Mumps outbreak in an unimmunized population – Luanshya District, Copperbelt Province, Zambia, 2015

Introduction: Mumps is a vaccine-preventable viral disease that may cause deafness, orchitis, encephalitis or death. However, mumps vaccine is not included in Zambia’s Expanded Program for Immunization. In January 2015, Integrated Disease Surveillance and Response data revealed an increase in reported mumps cases in Luanshya District. We investigated to confirm the etiology and generate epidemiological data on mumps in Zambia. Methods: We conducted active case finding, examined possible case-patients, and administered a standard questionnaire. A suspected mumps case was defined as acute onset of salivary gland swelling in a Luanshya resident during January-June 2015. Eight case-patients provided serum samples to test for mumps-specific immunoglobulin IgM, and buccal swabs to test for mumps viral RNA by RT-PCR, and genotyping of mumps virus at the Centers for Disease Control and Prevention, Atlanta, Georgia, USA. Results: From January – June 2015, a total of 283 mumps cases were reported in Luanshya, peaking in April (71 cases) and clustering (81%) in two townships. Of 72 suspected case-patients interviewed, 81% were aged < 15 years (29%, 1-4 years) and 61% were female. Common clinical characteristics were buccal tenderness (29%) and fever > 37.5ºC (29%). Mumps virus genotype D was confirmed in five case-patients who tested positive by RT-PCR; six case-patients were sero-positive for anti-mumps IgM antibodies (total seven lab-confirmed cases). Conclusion: Our findings represent the first reported epidemiologic description of mumps in Zambia. While the epidemiology is consistent with prior descriptions of mumps in unimmunized populations and no serious complications arose, this report provides data to inform policy discussions regarding mumps vaccination in Zambia.