Mumps Cases Disproportionately Affecting Persons Living with HIV Infection and Men Who Have Sex with Men - Chicago, Illinois, 2018.

During January 1-March 2, 2018, the number of mumps cases among adults reported to the Chicago Department of Public Health (CDPH) doubled compared with the same period in 2017. In response, CDPH created a supplementary questionnaire to collect additional information on populations affected and potential transmission routes. An epidemiologic analysis of routine and supplementary data, including spatiotemporal analysis, was performed to describe mumps cases reported to CDPH during 2018. A fourfold increase in mumps cases was reported during 2018 compared with 2017, with men who have sex with men (MSM) and persons living with human immunodeficiency virus (HIV) infection disproportionately represented among cases. A spatiotemporal, residential cluster was identified in a 9-square-mile area within six adjacent communities. The majority of persons affected were MSM, and this area was visited by many other persons with mumps diagnoses. Spatiotemporal analyses could be used in real time to identify case clusters to target public health response efforts, including to guide recommendations for additional measles, mumps, and rubella (MMR) vaccine and to identify specific transmission venues.