Participation and population
During the 2014-2015 season, 3,905 (59%) of the 6,632 GrippeNet.fr registered individuals were considered active and were included in the study; 4,906 (75%) of 6,515 in 2015-2016; and 5,164 (83%) of 6,234 in 2016-2017 (Table 1). Overall they were 13,974 participants included in the study over the three seasons, and among them 3,152 individuals were included to the study for the three seasons. During the study period, 385 participants (9.9%) declared at least one AGE in 2014-2015, 412 (8.4%) in 2015-2016 and 311 (6%) in 2016-2017. Mean number of AGE episode per participant are described in Table 1.
Table 1 Description of the number of participants included in the study and the number of AGE cases reported per season, using the AGE definition of the French Sentinelles network
|
Season
2014-2015
|
Season
2015-2016
|
Season
2016-2017
|
GrippeNet.fr registered individuals*, n
|
6,632
|
6,515
|
6,234
|
Active participants included in the study**, n (%)
|
3,905 (59%)
|
4,906 (75%)
|
5,164 (83%)
|
Weekly surveys filled by active participants, n
|
75,576
|
100,147
|
82,793
|
AGE episode reported, n
|
439
|
476
|
336
|
Participants having at least one AGE episode, n (%)
|
385 (9.9%)
|
412 (8.4%)
|
311 (6.0%)
|
Mean number of AGE episode per participant having at least one (min – max)
|
1.14 (1 – 5)
|
1.16 (1 – 5)
|
1.08 (1 – 4)
|
Mean number of AGE episode per participant
|
0.112
|
0.097
|
0.065
|
*Any GrippeNet.fr participants having filled at least one preliminary survey
**GrippeNet.fr participants having filled at least three weekly surveys (one before, one during and one after the AGE epidemic period for the first two seasons, and one during and one after for the last season)
Socio-demographic characteristics, exposure and health status were similar for the three seasons (Table 2). The participants were mostly women, 60% in each season (n=2,326 in the first one, n=2,942 in the second and n=3,113 in the third), they lived in urban area for 81% of them (according to the season, n=3,145, n=3,973 and n=4,161) and were on average 53 years old in the first season, 53.6 in the second and 53 in the third. Almost half of the participants had at least one social exposure: 10% to 11% with patients, n=388 in the first season, n=476 the second, n=555 in the third, 10% with elderly, n=401, n=486 and n=537), 31% to 32% with a group of people, n=1,230, n=1,533 and n=1677) or 24% to 33% with children, n=952, n=1,213 and n=1,223). Concerning health status, 811 participants (21%) of the first season, 1,079 (22%) of the second and 1,098 (21%) of the third season were treated for at least one comorbidity.
Table 2 Socio-demographic characteristics, exposure and health characteristics of participants of the study according to the season
Variables
|
Season
2014-2015
n (%)
|
Season
2015-2016
n (%)
|
Season
2016-2017
n (%)
|
|
|
|
|
Socio-demographic characteristics
|
|
Gender (m.d. = 0)
Female
Male
|
2,326 (60%)
1,579 (40%)
|
2,942 (60%)
1,964 (40%)
|
3,113 (60%)
2,051 (40%)
|
Age (m.d. = 18)
[0-10[
[10-15[
[15-60[
> 60
|
98 (3%)
104 (3%)
1,970 (50%)
1,732 (44%)
|
188 (4%)
128 (3%)
2,541 (52%)
2,042 (42%)
|
175 (3%)
115 (2%)
2,660 (52%)
2,205 (43%)
|
Household composition (m.d. =49)
Living alone
Living with ≥1 child
Living with adults only
|
614 (16%)
1,219 (31%)
2,059 (53%)
|
765 (16%)
1,590 (33%)
2,532 (52%)
|
838 (16%)
1,634 (32%)
2,675 (52%)
|
Main activity (m.d. = 258)
Working
Student
Unemployed
Retired
Stay at home/Sick leave
|
1,822 (48%)
344 (9%)
109 (3%)
1,411 (37%)
148 (4%)
|
2,320 (48%)
487 (10%)
133 (3%)
1,702 (35%)
171 (4%)
|
2,453 (48%)
456 (9%)
128 (3%)
1,846 (36%)
187 (4%)
|
Level of education (m.d. = 90)
Middle school diploma
High school diploma
Higher education
Not concerned*
|
613 (16%)
696 (18%)
2,223 (57%)
336 (9%)
|
707 (15%)
861 (18%)
2,807 (58%)
498 (10%)
|
814 (16%)
944 (18%)
3,043 (59%)
343 (7%)
|
Place of residency (m.d. = 0)
Urbain
Rural
|
3,145 (81%)
760 (19%)
|
3,973 (81%)
933 (19%)
|
4,161 (81%)
1,003 (19%)
|
Exposure
|
|
Use of public transportation (m.d. = 0)
Yes
No
|
605 (15%)
3,300 (85%)
|
770 (16%)
4,136 (84%)
|
813 (16%)
4,351 (84%)
|
Contacts (m.d. = 0)
Contact with patients
Contact with elderly
Contact with a group of people (≥10)
Contact with children
|
388 (10%)
401 (10%)
1,230 (31%)
952 (24%)
|
476 (10%)
486 (10%)
1,533 (31%)
1,213 (25%)
|
555 (11%)
537 (10%)
1,677 (32%)
1223 (24%)
|
Pets at home (m.d. = 22)
None
At least one
|
2,127 (55%)
1,774 (45%)
|
2,711 (55%)
2,187 (45%)
|
2,851 (55%)
2,303 (45%)
|
Health characteristics
|
|
Common colds frequency (m.d. = 358)
Never
Rare
Often
|
1,749 (45%)
1,401 (36%)
698 (18%)
|
2,079 (44%)
1,740 (37%)
898 (19%)
|
2,248 (44%)
1,890 (37%)
914 (18%)
|
Smoking status (m.d. = 16)
Non smoker
Smoker
|
3,492 (90%)
406 (10%)
|
4,377 (89%)
525 (11%)
|
4,597 (89%)
562 (11%)
|
Comorbidities (m.d. = 0)
No comorbidities
At least one comorbidity**
Treated asthma
Treated diabetes
Treated heart condition
Treated kidney condition
Treated immunosuppression
Treated pulmonary condition
|
3,094 (79%)
811 (21%)
219 (6%)
139 (4%)
397 (10%)
22 (1%)
109 (3%)
102 (3%)
|
3,827 (78%)
1,079 (22%)
319 (7%)
184 (4%)
501 (10%)
36 (1%)
144 (3%)
139 (3%)
|
4,066 (79%)
1,098 (21%)
303 (6%)
203 (4%)
502 (10%)
29 (1%)
133 (3%)
124 (2%)
|
Respiratory allergy (m.d. = 0)
None
At least one
|
2,609 (67%)
1,296 (33%)
|
3,267 (67%)
1,639 (33%)
|
3,378 (65%)
1,786 (35%)
|
Pregnancy (m.d. = 67)
Yes
No
Not concerned***
|
39 (1%)
660 (17%)
3,191 (82%)
|
56 (1%)
871 (18%)
3,943 (81%)
|
50 (1%)
962 (19%)
4,136 (80%)
|
BMI (m.d. = 229)
Underweight (<18.5)
Normal weight ([18.5 – 25[)
Overweight ([25 – 30[)
Obese (>30)
|
185 (5%)
2,208 (57%)
1,027 (27%)
424 (11%)
|
207 (4%)
2791(58%)
1,292 (27%)
526 (11%)
|
231 (5%)
2,911 (57%)
1,368 (27%)
576 (11%)
|
m.d. = missing data. The number correspond to the total of missing data for both seasons
*Children and students not having finished their studies
**Participants having responded they are taking medication for at least one of the condition listed below
***Women under 15 or above 55 and men
Risk factor analysis
With univariable analysis (Table 3), we identify several factors associated with the risk of having at least one AGE during a winter season (p<0.05): season, age, household composition, main activity, having pets, common cold or flu-like disease frequency, being treated for at least one chronic condition, having a respiratory allergy, and BMI.
Regarding adjusted Odds Ratio (aOR) from the final multivariable model (table 3), compared to individuals between 15 and 60 yo, elderly (≥ 60 yo) tend to have fewer AGE episodes (aOR=0.76, 95% CI [0.64 ; 0.89]), as children between 10 and 15 y (aOR=0.60 [0.37;0.98]). Having pets at home is associated with having AGE episode (aOR=1.23 [1.08 ; 1.41]). Living alone is also associated with having AGE episode (aOR=1.31 [1.09 ; 1.59]) compared to people living with adults. We also highlight three health characteristics associated with AGE: overweight (aOR=1.25 [1.07;1.45]) and obesity (aOR=1.47 [1.19;1.81]) compared to normal BMI, having often (aOR=1.63 [1.37;1.94]) or rarely (aOR=1.17 [1.01;1.36]) common cold or flu-like disease compared to never, and being treated for at least one chronic condition (aOR=1.35 [1.16;1.58]. Participants were less likely to have AGE during the 2015/16 season (aOR=0.84 [0.73 ; 0.97]) and the 2016/17 season (aOR=0.56 [0.48 ; 0.65] compared to the 2014/15 season.
Table 3 Factors associated with having at least one AGE episode during a winter season (univariate and multivariate analysis) among the 8,811 participants-season, using the AGE definition of the French Sentinelles network
|
|
|
|
univariate analysis
|
multivariate analysis
|
Variable
|
|
N*
|
Case
N (%)
|
OR [IC 95%]
|
p-value
|
OR [IC 95%]
|
p-value
|
Season
|
2014-2015
2015-2016
2016-2017
|
3,905
4,906
5,164
|
385 (10%)
412 (8%)
311 (6%)
|
-
0.83 [0.72 – 0.95]
0.58 [0.50 – 0.67]
|
<0.001
|
-
0.84 [0.73 – 0.97]
0.56 [0.48 – 0.65]
|
<0.001
|
Sociodemographic characteristics
|
|
|
Gender
|
Female
Male
|
8,381
5,594
|
663 (8%)
445 (8%)
|
-
1.01 [0.88 – 1.15]
|
0.890
|
|
|
Age (years)
|
15 to 59
< 10
10 to 14
≥ 60
|
7,171
461
347
5,978
|
617 (9%)
54 (12%)
16 (5%)
420 (7%)
|
-
1.42 [1.04 – 1.93]
0.52 [0.32 – 0.84]
0.80 [0.70 – 0.92]
|
<0.001
|
-
1.26 [0.86 – 1.85]
0.60 [0.37 – 0.98]
0.76 [0.64 – 0.89]
|
<0.001
|
Household composition
|
Living with adults only
Living alone
Living with ≥1 child
|
7,266
2,217
4,443
|
536 (7%)
208 (9%)
361 (8%)
|
-
1.28 [1.07 – 1.54]
1.10 [0.95 – 1.28]
|
0.023
|
-
1.31 [1.09 – 1.59]
0.98 [0.82 – 1.17]
|
0.015
|
Main activity
|
Working
Student
Unemployed
Retired
Stay at home/Sick leave
|
6,595
1,287
370
4,959
506
|
573 (9%)
91 (7%)
34 (9%)
343 (7%)
36 (7%)
|
-
0.79 [0.62 – 1.01]
1.07 [0.72 – 1.60]
0.77 [0.67 – 0.90]
0.82 [0.56 – 1.20]
|
0.009
|
|
|
Level of education
|
High school diploma
Middle school diploma
Higher education
Not concerned
|
2,564
2,211
7,488
961
|
211 (8%)
157 (7%)
661 (8%)
77 (8%)
|
-
0.86 [0.68 – 1.09]
0.99 [0.83 – 1.18]
0.99 [0.74 – 1.31]
|
0.545
|
|
|
Place of residency
|
Rural
Urban
|
2,696
11,279
|
198 (7%)
910 (8%)
|
-
1.10 [0.93 – 1.30]
|
0.269
|
|
|
Exposure
|
|
|
|
|
|
|
|
Use of public transportation
|
No
Yes
|
11,787
2,188
|
937 (8%)
171 (8%)
|
-
0.99 [0.83 – 1.18]
|
0.876
|
|
|
Pets at home
|
None
At least one
|
7,689
6,264
|
552 (7%)
555 (9%)
|
-
1.26 [1.11 – 1.43]
|
<0.001
|
-
1.23 [1.08 – 1.41]
|
<0.001
|
Contact with patients
|
No
Yes
|
12,556
1,424
|
978 (8%)
130 (9%)
|
-
1.19 [0.98 – 1.44]
|
0.083
|
|
|
Contact with elderly
|
No
Yes
|
12,551
1,424
|
994 (8%)
114 (8%)
|
-
1.00 [0.81 – 1.23]
|
0.992
|
|
|
Contact with a group of people
|
No
Yes
|
9,535
4,440
|
730 (8%)
378 (9%)
|
-
1.12 [0.98 – 1.28]
|
0.092
|
|
|
Contact with children
|
No
Yes
|
10,587
3,388
|
855 (8%)
253 (7%)
|
-
0.93 [0.80 – 1.08]
|
0.325
|
|
|
Health characteristics
|
Common cold frequency
|
Never
Rare
Often
|
6,076
5,031
2,510
|
399 (7%)
399 (8%)
287 (11%)
|
-
1.21 [1.04 – 1.40]
1.79 [1.52 – 2.11]
|
<0.001
|
-
1.17 [1.01 – 1.36]
1.63 [1.37 – 1.94]
|
<0.001
|
Smoking status
|
Non smoker
Smoker
|
12,466
1,493
|
973 (8%)
133 (9%)
|
-
1.15 [0.94 – 1.41]
|
0.178
|
|
|
Comorbidities**
|
No comorbidities
At least one comorbidity
Treated asthma
Treated diabetes
Treated heart condition
Treated kidney condition
Treated immunosuppression
Treated pulmonary condition
|
10,987
2,988
841
526
1400
87
386
365
|
810 (7%)
298 (10%)
88 (10%)
61 (12%)
133 (10%)
5 (6%)
48 (12%)
34 (9%)
|
-
1.38 [1.19 – 1.60]
1.37 [1.07 – 1.75]
1.53 [1.10 – 2.12]
1.26 [1.04 – 1.53]
0.69 [0.29 – 1.64]
1.67 [1.20 – 2.32]
1.17 [0.82 – 1.69]
|
<0.001
0.012
0.011
0.021
0.396
0.023
0.414
|
-
1.35 [1.16 – 1.58]
|
<0.001
|
Respiratory allergy
|
None
At least one
|
9,254
4,721
|
689 (7%)
419 (9%)
|
-
1.20 [1.05 – 1.37]
|
0.008
|
|
|
BMI
|
Normal weight (18.5 to 24[)
Underweight (< 18.5)
Overweight (25 to 29)
Obese (≥ 30)
|
6,923
1,126
3,340
1,347
|
560 (7%)
37 (6%)
318 (9%)
171 (11%)
|
-
0.84 [0.59 – 1.18]
1.23 [1.05 – 1.43]
1.63 [1.33 – 1.99]
|
<0.001
|
-
0.72 [0.50 – 1.02]
1.25 [1.07 – 1.45]
1.47 [1.19 – 1.81]
|
<0.001
|
|
|
|
|
|
|
|
|
|
**We only include the gathered variable “At least one comorbidity” in the final model, none of the individual one listed below
Complementary analysis
Using the alternate WHO AGE definition (Table 4), 574 (14.7%) participants had at least one AGE episode in the 2014-2015 season, 682 (13.9%) in 2015-2016 and 568 (11.0%) in 2016-2017. In the final multivariable model, factors associated with at least one AGE episode per season using the previous definition were still significant (table 4). We identified three additional risk factors: men had less AGE episodes than women (aOR=0.81 [0.72; 0.91]), people with a lower level of education (middle school diploma) tend to have more episodes than people with high school diploma (aOR=0.78 [0.64 ; 0.95]), a history of respiratory allergy was associated with AGE (aOR=1.20 [1.07 ; 1.35]).
Table 4 Factors associated with having at least one AGE episode during a winter season (univariate and multivariate analysis) among the 8,811 participants-season, using the AGE definition of the WHO expert group
|
|
|
|
univariate analysis
|
multivariate analysis
|
Variable
|
|
N*
|
Case
N (%)
|
OR [IC 95%]
|
p-value
|
OR [IC 95%]
|
p-value
|
Season
|
2014-2015
2015-2016
2016-2017
|
3,905
4,906
5,164
|
574 (15%)
682 (14%)
568 (11%)
|
-
0.92 [0.82 – 1.03]
0.71 [0.63 – 0.80]
|
<0.001
|
-
0.92 [0.82 – 1.04]
0.68 [0.60 – 0.78]
|
<0.001
|
Sociodemographic characteristics
|
|
|
Gender
|
Female
Male
|
8,381
5,594
|
1,168 (14%)
656 (12%)
|
-
0.82 [0.74 – 0.92]
|
<0.001
|
-
0.81 [0.72 – 0.91]
|
<0.001
|
Age (years)
|
15 to 59
< 10
10 to 14
≥ 60
|
7,171
461
347
5,978
|
1,018 (14%)
146 (32%)
60 (17%)
596 (10%)
|
-
2.82 [2.27 – 3.51]
1.26 [0.93 – 1.71]
0.67 [0.59 – 0.75]
|
<0.001
|
-
2.33 [1.35 – 4.02]
1.09 [0.60 – 1.95]
0.70 [0.61 – 0.80]
|
<0.001
|
Household composition
|
Living with adults only
Living alone
Living with ≥1 child
|
7,266
2,217
4,443
|
833 (11%)
309 (14%)
675 (15%)
|
-
1.22 [1.05 – 1.43]
1.37 [1.22 – 1.53]
|
<0.001
|
-
1.20 [1.03 – 1.41]
0.95 [0.83 – 1.10]
|
0.052
|
Main activity
|
Working
Student
Unemployed
Retired
Stay at home/Sick leave
|
6,595
1,287
370
4,959
506
|
905 (14%)
262 (20%)
53 (14%)
494 (10%)
56 (11%)
|
-
1.61 [1.37 – 1.89]
1.03 [0.75 – 1.42]
0.69 [0.61 – 0.78]
0.79 [0.58 – 1.07]
|
<0.001
|
|
|
Level of education
|
High school diploma
Middle school diploma
Higher education
Not concerned
|
2,564
2,211
7,488
961
|
316 (12%)
221 (10%)
1,048 (13%)
228 (24%)
|
-
0.80 [0.66 – 0.97]
1.05 [0.91 – 1.22]
2.23 [1.82 – 2.74]
|
<0.001
|
-
0.78 [0.64 – 0.95]
1.00 [0.86 – 1.16]
1.19 [0.71 – 1.99]
|
0.031
|
Place of residency
|
Rural
Urban
|
2,696
11,279
|
360 (13%)
1,464 (13%)
|
-
0.97 [0.85 – 1.10]
|
0.605
|
|
|
Exposure
|
|
|
|
|
|
|
|
Use of public transportation
|
No
Yes
|
11,787
2,188
|
1,450 (13%)
284 (13%)
|
-
0.98 [0.85 – 1.13]
|
0.815
|
|
|
Pets at home
|
None
At least one
|
7,689
6,264
|
933 (12%)
889 (14%)
|
-
1.20 [1.08 – 1.33]
|
<0.001
|
-
1.18 [1.06 – 1.32]
|
0.009
|
Contact with patients
|
No
Yes
|
12,556
1,424
|
1,603 (13%)
221 (16%)
|
-
1.26 [1.08 – 1.48]
|
0.003
|
|
|
Contact with elderly
|
No
Yes
|
12,551
1,424
|
1,653 (13%)
171 (12%)
|
-
0.90 [0.76 – 1.07]
|
0.226
|
|
|
Contact with a group of people
|
No
Yes
|
9,535
4,440
|
1,212 (13%)
612 (14%)
|
-
1.10 [0.99 – 1.22]
|
0.091
|
|
|
Contact with children
|
No
Yes
|
10,587
3,388
|
1,489 (12%)
335 (16%)
|
-
1.33 [1.18 – 1.49]
|
<0.001
|
|
|
Health characteristics
|
Common cold frequency
|
Never
Rare
Often
|
6,076
5,031
2,510
|
634 (10%)
652 (13%)
500 (20%)
|
-
1.24 [1.10 – 1.39]
2.05 [1.79 – 2.34]
|
<0.001
|
-
1.14 [1.01 – 1.29]
1.58 [1.37 – 1.82]
|
<0.001
|
Smoking status
|
Non smoker
Smoker
|
12,466
1,493
|
1,624 (13%)
198 (13%)
|
-
1.02 [0.86 – 1.20]
|
0.860
|
|
|
Comorbidities**
|
No comorbidities
At least one comorbidity
Treated asthma
Treated diabetes
Treated heart condition
Treated kidney condition
Treated immunosuppression
Treated pulmonary condition
|
10,987
2,988
841
526
1400
87
386
365
|
1,407 (13 %)
417 (14%)
138 (16%)
75 (14%)
172 (12%)
9 (10%)
68 (18%)
52 (14%)
|
-
1.10 [0.97 – 1.25]
1.32 [1.08 – 1.62]
1.10 [0.83 – 1.46]
0.94 [0.79 – 1.12]
0.73 [0.33 – 1.59]
1.43 [1.07 – 1.91]
1.08 [0.80 – 1.45]
|
0.136
0.008
0.508
0.522
0.425
0.017
0.633
|
-
1.18 [1.03 – 1.36]
|
0.004
|
Respiratory allergy
|
None
At least one
|
9,254
4,721
|
1,131 (12%)
693 (15%)
|
-
1.23 [1.10 – 1.37]
|
<0.001
|
-
1.20 [1.07 – 1.35]
|
<0.001
|
BMI
|
Normal weight (18.5 to 24[)
Underweight (< 18.5)
Overweight (25 to 29)
Obese (≥ 30)
|
6,923
1,126
3,340
1,347
|
976 (12%)
93 (15%)
459 (12%)
240 (16%)
|
-
1.26 [1.00 – 1.60]
1.00 [0.88 – 1.14]
1.30 [1.10 – 1.54]
|
0.005
|
-
0.99 [0.77 – 1.26]
1.16 [1.02 – 1.33]
1.35 [1.13 – 1.61]
|
<0.001
|
**We only include the gathered variable “At least one comorbidity” in the final model, none of the individual one listed below