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An outbreak of mumps in Sweden, February-April 2004
B Sartorius1,2, P Penttinen1, J Nilsson1,3
1Department of Epidemiology, Swedish Institute for Infectious Disease Control (SMI), Solna, Sweden.
Abstract:
Between 24 February and 26 April 2004, Västra Götaland county in Sweden reported 42 cases of suspected mumps. A descriptive study of the cases was undertaken. A questionnaire was administered by telephone and vaccine effectiveness was calculated using the screening method. Seventy four per cent (31/42) of the suspected cases were interviewed by telephone. Eight out of the 42 serum samples were positive or equivocal for mumps IgM by ELISA. Mumps virus genome was identified in 21/42 (50%) saliva samples. Eleven were selected for sequencing and all were confirmed to be mumps virus. Cases were predominantly from 2 small towns. Eighteen out of 19 cases that developed bilateral swelling could be linked to one small town. The median age of interviewed cases was 43 years (range 5 to 88). Six cases were admitted to hospital, 5 of which were older than 30 years. The highest incidence occurred in the 35 to 44 years age group. Vaccine effectiveness was estimated to be 65% for 1 dose and 91% for 2 doses. This descriptive study shows the increasing age of mumps cases with increasing vaccine coverage. Vaccine effectiveness was particularly high for 2 doses. Second-dose uptake must be ensured, as primary vaccine failure is well documented in mumps. Stronger precautions must be taken to avoid pools of susceptible older individuals accumulating due to the increased risk of complications.
Insights
This study found that mumps cases are increasingly affecting older adults, especially those with only one dose of the measles, mumps, and rubella (MMR) vaccine. Two doses of the MMR vaccine demonstrated high effectiveness in preventing mumps.
Area of Science:
- Epidemiology
- Virology
- Public Health
Background:
- Mumps outbreaks can occur even with high vaccination coverage.
- Understanding age distribution and vaccine effectiveness is crucial for control strategies.
Purpose of the Study:
- To describe the characteristics of a mumps outbreak in Sweden.
- To evaluate the effectiveness of the measles, mumps, and rubella (MMR) vaccine.
Main Methods:
- Descriptive epidemiological study of 42 suspected mumps cases.
- Telephone questionnaires and serological testing (ELISA for IgM).
- Viral genome identification in saliva samples and sequencing.
Main Results:
- Mumps virus confirmed in 50% of saliva samples; cases predominantly in adults (median age 43).
- Highest incidence in the 35-44 age group, with complications more frequent in older individuals.
- Vaccine effectiveness estimated at 65% for one dose and 91% for two doses.
Conclusions:
- Mumps cases are shifting to older age groups with increased vaccination coverage.
- Two-dose MMR vaccine coverage is essential for high effectiveness and preventing complications.
- Strategies are needed to prevent susceptible older adult populations due to primary vaccine failure.
