Australian mumps serosurvey 2012–2013: any cause for concern?

Abstract

Objective To determine population-level immunity to mumps in Australia. Methods We tested randomly selected specimens from people aged 1–49 years using the Enzygnost anti-parotitis IgG enzyme immunoassay from an opportunistically collected serum bank in 2012–2013. Weighted estimates of the proportion seropositive and equivocal for mumps-specific IgG antibody were determined by age group and compared with two previous national serosurveys conducted in 2007–2008 and 1997–1998. Results Overall, 82.1% (95% CI 80.6–83.5%) of 2,729 specimens were positive or equivocal for mumps-specific IgG antibodies (71.1% positive [95% CI 69.4–72.9%]; 10.9% equivocal [95% CI 9.8–12.2%]). The proportion positive or equivocal was higher in 2012–2013 (82.1%) than in 2007–2008 (75.5%) and 1997–1998 (72.5%), but varied by age. The proportion positive or equivocal in 2012-2013 was above 80% for all age groups older than 1 year except for 30–34 year olds, corresponding to the 1978–1982 birth cohort previously identified as most likely to have missed out on a second MMR vaccine dose. Conclusions Seropositivity to mumps in 2012–2013 was well-maintained compared with previous serosurveys. Low mumps notifications over this period in Australia suggest an absence of community-based transmission of mumps infection in the general population, but recent outbreaks among Aboriginal adolescents and young adults in close-contact settings, despite high 2-dose MMR coverage, suggest that seroprotection may be insufficient in other similar settings in Australia.