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Table 4 Characteristics of the daily number of respiratory syndrome or influenza-like illness cases during baseline and the test period (week 36 to week 52, 2009), test statistics on the probability distribution of daily counts, the identification of day-of-the-week effects, and Poisson CUSUM parameters during individual baseline periods

From: Validity and timeliness of syndromic influenza surveillance during the autumn/winter wave of A (H1N1) influenza 2009: results of emergency medical dispatch, ambulance and emergency department data from three European regions

 

EMD-AT

EP-AT

EP-BE

ED-BE

ED-ES

Respiratory syndrome

ILI

ILI

ILI

ILI

Period

Baseline*

Test

Baseline*

Test

Baseline*

Test

Baseline*

Test

Baseline*

Test

Mean daily count

4.7

4.8

0.07

0.2

4.2

5.0

13.6

17.9

4.1

7.3

  Standard deviation

2.2

2.1

0.3

0.5

2.1

2.5

4.0

6.0

3.0

8.0

  95% Confidence Interval

4.6-4.9

4.4-5.5

0.05-0.09

0.2-0.3

3.9-4.5

4.5-5.4

13.0-14.2

16.8-19.0

3.3-4.9

5.9-8.7

Median daily count

5

5

0

0

4

5

13

18

3

5

Minimum daily count

0

1

0

0

0

1

5

5

0

0

Maximum daily count

15

12

2

2

10

14

27

34

15

36

Day-of-the-week effect

yes

 

no

 

no

 

no

 

yes

 

evaluated by Kruskal-Wallis test

p = 0.007

 

p = 0.43

 

p = 0.70

 

p = 0.19

 

p = 0.04

Mean daily count

          

  Monday

4.7

 

0.08

 

4.1

 

14.6

 

2.7

 

  Tuesday

4.4

 

0.08

 

4.0

 

12.3

 

4.9

 

  Wednesday

4.4

 

0.03

 

3.9

 

12.5

 

5.5

 

  Thursday

5.0

 

0.08

 

3.6

 

13.7

 

4.8

 

  Friday

4.5

 

0.12

 

4.8

 

14.6

 

3.4

 

  Saturday

4.7

 

0.08

 

4.3

 

13.2

 

5.5

 

  Sunday

5.4

 

0.05

 

4.6

 

14.4

 

2.0

 

Poisson CUSUM calibration $

          

no day-of-the-week variation

  

mean = 0.07

 

mean = 4.2

 

mean = 13.6

   

k = 1

 

k = 5

 

k =14

S0 = 1

 

S0 = 4

 

S0 = 10

h = 2

 

h = 7

 

h = 20

day-of-the-week variation

          

  stratum 1

Sunday

       

Sunday, Monday

 

mean = 5.4

       

mean = 2.3

 

k = 6

         

S0 = 5

       

k = 3

 

h = 10

       

S0 = 3

 
        

h = 5

 

  stratum 2

Monday-Saturday

       

Tuesday-Saturday

 

mean = 4.6

       

mean = 4.8

 

k = 5

       

k = 5

 

S0 = 4

       

S0 = 4

 
 

h = 7

       

h = 7

 
  1. *baseline = baseline period for Poisson CUSUM calibration: EMD-AT: 1/2005-12/2008 (except December to March); EP-AT: 1/2006-12/2008 (except November to March); EP-BE: 3/2009-8/2009); ED-BE: 3/2009-8/2009; ED-ES: 3/2009-8/2009.
  2. test = test period for validity and timeliness assessment; covers the autumn winter wave of pandemic A(H1N1) influenza in 2009 (week 36/2009 to week 52/2009).
  3. $Poisson CUSUM calibration: mean = baseline mean; k = reference value; S0 = head start value; h = threshold value.