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CDC 24/7: Saving Lives. Protecting People.CDC 24/7: Saving Lives. Protecting People. Quick-Learn Lesson Create an Epi Curve
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 This Quick Learn lesson will take approximately 10 minutes to complete. When you are finished, you will be able to create an epidemic curve, or “epi curve.” You can move through this lesson by using the NEXT and BACK icons below.
 What is an Epi Curve? An **epi curve** is a visual display of the onset of illness among cases associated with an outbreak. You can learn a lot about an outbreak from an epi curve, such as The outbreak's time trend, that is, the distribution of cases over time 
					  			  	Outliers, that is, cases that stand apart from the overall pattern 
					  			  	General sense of the outbreak's magnitude 
					  			  	Inferences about the outbreak's pattern of spread 
					  			  	The most likely time period of exposure
 X and Y Axes An epi curve is represented by a graph with two axes that intersect at right angles. The horizontal **x-axis** is the date or time of illness onset among cases. The vertical **y-axis** is the number of cases. Each axis is divided into equally spaced intervals, although the intervals for the two axes may differ.
 Cases Cases (represented by boxes) are placed along the x-axis according to the date when their earliest symptoms began. If symptoms for more than one case began on the same date (or time), the boxes are stacked one above the other.
 Time Intervals The unit of time for the x-axis is based on the incubation period of the disease under investigation and the length of time over which cases are distributed. As a general rule, the unit of time is set at roughly **1/4** (0.25) of the average **incubation period** for the illness under investigation. **Average incubation period multiplied by .25 = Intervals**
 Time Intervals, continued If the incubation period of an illness is short, the interval on the epi curve might be indicated in hours or even minutes. View the example below The incubation period for infection with *E. coli*
                    O1257:H7 is usually 3–4 days. In this case,
                            you would probably use an interval of one day
                  on the x-axis. **4 days multiplied by 0.25 = 1 day****intervals (4 x 0.25 = 1)**
 Determining a Title An epi curve should have a title that describes it, including the type of illness, the place where the outbreak occurred, and the time period. Cases of [insert illness name] by date of onset, [insert location and time period] View the example below. **Cases of *E. coli* O157:H7 by Date of Onset, Epps, Louisiana, February, 2012**
 Your Turn: Exercise 1 Seven cases of hepatitis A have been reported in Homer, Virginia. Construct the epi curve from the line list below. 
								  
					Select the column heading that you would use to label the x-axis of the epi curve. Case
                                                1
                                                2
                                                3
                                                4
                                                5
                                                6
                                                7 Age
                                                42
                                                31
                                                23
                                                46
                                                54
                                                49
                                                31 Sex
                                                M
                                                M
                                                M
                                                M
                                                M
                                                M
                                                M Date ofOnset
                                                Dec 13
                                                Jan 5
                                                Jan 6
                                                Jan 8
                                                Jan 9
                                                Jan 10
                                                Jan 20 Date ofDiagnosis
                                                Dec 26
                                                Jan 12
                                                Jan 8
                                                Jan 16
                                                Jan 12
                                                Jan 13
                                                Jan 20
 **Exercise 1: Incorrect** That is **incorrect**.
      The correct answer is Date of Onset.
    In an epi curve, the date of illness onset is on the x-axis.
    The number of cases should go on the y-axis.
 **Exercise 1: Incorrect** That is **incorrect**.
      The correct answer is Date of Onset.
    In an epi curve, the date of illness onset is on the x-axis.
    The number of cases should go on the y-axis.
 **Exercise 1: Incorrect** That is **incorrect**.
      The correct answer is Date of Onset.
    In an epi curve, the date of illness onset is on the x-axis.
    The number of cases should go on the y-axis.
 **Exercise 1: Correct** That is **correct**.
      The correct answer is Date of Onset.  
    In an epi curve, the date of illness onset is on the x-axis.
    The number of cases should go on the y-axis.
    Empty epi curve by number of cases by date of onset of illness
 **Exercise 1: Incorrect** That is **incorrect**.
      The correct answer is Date of Onset.
    In an epi curve, the date of illness onset is on the x-axis.
    The number of cases should go on the y-axis.
 Your Turn: Exercise 2 Given that the average incubation period for hepatitis A is 28-30 days, what intervals would you use on the x-axis? 1-day intervals 7-day intervals 28-day intervals **Exercise 2: Incorrect** Given the average incubation period for hepatitis A is 28-30 days, and the unit of time is roughly one-quarter the average incubation period, you would use an interval of 7 days on the x-axis.
    28 X 0.25 = 7
 **Exercise 2: Correct** Given the average incubation period for hepatitis A is 28-30 days, and the unit of time is roughly one-quarter the average incubation period, you would use an interval of 7 days on the x-axis.
    28 X 0.25 = 7
 **Exercise 2: Incorrect** Given the average incubation period for hepatitis A is 28-30 days, and the unit of time is roughly one-quarter the average incubation period, you would use an interval of 7 days on the x-axis.
    28 X 0.25 = 7
 Your Turn: Exercise 3 What is the appropriate title for the epi curve? Hepatitis A outbreak in Virginia Outbreak in Homer, Virginia Hepatitis A Cases by Date of Onset in Homer, Virginia, December 2011–January 2012  **Exercise 3: Incorrect** The title should include both the name of the disease and the place where the outbreak occurred.  The correct title is **Hepatitis A Cases by Date of Onset in Homer, Virginia, December 2011 - January 2012**
 **Exercise 3: Incorrect** The title should include both the name of the disease and the place where the outbreak occurred.  The correct title is **Hepatitis A Cases by Date of Onset in Homer, Virginia, December 2011 - January 2012**
 **Exercise 3: Correct** The title should include both the name of the disease and the place where the outbreak occurred.  The correct title is **Hepatitis A Cases by Date of Onset in Homer, Virginia, December 2011 - January 2012**Empty epi curve for number of cases by onset of symptoms
 Your Turn: Exercise 4 Using the following information from a line listing, which date from the **Options** below represents the Date of Onset for Case 1? **Case**
                          					**Age**
                          					**Sex**
                          					**Date of Onset**
                          					**Date of Diagnosis**1
                          					42
                          					M
                          					Dec 13
                          					Dec 26  **Options** 12/7
                                                12/14
                                                12/21
                                                12/28
                                                1/4
                                                1/11
                                                1/18
 **Exercise 4: Correct** **Case**
                                    					**Age**
                                    					**Sex**
                                    					**Date of Onset**
                                    					**Date of Diagnosis**1
                                    					42
                                    					M
                                    					Dec 13
                                    					Dec 26 The date of onset is during the week of 12/7.
 ****Exercise 4: Incorrect**** **Case**
                                    					**Age**
                                    					**Sex**
                                    					**Date of Onset**
                                    					**Date of Diagnosis**1
                                    					42
                                    					M
                                    					Dec 13
                                    					Dec 26 The date of onset is during the week of 12/7.
 **Exercise 4: Incorrect** **Case**
                                    					**Age**
                                    					**Sex**
                                    					**Date of Onset**
                                    					**Date of Diagnosis**1
                                    					42
                                    					M
                                    					Dec 13
                                    					Dec 26 The date of onset is during the week of 12/7.
 **Exercise 4: Incorrect** **Case**
                                    					**Age**
                                    					**Sex**
                                    					**Date of Onset**
                                    					**Date of Diagnosis**1
                                    					42
                                    					M
                                    					Dec 13
                                    					Dec 26 The date of onset is during the week of 12/7.
 **Exercise 4: Incorrect** **Case**
                                    					**Age**
                                    					**Sex**
                                    					**Date of Onset**
                                    					**Date of Diagnosis**1
                                    					42
                                    					M
                                    					Dec 13
                                    					Dec 26 The date of onset is during the week of 12/7.
 **Exercise 4: Incorrect** **Case**
                                    					**Age**
                                    					**Sex**
                                    					**Date of Onset**
                                    					**Date of Diagnosis**1
                                    					42
                                    					M
                                    					Dec 13
                                    					Dec 26 The date of onset is during the week of 12/7.
 **Exercise 4: Incorrect** **Case**
                                    					**Age**
                                    					**Sex**
                                    					**Date of Onset**
                                    					**Date of Diagnosis**1
                                    					42
                                    					M
                                    					Dec 13
                                    					Dec 26 The date of onset is during the week of 12/7.
 Your Turn: Exercise 5 Using the following information from a line listing, which date from the **Options** below represents the Date of Onset for Case 5? **Case**
                                    			**Age**
                                    			**Sex**
                                    			**Date of Onset**
                                    			**Date of Diagnosis**5
                          						54
                          						M
                          						Jan 9
                          						Jan 12  **Options** 12/7
                                                12/14
                                                12/21
                                                12/28
                                                1/4
                                                1/11
                                                1/18
 **Exercise 5: Incorrect** Case 5 would be plotted on the week beginning 1/4. **Case**
                                    **Age**
                                    **Sex**
                                    **Date of Onset**
                                    **Date of Diagnosis**5
                                    54
                                    M
                                    Jan 9
                                    Jan 12
 **Exercise 5: Incorrect** Case 5 would be plotted on the week beginning 1/4. **Case**
                                    **Age**
                                    **Sex**
                                    **Date of Onset**
                                    **Date of Diagnosis**5
                                    54
                                    M
                                    Jan 9
                                    Jan 12
 **Exercise 5: Incorrect** Case 5 would be plotted on the week beginning 1/4. **Case**
                                    **Age**
                                    **Sex**
                                    **Date of Onset**
                                    **Date of Diagnosis**5
                                    54
                                    M
                                    Jan 9
                                    Jan 12
 **Exercise 5: Incorrect** Case 5 would be plotted on the week beginning 1/4. **Case**
                                    **Age**
                                    **Sex**
                                    **Date of Onset**
                                    **Date of Diagnosis**5
                                    54
                                    M
                                    Jan 9
                                    Jan 12
 **Exercise 5: Correct** Case 5 would be plotted on the week beginning 1/4. **Case**
                                    **Age**
                                    **Sex**
                                    **Date of Onset**
                                    **Date of Diagnosis**5
                                    54
                                    M
                                    Jan 9
                                    Jan 12
 **Exercise 5: Incorrect** Case 5 would be plotted on the week beginning 1/4. **Case**
                                    **Age**
                                    **Sex**
                                    **Date of Onset**
                                    **Date of Diagnosis**5
                                    54
                                    M
                                    Jan 9
                                    Jan 12
 **Exercise 5: Incorrect** Case 5 would be plotted on the week beginning 1/4. **Case**
                                    **Age**
                                    **Sex**
                                    **Date of Onset**
                                    **Date of Diagnosis**5
                                    54
                                    M
                                    Jan 9
                                    Jan 12
 Summary Congratulations! You have created a basic epi curve. The completed epi curve is below. **Hepatitis A Cases by Date of Onset in Homer, Virginia,December 2011–January 2012**  To view other Quick Learns, visit CDC Learning Connection.
 Resources on Basic Epidemiology Basic Epidemiology
                            			CDC TRAIN
                            			E is for Epidemiology
                           
                            			What is Epidemiology? (00:43)
 CDC Learning Connection LogoFor more Quick-Learn lessons please visit CDC Learning Connection
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