Outbreak example Oswego answers PDF

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Microbiology...

Description

The following is an example of an actual investigation that occurred several decades ago. It is a prime example of how to perform an outbreak investigation with little to no lab facilities available to you.

PART I – Background On April 19, 1940, the local health officer in the village of Lycoming, Oswego County, New York, reported the occurrence of an outbreak of acute gastrointestinal illness to the District Health Officer in Syracuse. Dr. A. M. Rubin, epidemiologist-in-training, was assigned to conduct an investigation. When Dr. Rubin arrived in the field, he learned from the health officer that all persons known to be ill had attended a church supper held on the previous evening, April 18. 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 or an outbreak?

What is the definition of each? 1. epidemic –

2. outbreak Epidemic – when a disease is increasing beyond what is expected. Often referred to as an outbreak but an outbreak is usually on a smaller scale and limited to one locale.

Question 2: Review the steps of an outbreak investigation. (these have been given to you)

1. Identify investigation team and resources 2. Establish the existence of an outbreak 3. Verify the diagnosis 4. Construct a working case definition 5. Case Finding: find cases systematically and develop line list 6. Perform descriptive epidemiology and develop hypotheses 7. Evaluate hypotheses and perform additional studies (as necessary) 8. Implement control measures 9. Communicate findings 10. Maintain surveillance

Question 3: What are the two ways that food-borne bacteria can make you sick and what is the general time frame for each? Growth in the digestive system, which may take a few hours to days, and toxins which may take as little as 30 minutes (relatively fast).

Could this event be viral? It’s possible, you don’t know yet.

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 (remember, this is 1940).

Question 4: What is a vehicle? What is a vector? What are other modes of transmission? The investigators suspected that this was a vehicle-borne outbreak, with food as the vehicle. A vehicle is an inanimate object that can transmit infectious agents

A vector is an animal that transmits (or can transmit) an infectious agent from one host to another. There are two kinds of vectors: 1) biological vector and 2) mechanical vector.

Question 5: If you were to administer a questionnaire to the church supper participants, what information would you collect? Age, sex, time of meal, whether or not they got ill, date and time of onset, foods eaten; symptoms.

Question 6: What is the value of a line listing? What is the value of an epidemic curve? A line list is a table that summarizes information about persons who may be associated with an outbreak. Each row represents a single individual, and each column represents a specific characteristic about that person. Column information includes identifying, demographic, clinical, and other epidemiologic information, including risk factors possibly related to the illness. A line list helps organize preliminary information gathered during the early part of an outbreak investigation. As the investigation progresses, the line list can be updated. Line listings can be created by hand (paper copy) or on a computer. One advantage of creating an electronic line list is that frequency distributions and epidemic curves can be generated rapidly. The information that goes into a line list is generally collected on a questionnaire. The important elements from the questionnaire are then used to create a line list.

An epidemic curve is a graph in which the number of new cases of a disease is plotted against an interval of time to describe a specific epidemic or outbreak. This should help determine possible causes.

Question 7: Look at the line list. How could the data in the line listing be better presented? There’s a lot of information and the date could be presented in a more reader friendly format. Perhaps, with all the ill persons separated from the non-ill.

Question 8: Using the graph paper provided, graph the cases by time of onset of illness (include appropriate labels and title). What does this graph tell you? The graph should give you a good idea of how long it took for the organism to make the people involved ill. Again, this should allow you to narrow your organism.

Question 9: Are there any cases for which the times of onset are inconsistent with the general experience? How might they be explained?

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.

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59

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