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 2,124individuals, aged six to 64 years, representative by age, sex and area inMedellín, Colombia, 2009. Biological and socioeconomic variables wereanalyzed 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 IgGantibodies against the rubella virus was detected using a high sensitivity(AxSYM^®Rubella IgG – Abbott Laboratories) and a highspecificity test (VIDAS RUB IgG II^®– BioMerieux Laboratories).Proportions and weighted averages derived from a complex sample, including acorrection factor for differences in gender participation, were estimated.Association with protection for groups of biological and social variablesaccording to birth cohort was analyzed using a logistic regressionmodel.

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%CI54.4;72.8; p = 0.000) the introduction of mass immunization. The proportionof protection increased from 88.9% in those born 1990-1994, to 89.2% inthose 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 bornbefore the introduction of the immunization, seroprotection was associatedwith previous contact with cases (OR 2.6; 95%CI 1.1;5.9), self- perceivedhealth status (OR 2.5; 95%CI 1.05;6.0), educational level (OR 0.2; 95%CI0.08;0.8) and years of residence in the neighborhood (RD 0,96; 95%CI0.98;1.0) after adjusting for all variables. In those born after, serumprotection 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, withhigher titers of IgG antibodies in those born before the start of theimmunization. It is recommended that the level of long-term protection bemonitored and concerted action taken to improve potentially associatedsocioeconomic conditions.