. Cases that satisfy only selected clinical criteria in the absence of laboratory confirmation are designated as compatible. 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 rates of CRS recorded by NCRSR have paralleled the decline in overall rubella incidence and, more specifically, the incidence for persons greater than or equal to15 years of age (Figure 1). During 1979-1986, the reported rate of rubella among persons in this age group declined 96%, from 4.8 to 0.2 cases/100,000 population. Similarly, reported data showed that 57 confirmed and compatible cases of CRS occurred in 1979 and that only two such cases occurred in 1985 (a 96% decline)* (Table 3).

Twelve cases of CRS were reported in 1986, reversing a consistent downward trend since 1982. Eight cases were reported to the New York City (NYC) Department of Health 8-10 months after the peak of a rubella outbreak in NYC (2). As of September 1987, NCRSR has received reports of two cases of CRS among children born in 1987. 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), which can result in miscarriages, abortions, stillbirths, and congenital rubella syndrome (CRS) in infants. 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- and young school-aged children, who are the primary sources of rubella transmission. This strategy was designed to reduce and even to interrupt circulation of the virus, thereby reducing the risk of exposure for susceptible pregnant women. Vaccinated children would be protected immediately, and immunity was expected to persist through their childbearing years (3). Accordingly, children of both sexes were the primary target group for vaccination.

Secondary emphasis was placed on vaccinating susceptible adolescents and adults, especially women. By 1977, vaccination of children greater than or equal to12 months of age had resulted in marked declines in reported rubella incidence in children and had interrupted the characteristic 6- to 9-year rubella epidemic cycle. However, this strategy had a minimal effect on rubella incidence in persons greater than or equal to15 years (Figure 1). Moreover, after some initial decreases, reported incidence rates of CRS stabilized (Figure 1, Table 3). Serologic surveys of various postpubertal populations carried out during the 1970s and early 1980s found rates of rubella susceptibility comparable to those of the prevaccine years: 10% to 20% of persons surveyed lacked serologic evidence of immunity to rubella (4).

Beginning in 1977, intensified efforts were initiated to vaccinate all children and susceptible postpubertal females. The number of doses of rubella vaccine distributed in the public sector to persons greater than or equal to15 years of age more than doubled between 1978 and 1986 (CDC, unpublished data). Among persons greater than or equal to20 years of age, there was a greater than 15-fold increase. In spite of the greater use of vaccine in this age group, only a small proportion of the susceptible groups have been vaccinated.

The success of the rubella control program is apparent. In the period 1979-1985, the reported incidence rates of CRS and of rubella among persons greater than or equal to15 years of age declined by approximately 96%, to all-time low levels. Because reported rubella cases are currently few in number, small year-to-year changes should be interpreted with caution. Incidence rates of rubella in children less than 15 years of age have, however, continued their downward trend. As the highly immune cohorts of young children enter the childbearing years, CRS can be expected to continue to decrease in this country.

Despite the success of the U.S. rubella immunization program,

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