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Mumps in a highly vaccinated Marshallese community in Arkansas, USA: an outbreak report
Virgie S Fields1, Haytham Safi2, Catherine Waters2
1Arkansas Department of Health, Little Rock, AR, USA; Council of State and Territorial Epidemiologists Applied Epidemiology Fellowship, Atlanta, GA, USA.
Background:
During 2000-15, Arkansas Department of Health, Little Rock, AR, USA, investigated between one and six cases of mumps each year. From Aug 5, 2016, to Aug 5, 2017, the department received notification of more than 4000 suspected mumps cases in the second largest outbreak in the USA in the past 30 years.
Methods:
Arkansas Department of Health investigated all reported cases of mumps to ascertain exposure, travel, and vaccination histories and identify close contacts. Cases were classified as confirmed if the patient had laboratory confirmation of mumps virus or probable if they had clinical symptoms and either a positive serological test or a known epidemiological link to a confirmed case.
Findings:
2954 cases of mumps related to the outbreak were identified during the outbreak period: 1665 (56%) were laboratory confirmed, 1676 (57%) were in children aged 5-17 years, and 1692 (57%) were in Marshallese people. Among the 1676 school-aged cases, 1536 (92%) had previously received at least two doses of a vaccine containing the mumps virus. Although 19 cases of orchitis were reported, severe complications were not identified. Unusual occurrences, such as recurrent parotitis and prolonged viral shedding, were observed mostly in Marshallese individuals. Viral samples were characterised as genotype G.
Interpretation:
This large-scale outbreak, primarily affecting a marginalised community with intense household crowding, highlights the need for coordinated, interdisciplinary, and non-traditional outbreak responses. This outbreak raises questions about mumps vaccine effectiveness and potential waning immunity.
Funding:
Council of State and Territorial Epidemiologists and US Centers for Disease Control and Prevention.
Insights
A large mumps outbreak in Arkansas primarily affected the Marshallese community, with many cases occurring in vaccinated children. This event questions mumps vaccine effectiveness and highlights the need for tailored public health responses.
Area of Science:
- Epidemiology
- Public Health
- Infectious Diseases
Background:
- Arkansas experienced a significant mumps outbreak from August 2016 to August 2017, with over 4000 suspected cases.
- This contrasts sharply with the 1-6 annual cases reported between 2000-2015.
Purpose of the Study:
- To investigate the epidemiology of a large-scale mumps outbreak in Arkansas.
- To identify risk factors, affected populations, and clinical characteristics associated with the outbreak.
- To evaluate vaccine effectiveness and understand unusual disease presentations.
Main Methods:
- Active case finding and investigation by the Arkansas Department of Health.
- Classification of cases as confirmed (laboratory confirmation) or probable (clinical symptoms with serological or epidemiological link).
- Data collection on exposure, travel, vaccination history, and close contacts.
Main Results:
- 2954 mumps cases were identified, with 56% laboratory-confirmed.
- The majority of cases (57%) were in children aged 5-17 years and Marshallese individuals (57%).
- Notably, 92% of school-aged cases had received at least two doses of the mumps vaccine; severe complications were rare, but unusual presentations were observed in the Marshallese population.
Conclusions:
- The outbreak underscores the need for coordinated, interdisciplinary public health interventions, especially for marginalized communities with high-density housing.
- The findings raise critical questions regarding the effectiveness of the mumps vaccine and the potential for waning immunity over time.
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