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.
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