Seroepidemiology of the recent mumps virus outbreaks in Ireland

BACKGROUND:

Two recent mumps outbreaks have occurred in Ireland in 2004/2005 and 2008/2009.

OBJECTIVES:

To retrospectively investigate any potential shifts in the gender bias and age profile and to identify cohorts who are maintaining mumps virus in circulation.

STUDY DESIGN:

2600 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.

RESULTS:

Acute 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).

CONCLUSIONS:

Acute 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.