Current Trends Rubella and Congenital Rubella -- United States, 1983

RUBELLA

A provisional total of 954 cases of rubella was reported in 1983--the lowest since rubella became a notifiable disease in 1966. The greatest number of cases ever reported was 57,686 in 1969. 1983 cases decreased by 59% from 1982 (2,325 cases) and by 66% from the 3-year average annual total for 1980-1982. Fourteen states and the District of Columbia reported no cases in 1983; seven were free of rubella in 1982. California (292 cases), Texas (116), New York City (87), and Florida (71) accounted for 59% of all 1983 cases. California alone accounted for 31% of the 1983 cases but experienced a 79% decrease from 1982, when it accounted for 62% of all U.S. cases. Age-specific data are not yet available. CONGENITAL RUBELLA SYNDROME

While data on rubella are available only through CDC's surveillance system (reported weekly in MMWR's Tables I and III), data on congenital rubella syndrome (CRS) cases for 1983 are available from reports submitted weekly to MMWR and from the National Congenital Rubella Syndrome Registry (NCRSR) maintained at CDC's Division of Immunization.* The MMWR CRS reports are case counts with no accompanying data and are tabulated by year of report. The NCRSR monitors reports by year of birth that contain information allowing classification into six categories, the most specific for clinical CRS cases being "confirmed" and "compatible" (C&C) (Table 1). Since the NCRSR cases are classified by year of birth, data are considered provisional for any given year and are subject to frequent updating because of delayed reporting.

In contrast to the reported 59% decrease in rubella from 1982 to 1983, reported CRS increased almost threefold--from seven cases in 1982 to 20 cases in 1983 (Table 2). However, only seven (35%) of these 20 infants were born in 1983 (Table 3). Seventeen of these have been classified by NCRSR criteria (the other three were born in 1982). Fourteen (82%) of the 17 cases were either confirmed or compatible, including four of the seven infants born in 1983.

The NCRSR includes two additional confirmed cases in infants born in 1982 but not yet reported in MMWR. Thus, in contrast to the MMWR data, the updated NCRSR C&C totals currently demonstrate a 64% decrease between 1982 (11 cases) and 1983 (4) (Table 2).

The 20 infants with CRS reported in MMWR in 1983 were from California (12 cases), New York (2), Arkansas (1), Illinois (1), Kansas (1), Oregon (1), South Dakota (1), and Wisconsin (1). Three of the California infants (all C&C) were born in 1983; eight (six C&C), in 1982; and one (C&C), in 1981. California now accounts for 64% (7/11) of C&C cases for 1982 and 75% (3/4) of C&C cases for 1983. These data are consistent with the observed increase in reported rubella activity in childbearing-age populations that occurred in California in 1982 (1).

Since the 1983 data reported in MMWR indicate that one-half the infants were born in the previous year, the increase in CRS reporting occurred among 1982 births and parallels the twofold increase in the rubella rate among persons 15 years of age and older reported between 1981 (0.4 cases/100,000 population) and 1982 (0.8 cases/100,000 population). Reports of CRS to both MMWR and NCRSR have declined markedly as overall rubella and rubella in postpubertal populations have reached all-time lows (Table 2). After some initial decreases in the years following the licensure of rubella vaccine, CRS rates stabilized, with only minimal differences between MMWR and NCRSR reports. The increase in incidence in 1979 in both systems reflects the outcome of outbreaks of rubella in 1977-1978. Since 1981, the reported rates in both systems have been lower than 0.6 cases/100,000 live births and have reached record low levels.

The recent declines in CRS rates recorded by the NCRSR parallel the decline in the overall rubella rate and, more specifically, in the rate for persons 15 years of age or older (Figure 1). Between 1979 and 1982, the reported rate of rubella among persons in this group declined from 4.8 cases/100,000 population to 0.8/100,000 (an 83% decline). Similarly, 57 C&C cases were reported in 1979, but only 11 in 1982 (an 83% decline) (Table 2). Based on 1983 C&C data, cases have declined by 93% since 1979. Reported by Div of Immunization, Center for Prevention Svcs, CDC.

Editorial Note

Editorial Note: Although reported rubella rates are at an all-time low, the potential for increased rubella activity in older individuals, particularly women of childbearing age, still exists. The rubella susceptibility rate for adolescents and young adults remains at levels of 10%-20% (2). This potential for an increase in rubella was demonstrated when outbreaks in postpubertal populations in universities, hospitals, and other places of employment resulted in a 12% increase in reporting of rubella between 1981 (which had been a previous record low year) and 1982 (1).

The large number of rubella and CRS cases in California may be related to the high rubella susceptibility rate among its postpubertal population (3,4) and potentially to better disease surveillance. Recent serosurveys of California's adolescent and adult populations have documented a decline in the susceptibility from the prevaccine period, although the susceptibility rate is still higher than that in other states (2,5). One response to this situation was the revision of the state's immunization law in 1982 to ensure that all students from kindergarten to 10th grade, especially postpubertal girls, provide proof of rubella vaccination. Rubella and CRS rates are declining in California as well as in the rest of the country. The increased focus on vaccinating postpubertal school-aged children in California and other states should speed that decline.

The most important indicator of the success of rubella immunization programs is the decrease in reported occurrence of congenital rubella infection.** CRS represents the most serious outcome in terms of health burden. Costs for the lifetime care of an infant with CRS have recently been estimated to be in excess of $200,000 (6).

CDC estimates of CRS rates are derived primarily from the MMWR and NCRSR reporting systems, both of which are passive. Passive surveillance results in underreporting of actual disease incidence. One indication of underreporting is the early age at which CRS infants reported to CDC are diagnosed. Of all the 379 NCRSR C&C infants for whom the age at diagnosis is known, 65% (247/379) were diagnosed within the first month of life, and only 6% (24/379) after 1 year of age. Infants with severe and obvious CRS (e.g., cardiac or eye defects) are recognized and reported early in life and are most likely to be classified C&C, while those with mild CRS (e.g., mental or auditory defects) are often reported later in life or not at all. An average of 79% of all cases reported to the NCRSR are C&C (Table 4). In contrast, the mild cases, which probably total more than one-half of all CRS cases, are not reported regularly to MMWR (7-9). Also, an analysis of the NCRSR C&C cases and the Birth Defects Monitoring Program C&C cases, using a capture-recapture statistical model, suggests that only one-fifth of all C&C cases are reported to NCRSR (10). Thus, approximately one-tenth (1/2 x 1/5) of all CRS cases are probably reported through the NCRSR (10).

In spite of underreporting, the CDC data are useful for monitoring trends. The fact that the reported CRS rate has paralleled reported rubella in postpubertal populations based on data for the 15-year-or-older age group suggests that the decline in CRS between 1979 and 1983 is real.

The differences between MMWR and NCRSR reports for 1983 are explained by the differences in classifying CRS infants by year of report versus year of birth. Data are not available to compare the two systems for previous years; however, the trends appear to be similar, considering the 1-year lag for MMWR cases.

An infant with CRS is only one outcome of infection in a pregnant woman. Therapeutic abortion is another serious consequence. Outbreak investigations in the United States suggest that therapeutic abortion is considerably more common than CRS (11). Data from the United Kingdom indicate that the number of abortions in England and Wales from 1976-1978 was more than 10 times the number of CRS cases reported for all of the United Kingdom (12,13). To further assess the impact of congenital rubella infection in the United States, it will be important to follow infected pregnant females to determine the outcomes of pregnancy.

The available data indicate that CRS is now at or close to record low levels. However, given the underreporting, there is still a substantial health burden in the United States that can be avoided (14). In the absence of intensified efforts, it will take 10-30 years before the immune cohort of vaccinated schoolchildren will comprise the childbearing-age group. At that time, CRS may disappear from this country. The elimination of CRS can be hastened but requires intensified efforts to vaccinate older, susceptible school-aged children and females of childbearing age. To accomplish this in a cost-efficient manner, cooperation between the private and public sectors will be needed to delineate risk factors that would allow

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