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Module II Graphic Depiction of an Outbreak: Creating an Epidemic Curve.

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Presentation on theme: "Module II Graphic Depiction of an Outbreak: Creating an Epidemic Curve."— Presentation transcript:

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2 Module II Graphic Depiction of an Outbreak: Creating an Epidemic Curve

3 Goal To enable users to create and interpret an epidemic curve Learning Objectives Define an epidemic curve Explain the utility of epidemic curves Describe methods to create epidemic curves

4 Part I Creating an Epidemic Curve

5 1.Verify the diagnosis and confirm the outbreak 2.Define a case and conduct case finding 3.Tabulate and orient data: time, place, person 4.Take immediate control measures 5.Formulate and test hypothesis 6.Plan and execute additional studies 7.Implement and evaluate control measures 8.Communicate findings Basic Steps to an Outbreak Investigation

6 Epidemic Curves Defined A graphic depiction of the progression of an outbreak over time Can provide information about: Size of the outbreak Time trend of the outbreak Person or place information Period of exposure Incubation period

7 Key Terms Exposure period Incubation period

8 What does an epi curve look like? Epi curves are bar graphs (histograms) No space between x-axis categories Each axis is clearly labeled A descriptive title is included

9 x-axis y-axis Components of an Epi Curve

10 Drawing an Epi Curve Refer to line listing data Plot the date a person became ill (date of illness onset) on the x-axis Plot the number of persons who became ill (cases of disease) on each date reported on the y-axis

11 Choosing the best unit of time for the x-axis Day of illness onset is best Hour of onset appropriate for very short incubation period Week or month of onset appropriate for very long incubation period

12 Activity: Creating an Epi Curve

13 Outbreak Scenario In December 2003, an outbreak of E. coli 0157 occurred among tenth-grade students from City High School. The students traveled between December Although the students were broken down into smaller groups, the itineraries were similar for each group. Teachers and other adult chaperones accompanied the students, but no adult reported illness. In addition, no illness was reported among students who did not go on the field trip, and no cases of E. coli 0157 were reported in the community that week. Symptoms of gastroenteritis include severe abdominal pain and/or diarrhea and the average incubation period is 3-4 days.

14 Line listing of 10 cases Patient #AgeSexOnset Date Severe Abdominal Pain No. Times Diarrhea Stool Testing 117MDec 8Y3Not Done 216FDec 6N1Negative 316MDec 10Y2E. coli FDec 8Y3Not Done 516FDec 5Y8E. coli MDec 7Y3Negative 717MDec 7Y3E. Coli FDec 9Y3E. Coli FDec 7N1Negative 1017FDec 6Y3Not Done

15 Drawing an Epi Curve using Pen and Paper 1.Draw the x and y axes 2.Divide each axis into the appropriate measure (unit of time for the x-axis and count for the y-axis) 3.Label 4.Graph each case for the selected period of time 5.Title

16 Using Excel to Create Epi Curves To create an epi curve in Microsoft Excel: –Highlight data to be included in chart –Click the Chart wizard on the tool bar –Choose Column as the chart type –Click Next twice and specify the chart options –Click Next –Click Finish –Change the Gap width to 0 to get the bars to touch

17 1. Enter data in Excel and sort by date

18 2. Total cases for each date

19 3. Highlight data, click on chart wizard and select column as the chart type

20 4. Confirm data selected is correct, click next

21 5. Add descriptive title and label axes clearly

22 6. Change Gap Width to 0 NOTE: Double click on bars in graph to access format data series box

23 7. Adjust axis units (if needed)

24 Completed Epi Curve

25 A real life example Source:

26 Source:

27 Part II Interpreting an Epidemic Curve

28 Epidemic Curve A picture of the number of cases on the dates of illness onset Provides outbreak information including : –Pattern of spread –Size –Outliers –Time trend –Period of exposure –Disease incubation period

29 1.Verify the diagnosis and confirm the outbreak 2.Define a case and conduct case finding 3.Tabulate and orient data: time, place, person 4.Take immediate control measures 5.Formulate and test hypothesis 6.Plan and execute additional studies 7.Implement and evaluate control measures 8.Communicate findings Basic Steps to an Outbreak Investigation

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31 Outbreak Pattern of Spread The overall shape of the epi curve can reveal the type of outbreak 3 types of epi curves: Common source Point source Propagated

32 Point Source Outbreak Characteristics: Brief period of exposure All cases in one incubation period Typically a sharp upward slope and a gradual downward slope

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34 Common Source Outbreak Two types of exposure: Continuous Intermittent

35 Continuous Common Source Outbreak Characteristics: Long period of exposure Gradual increase in cases Then a plateau in number of cases

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37 Intermittent Common Source Outbreak Characteristics: Brief, sporadic exposure period Irregular peaks reflect timing and extent of exposure

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39 Propagated Outbreak Characteristics: Spreads from person to person Longer lasting than common source outbreaks Multiple waves possible Progressively taller peaks

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41 Additional Information from Epi Curves Size of the outbreak Time trend of the outbreak Person or place information Period of exposure Incubation period

42 Outbreak Outliers Very first and last cases on curves that may not appear to be related to the outbreak May represent: –Baseline level of illness –Outbreak source –A case exposed earlier or later than others –An unrelated case –A case with a long incubation period

43 Additional Information Gained from an Epi Curve

44 What type of epidemic curve does the following graph illustrate?

45 Questions?

46 References 1.Last, JM. A Dictionary of Epidemiology. Oxford Univ Press, Nelson, KE and Williams CM. Infectious Disease Epidemiology Theory, and Practice. Jones and Bartlett, 2nd edition, Focus Series: Epidemic Curves Ahead. UNC Chapel Hill School of Public Health North Carolina Center for Public Health Preparedness training materials. 4.I is for Investigation, Session I: Recognizing an Outbreak. UNC Chapel Hill School of Public Health North Carolina Center for Public Health Preparedness. 5.CDC Investigation Update: Outbreak of Salmonella Typhimurium Infections, 2008–

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