NURS 440 Week 3 Epidemiology Case Study Example

Epidemiology Case Study: Investigating a Gastroenteritis Outbreak After a Church Fellowship Dinner

Part 1: Descriptive Epidemiology

On a Monday in February, two families phoned the local health district to report vomiting and diarrhea that began after a church's Saturday evening fellowship dinner. Sixty-four people attended, and the church provided a list of attendees. Maurer and Smith (2013) describe outbreak investigation as beginning with confirmation of the outbreak and a clear case definition, followed by a systematic description of cases.

Case definition: A person who attended the church dinner on Saturday and developed vomiting or three or more loose stools within 72 hours afterward.

All 64 attendees were interviewed by phone with a standard questionnaire covering symptoms, onset time and foods eaten. Thirty-one people met the case definition.

Person: Cases ranged in age from 6 to 81 years, with no clear difference by sex. Most cases reported vomiting (84%), diarrhea (77%) and nausea; fewer reported low-grade fever. Illness lasted 24 to 48 hours. Two older adults visited an emergency department for dehydration, and none was admitted.

Place: All cases attended the dinner; no illness was reported among church members who did not attend.

Time: Onsets began about 18 hours after the meal, rose to a peak between 30 and 36 hours and ended by 54 hours. The epidemic curve showed a single peak with a rapid rise and fall, the signature of a single shared exposure at one meal. Three later cases among household members of ill attendees appeared after the main peak and were excluded under the case definition but noted as possible secondary spread.

Part 2: Analytic Epidemiology

The overall attack rate was 31 ill out of 64 attendees, or 48.4%. Food-specific attack rates were calculated for each dish served.

For chicken salad, the attack rate among those who ate it was 27 divided by 36, or 75.0%, and among those who did not eat it, 4 divided by 28, or 14.3%. The relative risk is 75.0 divided by 14.3, or about 5.25: illness was roughly five times more common among those who had chicken salad than among those who skipped it. The other three dishes had relative risks close to 1, meaning illness was about as common whether or not people ate them. The four ill people who did not report eating chicken salad may have misremembered what they ate or taken a spoonful without noticing, a common problem with food histories, or may have been infected another way, such as by contact with ill people or contaminated serving utensils.

The agent is most likely norovirus. The incubation period of roughly 18 to 54 hours, the predominance of vomiting, the short illness and the February timing all fit. National surveillance shows that norovirus outbreaks in the United States follow a winter season, generally from October to May (Kambhampati et al., 2023). Stool testing of three ill attendees was requested to confirm the agent. Laboratory confirmation matters because other agents, such as some bacterial toxins, can cause similar outbreaks with shorter incubation periods, and the control measures differ.

How did the salad become contaminated? The volunteer who prepared it reported vomiting on the Thursday before the dinner and felt well by Friday, when she cooked. Holst et al. (2025), analyzing 2,677 foodborne outbreaks reported nationally from 2014 to 2022 with contributing factor data, found that contamination factors, problems that allow pathogens to get into food, were present in more than 80% of outbreaks in each period studied. A recently ill food handler preparing a dish that is not cooked after handling is a classic contamination pathway.

Control and Prevention

Immediate measures include advising ill people to stay home until 48 hours after symptoms resolve, teaching thorough handwashing with soap and water, since alcohol gel is less effective against norovirus, and cleaning surfaces in the church kitchen with a bleach-based disinfectant. For prevention, the community health nurse can work with the church to adopt a simple food safety policy: no one prepares food for church events within 48 hours of vomiting or diarrhea, gloves and utensils are used for ready-to-eat foods and handwashing supplies are stocked at every event. The nurse can also offer a short food safety talk for the church's kitchen volunteers before the next fellowship dinner. The relative risk pointed to a salad, but the prevention plan has to reach the person who made it and every volunteer who will cook next.

References

Holst, M. M., Wittry, B. C., Crisp, C., Torres, J., Irving, D. J., & Nicholas, D. (2025). Contributing factors of foodborne illness outbreaks: National Outbreak Reporting System, United States, 2014-2022. MMWR Surveillance Summaries, 74(1), 1-12. https://doi.org/10.15585/mmwr.ss7401a1

Kambhampati, A. K., Calderwood, L., Wikswo, M. E., Barclay, L., Mattison, C. P., Balachandran, N., Vinjé, J., Hall, A. J., & Mirza, S. A. (2023). Spatiotemporal trends in norovirus outbreaks in the United States, 2009-2019. Clinical Infectious Diseases, 76(4), 667-673. https://doi.org/10.1093/cid/ciac627

Maurer, F. A., & Smith, C. M. (2013). Community/public health nursing practice: Health for families and populations (5th ed.). Elsevier Saunders.