Seroprevalence of mumps in an epidemic period in Medellín, Colombia.

OBJECTIVE

We related seroprevalence and outbreaks data in order to identify factors that could explain the occurrence of outbreaks despite high vaccination coverage in Medellín Colombia.

METHODS

Samples from a population seroprevalence data obtained in 2009 in a random survey were analyzed. IgG levels were determined for mumps using 2 commercial tests of 2119 individuals aged 6-64 years. A comparative analysis was undertaken using age-specific mumps seroprevalence data and information of 98 epidemiological investigations of mumps outbreaks reported in 2009.

RESULTS

Overall, seroprevalence was 91.6% (95% CI=89.3-93.5%). The age-specific seronegativity was 20.3% and 20.6% in age groups 11-15 years and 16-20 years respectively. Individuals aged 6-20 years were the most affected during outbreaks. In individuals born in 2003, a year after the change in the booster schedule from 10 to 5 years, the proportion of unvaccinated individuals (14%) and those who received only one dose of MMR (45%) increased substantially. On average, 23.5 days elapsed between the onset of symptoms in secondary cases and the outbreak investigation.

CONCLUSION

Potential contributing factors for the occurrence of outbreaks of mumps were the relatively high prevalence of seronegativity among individuals aged 11-20 years, delays in investigation and control of outbreaks, and incomplete vaccination schedules.