1. Determinants of active participation
in internet-­‐‑based surveillance
systems
{
Daniela PaoloIi
Computational Epidemiology Laboratory
ISI Foundation, Turin, Italy
International Meeting on Emerging Disease and Surveillance
Vienna (Austria), February 15-­‐‑18 2013

2. Internet-­‐‑based platforms for infectious disease surveillance have
advantages over traditional approaches as they can potentially
recruit and monitor a wider range of subjects in a relatively
inexpensive fashion and gather information from individuals
who would not seek medical care.
Netherlands (2003)
Belgium (2003)
Portugal (2005)
Italy (2008)
United Kingdom (2009)
France (2011)
Sweden (2011)

3. The countries considered in the present
analysis had an active platform during the
influenza season 2011-­‐‑2012

4. Loss to active participation is generally a problem in cohort
studies, and it has been rarely investigated for large-­‐‑scale cross-­‐‑
country internet-­‐‑based cohort studies.
Ñ We studied the determinants of active participation of individuals in the
www.influenzanet.eu cohort during the influenza season 2011-­‐‑2012.
Ñ The web-­‐‑based national systems require volunteers to fill in a a one-­‐‑time
background survey and a weekly questionnaire about symptoms. The
background questionnaire collects socio-­‐‑demographic (gender, age,
location etc.) information on the participants, as well as information on
household composition, influenza risk status, vaccine history etc.
Ñ The symptoms questionnaire, for which a reminder is sent every week
over email, asks about respiratory symptoms, access to care, absenteeism
and utilization of medications. If no symptoms are presented, then it can
be completed in one click.

5. registration weekly reminder
questionnaire filled time windows
For the purposes of this study
id_1 ideal user active participants are defined
id_2 respondent as those that, during the 2011-­‐‑12
id_3 not enrolled influenza season, completed at
id_4
withdrawed
(i.e. lost to follow up)
least two weekly surveys within
id_5 not enrolled 60 days following their first
symptoms questionnaire.
November 2011 March 2012
data
time extraction
Country
Enrolled Volunteers
Responders to Response rate
follow-­‐‑up
Sweden
2,097
904
43%
United Kingdom
2,171
1180
54%
The Netherlands
12,514
9679
77%
Belgium
3,834
3,042
79%
France
3,540
2227
63%
Italy
1,354
657
49%
Portugal
1,152
788
68%
TOT
26662
23803
63%

6. D a t a f r o m b a c k g r o u n d
questionnaires (gender, age,
smoking behavior, education
level, vaccinatio n status,
chronic condition, household
composition) are used as
e x p l a n a t o r y v a r i a b l e s t o
predict the likelihood of
participation through odds
ratios.
Similarly to what is observed
in traditional epidemiological
studies:
s m o k i n g b e h a v i o r, l o w e r
educational level and younger
age are associated with a lower
participation.
Vaccinated users tend to
participate more as well as
users living in households
with no children or teens
younger than 18 years old. A
chronic condition doesn’t seem
t o h a v e e ff e c t o n t h e
participation or on the loss to
follow-­‐‑up.

7. At the registration, volunteers were asked a multiple-­‐‑choice
question about how they were informed about the study. The
options of the multiple-­‐‑choice question corresponded to the
different means of enrolment.
The participants answers have been rearranged in mutually
exclusive categories and each participant is counted in only one
of them.
Such categories are:
Ñ Face-­‐‑to-­‐‑face, including conferences and word of mouth
Ñ Off-­‐‑line media, including television, radio, newspapers,
leaflets and others
Ñ Online media
A multivariable logistic regression was then used to evaluate
the impact of the recruitment by different means of
information on the retention behavior.

8. OR=0.98 (0.82-­‐‑1.18)
I2=65%

9. OR=0.74 (0.54-­‐‑1.01)
I2=91%

10. Conclusions
It is possible to motivate participants sufficiently so that they
actively take part in a weekly survey over a period of several
months. Similarly to traditional epidemiological studies, smoking
behavior, educational level and age are determinants of participation
to follows-­‐‑up. An internet-­‐‑based enrollment campaign for internet-­‐‑
based epidemiological studies seems to be less effective than the off-­‐‑
line advertising in enrolling volunteers that are more likely to
participate at follow-­‐‑up questionnaires.

11. Daniela Paolo*i1, Paolo Bajardi1, Alessandro Vespignani1,4,
Sebastian Funk2, Ken Eames2, John Edmunds2, Clement Turbelin3,
Marion Debin3, Vi*oria Colizza1,3, Ronald Smallenburg5, Carl
Koppeschaar5, Sander van Noort6, Ana Franco6, Vitor Faustino6,
Gabriela Gomes6, Annasara Carnahan7, Olof Nyren7
1ISI Foundation, Turin, Italy, 2London School of Hygiene and
Tropical Medicine, 3INSERM Université Pierre et Marie Curie,
Paris, France, 4Northeastern University, Boston, USA, 5Aquisto-­‐‑
Inter BV, Amsterdam, The Netherlands, 6Instituto Gulbenkian de
Ciȇncia, Oeiras, Portugal, 7Smi*skyddsinstituet, Stockholm,
Sweden.

12. Thank you!
www.influenzanet.eu
daniela.paolobi@isi.it
References: hbp://www.influenzanet.eu/en/publications/

13. SE SE
UK UK
NL
NL
education
gender
BE
BE
FR
FR
IT
IT
PT
PT
0 20 40 60 80 100
0 20 40 60 80 100 percent
percent
no qualification secondary
male female degree still in
SE SE
vaccination against seasonal influenza
UK UK
smoking behavior
NL NL
BE BE
FR FR
IT IT
PT PT
0 20 40 60 80 100 0 20 40 60 80 100
percent percent
no yes no yes
SE SE
UK UK
chronic condition/disease
NL NL
BE BE
age
FR FR
IT PT
PT IT
0 20 40 60 80 100 0 20 40 60 80 100
percent percent
15-30 31-40 41-50 51-60 61-75 no yes
household with children and teens aged <18
SE
UK
NL
BE
FR
IT
PT
0 20 40 60 80 100
percent
no yes