Making an epidemic curve (epicurve)

1
Making an epidemic curve (epicurve)

• Preben Aavitsland
• (with a lot of help from Katarina Alpers, RKI)

2
The epidemic curve

• Time components of an outbreak
• Shows
• Start
• End
• Duration
• Peak
• Outliers
• Helps to form hypotheses on
• Route of transmission
• Probable exposure period
• Incubation time

3
The epidemic curve
4
The epidemic curve

• Histogram
• Area proportional to number
• No space between columns
• One population
• X-axis time
• Start before epidemic, continue after
• Interval lt 1/4 of incubation period
• Y-axis number of cases
• Usually one square one case
• Easy to make in Excel

5
Point source
No of cases
20
15
10
5
0
Time
Duration Incubation time
6
Continous source
Mean IP
7
Intermittent source
No of cases
10
9
8
7
6
5
4
3
2
1
0
1
2
3
4
5
6
7
8
9
10
11
12
13
14
15
16
17
18
19
20
21
22
Time (days)
8
Human to human transmission
No of cases
10
Generation
time
5
0
Zeit
1
2
3
4
5
6
7
8
9
10
11
12
13
14
15
16
17
18
19
20
21
22

9
Probable exposure time
No of cases
Median incubation time
(Intervall between first and last disease onset)
2
3
15
10
5
0
1
2
3
4
5
6
7
8
9
10
11
12
13
14
15
16
17
18
19
20
21
22
Time
1
50 50
Probable exposure time
Median onset time
10
Probable exposure period
No of cases
20
18
maximum incubation time
16
14
12
10
minimum incubation time
8
6
4
2
0
1
3
5
7
9
11
13
15
17
19
21
23
25
27
29
31
1
2
3
4
5
6
7
8
9
10
11
12
13
14
15
16
17
18
19
20
21
22
Time
Probable exposure period
11
Two ways of making epicurves in Excel

• The square method
• Turn a work sheet in to squares
• Fill in each patient as a square
• The chart method
• Make a table of onset times
• Use the chart wizard
• Make a histogram (by removing intervals between
  bars in a bar chart)