Importance of clinical features in diagnosis of mumps during a community outbreak.

Eleven patients with classical clinical features of mumps presented to one practice over a three month period. Initial laboratory testing for mumps virus specific IgM was positive in only two of the eleven cases. On subsequent testing by an additional system, four additional cases were IgM positive. Five were IgM negative by both assays. Some currently used serological tests for diagnosis of mumps virus infection may be negative in a high proportion of patients with clinically apparent mumps. This series illustrates that the time during the acute illness at which testing is performed may be important and that isolated serological tests cannot be relied upon to exclude a clinical diagnosis of mumps.