Investigation of Mumps Outbreak in a Rural District, Thailand, June – October 2010

Abstract

Background: A mumps outbreak was detected by a nurse at outpatient department of Pua Crown Prince Hospital in Nan Province in September 2010. The investigation was initiated by the joint Surveillance and Rapid Response Team to verify a diagnosis and confirm outbreak, describe epidemiological characteristic, implement control measures and study MMR vaccine effectiveness.
Methods: A descriptive study was conducted in the hospital through the reviews of medical records, interviews with cases, their families, neighbors, physicians, health authorities, and calculating the secondary attack rate within households in 2 villages. Active case finding was performed with a case definition of acute swelling or diagnosed acute lymphadenitis at pre-auricular or submandibular or submental area or diagnosed mumps with the onset during 1 June to 13 October 2010. Laboratory-confirmed cases were found through IgM by ELISA, viral PCR or isolation from buccal swabs. A prospective cohort study was applied to evaluate vaccine effectiveness after mass MMR vaccination among children of 1-6 years age-group in 10 sub-districts.
Results: Until 13 October 2010, 129 suspect mumps cases (attack rate=0.2%) were found in 11/12 subdistricts, 68% of cases were in children <7 years. In kindergarteners, the highest attack rate was 34% (36/107). 10 laboratory-confirmed cases included 6 IgM and 4 mumps virus genotype J by PCR. Secondary attack rate was 25% among household members. A single dose of MMR vaccine was administered to 2,984 (78%) children and the vaccine effectiveness was estimated 65% (95%CI = -55%, 92%).
Conclusions: A genotype J mumps outbreak in Pua District, Nan Province occurred between June and October 2010, affected mainly 1-6 year’s children. Vaccine effectiveness was modest (65%) and the vaccine coverage of 78.3% had resulted in a successful outbreak control 5 weeks afterward.