Seroepidemiology of the recent mumps virus outbreaks in Ireland

BackgroundTwo recent mumps outbreaks have occurred in Ireland in 2004/2005 and 2008/2009.ObjectivesTo retrospectively investigate any potential shifts in the gender bias and age profile and to identify cohorts who are maintaining mumps virus in circulation.Study design2600 cases of acute mumps infection, as determined by the presence of mumps-specific IgM in sera and oral fluids, were confirmed at the National Virus Reference Laboratory.ResultsAcute mumps infection occurred more frequently in males with a ratio of approximately 2:1 in the 1–9 and 10–19 years old age groups. A 3:2 ratio was observed in the 20–29 years old cohort and the 30+ age group did not show a gender bias. Serological evidence of prior immunological exposure to mumps virus, as determined by the presence of mumps-specific IgG, was high and similar in males and females of all age cohorts (93.1–100%). A significant increase in the number of acute mumps cases in the ≥30 years old age group was observed. This increase was most striking in the periods between the outbreaks (71.1% in 2007 and 56.2% in 2010).ConclusionsAcute mumps infection showed a male gender bias. The consistent and significant increase of mumps infection in the ≥30 years old age group which is also evident in the periods between outbreaks suggests that this may be the cohort maintaining the mumps virus in circulation.