oswego DONE

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Indiana University, Purdue University, Indianapolis *

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300

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Medicine

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Feb 20, 2024

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PART I - Background On April 19, the local health officer in Oswego County, reported an occurrence of an outbreak of acute gastrointestinal illness to the District Health Officer. Dr. Rubin, epidemiologist-in-training, was assigned to investigate. When Dr. Rubin arrived in the field, he learned from the health officer that all persons known to be ill attended a church supper held on the previous evening, April 18th. Family members who did not attend the church supper did not become ill. Accordingly, Dr. Rubin focused the investigation on the supper. He completed interviews with 75 of the 80 persons known to have attended, collecting information about the occurrence and time of onset of symptoms, and foods consumed. Of the 75 persons interviewed, 46 persons reported gastrointestinal illness. Question 1: Would you call this an epidemic? Would you call it an outbreak? This is an outbreak. The agent has not been Identified. The incidence is much higher than endemic rates of gastroenteritis, and the disease has not traveled outside of the group of people at the church supper, therefore isolating it to an outbreak. Question 2: List the steps of an outbreak investigation. 1. Verify diagnosis 2. Define a case 3. Identify and count cases 4. Compare observed with expected 5. Rule out other reasons for increase ! Clinical Description The onset of illness in all cases was acute, characterized chiefly by nausea, vomiting, diarrhea, and abdominal pain. None of the ill persons reported having an elevated temperature; all recovered within 24 to 30 hours. Approximately 20% of the ill persons visited physicians. No fecal specimens were obtained for bacteriologic examination. I Question 3: List the broad categories of diseases that must be considered in the differential diagnosis of an outbreak of gastrointestinal illness. Consider using CDC webpage regarding potential etiological agents for GI illnesses Bacterial: bacteria is a likely contender in this outbreak. Bacterium like E. coli and Listeria are often agents for GI illnesses Parasite/protazoa like giardia can cause GI illness but this is not as common

Norovirus also causes GI illness The investigators suspected that this was a vehicle-borne outbreak, with food as the vehicle. Question 4: In epidemiologic parlance, what is a vehicle? What is a vector? What are other modes of transmission? A vehicle is a substance that carries disease, like food, water, blood etc. A vector is a living transporter of disease, like a parasite. One example of a vector is mosquitos that carry malaria. Question 5: If you were to administer a questionnaire to the church supper participants, what information would you collect? Group the information into categories. Dr. Rubin put his data into a line listing. I would ask demographic questions in order to see if the disease effects different populations more or less on a biological basis. This would include age, sex and race. I would obtain information on what they did and did not eat in order to determine where the GI illness originated in the food. I would ask about specific symptoms and onset of disease in order to narrow down what agent could have caused this, before being able to physically test for it. Question 6: What is a line listing? What is the value of a line listing? A line listing is a data table presenting outbreak information. It is used to compare data between cases, find similarities and differences, and identify patterns. PART II Description of the Supper The supper was held in the basement of the village church. Foods were contributed by numerous members of the congregation. The supper began at 6:00 p.m. and continued until 11:00 p.m. Food was spread out on a table and consumed over a period of several hours.

Data regarding onset of illness and food eaten or water drunk by each of the 75 persons interviewed are provided in the attached line listing. The approximate time of eating supper was collected for only about half the persons who had gastrointestinal illness. Question 7: What is the value of an epidemic curve? The epidemic curve shows us the estimated time of contact with the agent, as well as onset of disease. If we can figure out the curve, we can see what food was served when and determine other factors. I Question 8: Construct an epidemic curve and graph the cases by time of onset of illness (include appropriate labels and title). What does this graph tell you?

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Graph by Kendra Swinney

This tells me when symptoms began, helping us determine the agent and see outliers Question 9: Are there any cases for which the times of onset are inconsistent with the general experience? How might they be explained? Yes, a few times are more prevalent than others. This could purely be because of the amount of people that ate a few hours before that time, or this could be another factor like consuming more than one contaminated food, how long the food sat out etc. PART Ill Question 10: Where possible, using the line listing, calculate incubation periods and illustrate their distribution with an appropriate graph. Avg. incubation period in hours: 5.86

Question 11: Determine the range and median of the incubation period. Range: 18 - 3 = 15 hr Median: 3 + 4 = 7; 7/2 = 3.5

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Question 12: How does the information on incubation period, combined with the data on clinical symptoms, help in the differential diagnosis of the illness? Because there are a few outliers when it comes to incubation periods, I would examine those cases and their symptoms, in order to see if they are any different from those that were closer to the median. This difference could mean that these cases are affected by different agents, or the inverse are affected by more than one agent. This data together also allows us to look through what we know about GI illness and compare these numbers to those of other agents (like E. coli), helping us determine or narrow our results. Question 13: Using the data in the attached line listing, complete the table below. Which food is the most likely vehicle of infection?

Data Table by Grace Hicks Question 14: Outline further investigations that should be pursued. There should be further investigation on those who ate ——-, and possibly stool samples from these cases to solidify what agent we suspect. I would also investigate the sanitization of the church and the hygiene of those who prepared the food. Question 15: What control measures would you suggest?

I would suggest keeping dishes at an appropriate temperature in the future, in order to prevent contamination. I would suggest that guests wear gloves when handling food, practicing hygiene, and separate serving utensils as well. Question 16: Why was it important to work up this outbreak? This is a busy and common social setting, so this could be an issue in the future. Educating and finding the source of outbreaks can prevent further GI illness. Question 17: Refer to the steps of an outbreak investigation you listed in Question 2. How does this investigation fit that outline? 6. Verify diagnosis We could not identify the pathogen based on current tests 7. Define a case Our cases shared place, time, and incubation periods along with symptoms 8. Identify and count cases We identified and analyzed all 75 guests based on illness status, incubation, time of contact and onset of illness. 9. Compare observed with expected Because there was no expected, and GI illness is an endemic, we were able to identify this as an outbreak because of its elevated incidence rate. 10. Rule out other reasons for increase There were no confounding factors in demographic such as age or sex, as well as no confounding in the foods. We must do further investigation on handling, food content etc.

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