Presence of low mumps-specific IgG in oral fluids is associated with high mumps viral loads.

Abstract

Mumps outbreaks continue to occur in highly vaccinated populations. Although the diagnosis of mumps is primarily based on clinical symptoms, other viral infections such as parainfluenza can manifest in a similar manner. Therefore, laboratory confirmation of mumps virus infection is important. The aims of this study were to examine mumps cases during the January 2018 to March 2019 period in Ireland as well as to evaluate the association between mumps RNA viral loads, mumps IgG levels, age and gender among patients with laboratory-confirmed mumps virus infection. Oral fluid samples requested for mumps RNA testing (n = 1296) were included in the study. The mumps N gene was detected by real time PCR and reported as Ct values. The proportion of samples received monthly with detectable mumps RNA increased from 10.26%-70.3% during the recent outbreak. Acute mumps cases occurred predominantly in the 16-25 years old age cohort (67.5 %) and in males (55.9 %). Mumps RNA viral loads were significantly higher in females (p < 0.001). During the outbreak, a significantly higher proportion of samples had Ct <30 (p < 0.05). A significant correlation was observed between mumps IgG levels and Ct values in oral fluid samples (p < 0.0001). The presence of low mumps virus-specific IgG in oral fluids is significantly associated with high mumps viral loads. Our findings show that mumps virus is maintained in circulation in the non-outbreak period and acute mumps cases occur predominantly in the MMR vaccinated young adult male population.