PUBH 3100 Week 8 Infectious Condition Paper Example

Working Backward From Forty-Two Cases: A Mumps Outbreak Among Students in a Composite College County, the Points Where Spread Could Have Been Interrupted, and the Testing Change That Inflated the Count First

Student Name

Walden University

PUBH 3100: Human Disease and Prevention

Instructor Name

Month Day, Year

Working Backward From Forty-Two Cases: A Mumps Outbreak Among Students in a Composite College County, the Points Where Spread Could Have Been Interrupted, and the Testing Change That Inflated the Count First

The Outbreak

Over eleven weeks in a composite county that is home to a public university, the health department recorded 42 confirmed or probable cases of mumps, compared with none in the previous two years. Thirty-six cases were students, most living in residence halls; the rest were household or social contacts in the community. Almost every student's record showed two MMR doses, most of them given in early childhood, many years before college. This paper works backward from the cases to the points where exposure could have been interrupted. Before that, it addresses a change in laboratory practice that affected the count.

First, the Count

What Changed

In the fourth week of the outbreak, the university health clinic switched from sending blood tests for mumps antibodies to sending cheek swabs for a PCR test that detects the virus directly, and the state laboratory began accepting swabs from all clinics in the county. PCR on swabs taken early in illness detects mumps more reliably than antibody tests in previously vaccinated people, whose antibody response may not rise in a recognizable way.

What It Did to the Numbers

Before the switch, 9 of 31 tested students with swelling of the salivary glands had a positive result; after it, 27 of 46 did. Part of the apparent acceleration in weeks 4 to 7 therefore reflects better detection rather than faster spread. The paper treats the outbreak's size as at least 42 cases and avoids reading the rise in weeks 4 to 7 as a rise in transmission without adjusting for the testing change. Cases before the switch were probably undercounted, which means the outbreak likely started earlier and was larger at first than the reported curve suggests.

Working Backward: The Chain of Transmission

Table 1

Chain of Transmission and Points of Interruption (Composite Outbreak)

Note. Composite outbreak; interruption points follow published outbreak guidance and trials.

Interruption Points in Detail

Isolation After Symptom Onset

Isolating people for five days after salivary gland swelling begins reduces spread from the most infectious period that can be recognized. In this outbreak, review of case interviews showed that 14 cases attended classes, practices or social events after swelling began, often because the swelling seemed minor or because they did not know it could be mumps. Earlier messages to students describing the symptom and the isolation rule could have shortened that exposure.

A Third Dose of MMR Vaccine

Because nearly every student had received two doses, the outbreak points to waning protection rather than missing vaccination. During a university outbreak in Iowa, a third MMR dose was associated, 28 days later, with 78.1% lower mumps risk compared with two doses, and students whose second dose was given 13 or more years earlier had more than nine times the risk (Cardemil et al., 2017). National vaccine advisors later endorsed a third dose for groups that health officials judge to be at heightened risk during a mumps outbreak (Marin et al., 2018). A university in Illinois made a similar recommendation during its own outbreak (Albertson et al., 2016). In this composite outbreak, the health department recommended a third dose in week 6; earlier action might have prevented some later cases.

Reducing Shared Contact

Sharing drinks and close contact at parties and on the sports team linked several clusters. Advice to stop sharing water bottles, cups and utensils during the outbreak is simple and inexpensive, but its effect is hard to measure, and it depends on students following it at parties.

Why Two Doses Were Not Enough

The outbreak raises an obvious question: if nearly everyone was vaccinated, why did mumps spread? Two explanations fit the evidence. Protection from the mumps component of MMR appears to wane over time, which is consistent with the Iowa finding that students whose second dose was more than 13 years earlier faced much higher risk (Cardemil et al., 2017). In addition, the conditions of residence hall life, with close contact, shared drinks and crowded social events, expose students to large and repeated doses of virus, which can overcome partial immunity. Neither explanation means that vaccination failed. Without high two-dose coverage, a mumps outbreak in a college community would likely be far larger. The lesson is that high coverage reduces outbreaks but does not eliminate them in settings that favor close contact, which is why outbreak-specific measures such as a third dose exist.

What the Outbreak Shows

Working backward shows that the outbreak could not have been stopped at its source, that isolation after symptoms helps only if students recognize symptoms quickly, and that reducing susceptibility through a third dose is the step with the strongest evidence. It also shows that the course of an outbreak cannot be read from a case curve without knowing when testing changed.

Limits

Case interviews depend on recall. Some infections, especially mild ones in vaccinated students, were never tested. The comparison of positive test shares before and after the switch reflects both the test and the students who chose to come in.

References

Albertson, J. P., Clegg, W. J., Reid, H. D., Arbise, B. S., Pryde, J., Vaid, A., Thompson-Brown, R., & Echols, F. (2016). Mumps outbreak at a university and recommendation for a third dose of measles-mumps-rubella vaccine: Illinois, 2015-2016. Morbidity and Mortality Weekly Report, 65(29), 731-734. https://doi.org/10.15585/mmwr.mm6529a2

Cardemil, C. V., Dahl, R. M., James, L., Wannemuehler, K., Gary, H. E., Shah, M., Marin, M., Riley, J., Feikin, D. R., Patel, M., & Quinlisk, P. (2017). Effectiveness of a third dose of MMR vaccine for mumps outbreak control. The New England Journal of Medicine, 377(10), 947-956. https://doi.org/10.1056/NEJMoa1703309

Marin, M., Marlow, M., Moore, K. L., & Patel, M. (2018). Recommendation of the Advisory Committee on Immunization Practices for use of a third dose of mumps virus-containing vaccine in persons at increased risk for mumps during an outbreak. Morbidity and Mortality Weekly Report, 67(1), 33-38. https://doi.org/10.15585/mmwr.mm6701a7