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Challenges in Interpretation of Diagnostic Test Results in a Mumps Outbreak in a Highly Vaccinated Population
L A Trotz-Williams1, N J Mercer2, K Paphitis2
1Wellington-Dufferin-Guelph Public Health, Guelph, Ontario, Canada Lise.Trotz-Williams@wdgpublichealth.ca.
Abstract:
In spite of a greatly reduced incidence rate due to vaccination, mumps outbreaks continue to occur in several areas of the world, sometimes in vaccinated populations. This article describes an outbreak in a highly vaccinated population in southwestern Ontario, Canada, and the challenges encountered in interpreting the results of diagnostic tests used in the outbreak. During the outbreak, patients were interviewed and classified according to the outbreak case definition, and specimens were collected for diagnostic testing according to Ontario guidelines. Twenty-seven individuals were classified as confirmed cases (n = 19) or suspect cases (n = 8) according to the case definition, only 9 of which were laboratory-confirmed cases: 7 confirmed by reverse transcriptase PCR (RT-PCR) and 2 by IgM serology. All 19 confirmed cases represented patients who were associated with secondary schools in the local area and had been vaccinated against mumps with one (n = 2) or two (n = 17) doses of the measles-mumps-rubella (MMR) vaccine. This is the first published report of an outbreak of mumps in Ontario in which all confirmed cases had been vaccinated against the disease. It highlights the limitations of and difficulties in interpreting current mumps diagnostic tests when used in vaccinated individuals.
Insights
Mumps outbreaks can occur even in highly vaccinated populations. This study found that diagnostic tests for mumps were challenging to interpret in vaccinated individuals during an outbreak.
Area of Science:
- Epidemiology
- Infectious Diseases
- Public Health
Background:
- Mumps incidence has decreased due to vaccination, but outbreaks persist, even in vaccinated groups.
- Understanding these outbreaks is crucial for effective public health strategies.
- Diagnostic challenges in vaccinated populations require further investigation.
Purpose of the Study:
- To describe a mumps outbreak in a highly vaccinated population in Ontario, Canada.
- To highlight challenges in interpreting diagnostic test results for mumps in vaccinated individuals.
- To report the first documented outbreak in Ontario where all confirmed cases were vaccinated.
Main Methods:
- Patient interviews and classification using outbreak case definitions.
- Specimen collection for diagnostic testing following Ontario guidelines.
- Laboratory confirmation using reverse transcriptase PCR (RT-PCR) and IgM serology.
Main Results:
- Twenty-seven individuals were classified as confirmed (19) or suspect (8) cases.
- Only 9 cases were laboratory-confirmed (7 by RT-PCR, 2 by IgM serology).
- All 19 confirmed cases had received one or two doses of the measles-mumps-rubella (MMR) vaccine.
Conclusions:
- Mumps outbreaks can occur in highly vaccinated populations.
- Current mumps diagnostic tests present interpretation difficulties in vaccinated individuals.
- This outbreak underscores the need for improved diagnostic strategies for mumps in vaccinated populations.
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