Estimated Number of Mumps Cases Based on Clinical and Laboratory Data from Sentinel Surveillance in Kanazawa, Japan.

Currently, the mumps vaccine is not routinely recommended in Japan. Adding the mumps vaccine to the routine vaccination program requires an accurate estimation of the mumps viral infection disease burden. However, no precise estimate exists in Japan because mumps surveillance is sentinel surveillance with a reporting definition consisting only of a clinical diagnosis (parotid swelling). Since parotid swelling can be caused by pathogens other than the mumps virus, the estimation of mumps cases using the current surveillance data is inaccurate. To accurately ascertain the burden of disease, we estimated the burden using the results of tests performed at a single sentinel site for laboratory-based surveillance during the mumps endemic (Week 14, 2015, to Week 13, 2016) in Kanazawa. The estimated number of mumps cases based on laboratory-confirmed cases was 3,881 (95% confidence interval: 3,404-4,357), approximately 1,000 cases fewer than the estimated number based on clinically compatible mumps cases. Although the estimated number of mumps cases based on laboratory-confirmed cases was less than that of clinically compatible cases, the frequency of hearing loss due to mumps could potentially be 40% higher than that currently reported. To make the argument for routine mumps vaccination, surveillance using diagnostic testing information is important.