Seroprevalence of rubella in Colombia: a birth-year cohort analysis

OBJECTIVE: To estimate the seroprevalence of rubella and associated factors. METHODS: Population-based seroprevalence study in a random sample of 2,124 individuals, aged six to 64 years, representative by age, sex and area in Medellín, Colombia, 2009. Biological and socioeconomic variables were analyzed for their association with serum protection against rubella, according to birth-year cohort; those born before (1954-1990) and after (1991-2003) the introduction of universal immunization. Titer of IgG antibodies against the rubella virus was detected using a high sensitivity (AxSYM(®)Rubella IgG – Abbott Laboratories) and a high specificity test (VIDAS RUB IgG II(®)– BioMerieux Laboratories). Proportions and weighted averages derived from a complex sample, including a correction factor for differences in gender participation, were estimated. Association with protection for groups of biological and social variables according to birth cohort was analyzed using a logistic regression model. RESULTS: Titers of IgG antibodies were higher in those born before (mean 110 UI/ml, 95%CI 100.5;120.2) compared to those born after (mean 64 UI/ml; 95%CI 54.4;72.8; p = 0.000) the introduction of mass immunization. The proportion of protection increased from 88.9% in those born 1990-1994, to 89.2% in those born 1995-1999 and to 92.1% in those born between 2000 and 2003, possibly due to boosters being administered from 1998 onwards. In those born before the introduction of the immunization, seroprotection was associated with previous contact with cases (OR 2.6; 95%CI 1.1;5.9), self- perceived health status (OR 2.5; 95%CI 1.05;6.0), educational level (OR 0.2; 95%CI 0.08;0.8) and years of residence in the neighborhood (RD 0,96; 95%CI 0.98;1.0) after adjusting for all variables. In those born after, serum protection was associated with effective sleep time (OR 1,4; 95%CI 1.09;1.8) and self-perceived health status (OR 5.5; 95%CI 1.2;23.8). CONCLUSIONS: The seroprevalence profile changed with the mass immunization plan, with higher titers of IgG antibodies in those born before the start of the immunization. It is recommended that the level of long-term protection be monitored and concerted action taken to improve potentially associated socioeconomic conditions.