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  • Title: Modelling the incidence of congenital rubella syndrome in developing countries.
    Author: Cutts FT, Vynnycky E.
    Journal: Int J Epidemiol; 1999 Dec; 28(6):1176-84. PubMed ID: 10661666.
    Abstract:
    BACKGROUND: As of 1997, less than one-third of developing countries included rubella vaccine in their national immunization programme. In countries that have achieved high coverage of measles vaccine, an ideal opportunity exists to include control of rubella and congenital rubella syndrome (CRS) in enhanced measles control activities. Data on the burden of congenital rubella syndrome are important to guide rubella vaccination policies. METHODS: We reviewed the literature to identify studies of rubella antibody prevalence in developing countries that were conducted on populations with no major selection bias, prior to wide-scale rubella vaccination in the country. We used a simple catalytic model to describe the age-specific prevalence of susceptibility to rubella virus infection in given populations. Estimates of the incidence of infection among pregnant women were calculated using expressions for the average prevalence of susceptibility to infection and the incidence of infection during gestation. To estimate the number of cases of CRS, we assumed an overall risk of 65% after infection in the first 16 weeks of pregnancy and zero risk thereafter. These estimates were derived for each country for which data were available, then for each World Health Organization region, excluding Europe. RESULTS: The estimated mean incidence of CRS per 100,000 live births was lowest in the Eastern Mediterranean region (77.4, range 0-212) and highest in the Americas (175, range 0-598). The mean of the estimates of the total number of cases of CRS in developing countries in 1996 was approximately 110,000. The range was, however, very wide, from as few as 14,000 to as many as 308,000 cases. CONCLUSIONS: Congenital rubella syndrome is an under-recognized public health problem in many developing countries. There is an urgent need for collection of appropriate data to estimate the cost-effectiveness of a potential global rubella control programme. Inclusion of rubella vaccine in the national immunization program was found to be implemented in less than one-third of the developing countries in a review conducted by WHO. This paper examines the incidence of congenital rubella syndrome (CRS) cases in developing countries using published rubella infection prevalence. Documented literature of previous studies and medical data on women attending antenatal clinics were gathered and rubella antibody prevalence was identified before the wide-scale rubella vaccination. A catalytic model was used in describing age-specific prevalence of rubella virus infection in given populations, while expressions for the average prevalence of susceptibility to infection and incidence of infection during gestation was used to estimate the incidence of infection among pregnant women. Using the data gathered from each country and WHO regions, an overall risk of 65% after infection in the first 16 weeks and zero risk of defect later in pregnancy was assumed to estimate the incidence of CRS. Results revealed that the estimated mean incidence of CRS per 100,000 live births was significantly lower in the eastern Mediterranean region (77.4, range 0-212) and higher in the Americas (175, range 0-598). On the other hand, the 1996 CRS mean estimate for developing countries was approximately 110,000, ranging from 14,000 to 308,000 cases. This study concludes with the stated need for an improved CRS program in developing countries as well as adequate data collection necessary for cost-effectiveness evaluation of potential global rubella control programs.
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