Virus genotypes and responses of serum-specific antibodies in children with primary mumps and mumps reinfection.

BACKGROUND: Research on children with mumps reinfection after natural infection is limited; there are currently no studies on virus-specific antibody responses in paired sera or genotyping of isolated viruses. METHODS: This study included 281 children (147 boys and 134 girls, age: 1.2-15.9 y) with primary mumps (240), mumps reinfection after natural infection (9), mumps after previous vaccination (26), and vaccine-associated mumps (6). We measured mumps-specific serum antibodies and analyzed isolated virus genes. RESULTS: During acute illness, series-specific IgM and IgG titers exceeded cutoff values in 240 and 232 children with primary mumps, respectively. During convalescence, IgM antibodies were positive in seven and negative in two of nine children with mumps reinfection occurring after natural infection; among 26 previously vaccinated children, 13 were positive and 13 negative. Mumps viruses were isolated from viral cultures from 42 of the 51 children. Except for 6 vaccine-associated cases, all remaining 36 cases of isolated mumps virus were identified as genotype G. CONCLUSION: These results suggest that measurement of IgM antibody on any day of acute illness may be indicative of primary mumps but may be inconsistent for diagnosing mumps reinfection after natural infection or previous vaccination.