Current Trends Rubella and Congenital Rubella Syndrome -- United States, 1985-1988

RUBELLA

A provisional total of 221 cases of rubella was reported in the United States in 1988 (0.1 cases per 100,000 population), the lowest since rubella became a nationally notifiable disease in 1966. In 1987, 306 cases of rubella (0.1/100,000) were reported. The incidence of rubella has declined by more than 99% since 1969, the year rubella vaccine was licensed (Figure 1).

In 1987, the last year for which complete data are available, 20 of 52 reporting areas (which comprise the 50 states, District of Columbia, and New York City (NYC)) reported no rubella cases, compared with 18 reporting areas in 1986 and 14 in 1985. One hundred five (3.3%) counties reported rubella cases in 1987, compared with 152 (4.8%) in 1985. The reported age-specific incidence rates of rubella declined for all age groups during these 3 years (Table 1). In 1987, children less than 5 years of age continued to have the highest incidence rate (0.5 cases/100,000 population) and accounted for 28% of the total number of patients with known ages. The rate for persons greater than or equal to15 years of age, who accounted for 49% of the patients with known ages in 1987, declined most dramatically--by 59% (0.19/100,000 in 1985 to 0.08/100,000 in 1987).

Long-term trends of rubella incidence among specific age groups can be assessed by comparing recent data from the total United States with those from three areas for which age-specific data were available before 1975--Illinois, Massachusetts, and NYC (Table 2). In the 3-year period before vaccine licensure (1966-1968), the estimated risk of acquiring rubella was highest in children 5-9 years of age. Of the patients with known ages, children less than 10 years of age accounted for 60%, while only 23% of the total was reported among those greater than or equal to15 years of age. By comparison, the reported incidence rates for 1985-1987 have declined by greater than or equal to95% for all age groups, with the greatest decreases occurring among persons less than 20 years of age. Persons aged greater than or equal to20 years accounted for just over half of all patients with known ages. Although the decrease in incidence rates was smallest for this age group, their risk of acquiring rubella still declined more than 95%, relative to prevaccine licensure years. CONGENITAL RUBELLA SYNDROME

Data on congenital rubella syndrome (CRS) are available from reports submitted weekly to the MMWR and from the National Congenital Rubella Syndrome Registry (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. 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 patient's birth and are classified into six clinical categories (1), the most specific of which are "CRS-confirmed" (i.e., cases with both congenital anomalies and laboratory evidence of rubella infection) and "CRS- compatible" (i.e., cases that satisfy selected clinical criteria without laboratory confirmation). Beginning in 1984, information was routinely collected to evaluate whether a CRS case was "indigenous" or "imported."* Since the NCRSR cases are classified by year of patient's birth, data are considered provisional for any given year; delays in diagnosis and/or reporting may result in the updating of figures. This summary updates previous reports on surveillance of CRS in the United States (1).

For infants born in 1987, six CRS cases were reported to the NCRSR, of which three were considered indigenous. All three were confirmed CRS cases, and one of them occurred in a mother who had had at least one previous pregnancy. Only one CRS case has been reported thus far for 1988. Recent declines in rates of CRS recorded by NCRSR have paralleled the decline in overall rubella incidence and, more specifically, in the incidence for persons greater than or equal to15 years of age (Figure 1). During 1970-1987, the reported rate of rubella among persons in this age group declined 97%, from 2.3 to 0.1 cases/100,000 population. In 1970, 67 CRS cases occurred (1.80/100,000 live births), and three have been reported as of March 22, 1989, for 1987 (0.08/100,000 live births), representing a 96% decline (Table 3). This downward trend was interrupted in 1986, when 12 CRS cases were reported (2). In that year, eight of these cases were reported to the NYC Department of Health 8-10 months after the peak of a rubella outbreak in NYC (3). Reported by: Surveillance, Investigations, and Research Br, Div of Immunization, Center for Prevention Svcs, CDC.

Editorial Note

Editorial Note: As part of the 1990 health objectives for the nation, the Public Health Service set a goal to reduce the number of rubella cases to less than 1000 and to reduce CRS to less than 10 cases annually (4). The former goal was achieved for the first time in 1983, when 970 rubella cases were reported (5). Although the goal for CRS has also been reached, unacceptable morbidity is still occurring. The primary aim of rubella vaccination programs is to prevent congenital rubella infection, which can result in miscarriages, abortions, stillbirths, and CRS in infants. When rubella vaccine was licensed in 1969, the United States adopted a policy of universal immunization of children of both sexes. The focus of this rubella vaccination strategy was to control rubella in preschool-aged and young school-aged children, the primary sources of rubella transmission. This strategy was designed primarily to reduce and interrupt circulation of the virus, thereby reducing the risk of exposure to susceptible pregnant women. Also, vaccinated children would be protected immediately, and their immunity was expected to persist at least through their childbearing years (6). Secondary emphasis was placed on vaccinating susceptible adolescents and adults, especially women.

The success of the rubella control program is apparent. In 1966-1987, the reported incidence rates of CRS and of rubella among persons greater than or equal to15 years of age declined in parallel by 95%-96% to all-time low levels. Meanwhile, incidence rates of rubella in children less than 15 years of age have continued their downward trend. As the highly im- mune cohorts of young children enter the childbearing years, CRS should disappear from this country.

However, concern continues despite the dramatic success of the U.S. rubella immunization program. In 1987, 48% of reported rubella cases were in persons greater than or equal to15 years of age (32% of all cases were in persons 15-29 years of age). Most serologic surveys of various postpubertal populations carried out during the 1970s and early 1980s found rates of rubella susceptibility comparable to the prevaccine years: 10%-20% of persons still lacked serologic evidence of immunity to rubella (7-9). Updated population-based serologic surveys are needed to fully characterize the magnitude and extent of risk for this adolescent and young adult population. The NYC experience during 1985-1986 (2,3) and several recent college outbreaks (10) highlight the possible risk of disease in postpubertal women. The continued occurrence of rubella in childbearing-aged populations suggests that potentially preventable cases of CRS may continue to occur during the next 10-30 years. Such concerns led CDC to announce an initiative in February 1985 to hasten elimination of rubella and CRS by targeting susceptible childbearing-aged populations for vaccination (11).

In addition, the reported figure for CRS cases is believed to underestimate the actual total, perhaps capturing only 10% of the actual total (12). The NCRSR is a passive reporting system that, by its nature, results in underreporting of actual disease incidence and selective reporting of infants with severe and obvious CRS recognized and reported early in life. The limitations of current CRS surveillance underscore the need for all specialists who treat children with congenital anomalies compatible with CRS to continue to consider it in the differential diagnosis and to report all suspected cases to their state health departments.

As with other adult immunizations, creative approaches are necessary to enhance rubella immunization levels in the childbearing-aged population. Adopting and enforcing comprehensive kindergarten through 12th grade school immunization laws (especially for postpubertal elementary and secondary school students) and requiring proof of immunity to rubella as a condition for college entry can minimize the risk of rubella outbreaks in these populations (13). Another way to reach susceptible postpubertal women is to offer rubella vaccine at any encounter with the health-care system. After excluding patients who say they may be pregnant and counseling about the advisability to avoid conception for 3 months after vaccination, practitioners should not hesitate to vaccinate childbearing-aged women against rubella. No CRS-like defects have been detected in 212 infants born to susceptible mothers inadvertently vaccinated with RA27/3 live rubella virus vaccine during pregnancy (14;CDC, unpublished data). NCRSR surveillance data indicate that one third to one half of mothers delivering CRS infants had had a previous live birth, suggesting that both postpartum vaccination and use of rubella vaccine in family-planning clinics could have an important impact on the overall occurrence of reported CRS. Physicians and other health-care personnel should offer rubella vaccine whenever they encounter a potentially susceptible woman lacking contraindications for vaccination. Susceptible persons identified through preemployment, premarital, or prenatal screening should be offered vaccine at follow-up visits.

References

1. CDC. Rubella and congenital rubella--United States, 1984-1986. MMWR 1987;36: 664-6,671-5. 2.CDC. Rubella and congenital rubella syndrome--New York City. MMWR 1986;35:770-4,779. 3.CDC. Rubella outbreak among office workers--New York City. MMWR 1985;34:455-9. 4.Public Health Service. Promoting health/preventing disease: objectives for the nation. Washington, DC: US Department of Health and Human Services, Public Health Service, 1980:22. 5.Williams NM, Preblud SR. Rubella and congenital rubella surveillance, 1983. CDC surveillance summaries, 1984. MMWR 1984;33(no. 4SS):1SS-10SS. 6.Orenstein WA, Bart KJ, Hinman AR, et al. The opportunity and obligation to eliminate rubella from the United States. JAMA 1984;251:1988-94. 7.Crowder M, Higgins HL Jr, Frost JJ. Rubella susceptibility in young women of rural east Texas: 1980 and 1985. Tex Med 1987;83:43-7. 8.Witte JJ, Karchmer AW, Case G, et al. Epidemiology of rubella. Am J Dis Child 1969; 118:107-11. 9.Bart KJ, Orenstein WA, Preblud SR, Hinman AR. Universal immunization to interrupt rubella. Rev Infect Dis 1985;7(suppl 1):S177-84. 10.CDC. Rubella in colleges--United States, 1983-1984. MMWR 1985;34:228-31. 11.CDC. Elimination of rubella and congenital rubella syndrome--United States. MMWR 1985;34:65-6. 12.Cochi SL, Edmonds LE, Dyer K, et al. Congenital rubella syndrome in the United States, 1970-1985: on the verge of elimination. Am J Epidemiol 1989;129:349-61. 13.CDC. Immunization practices in colleges--United States. MMWR 1987;36:209-12. 14.CDC. Rubella vaccination during pregnancy--United States, 1971-1986. MMWR 1987; 36:457-61. *Based on definitions approved by the Council of State and Territorial Epidemiologists, an imported case of CRS is defined as CRS in a U.S. or non-U.S. citizen whose mother was outside the United States during her presumed exposure to rubella. If the timing of exposure to rubella cannot be determined, the mother must have been outside the United States throughout the 21 days before conception and the first 20 weeks of her pregnancy.

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