The Validity of Self-Initiated, Event-Driven Infectious Disease Reporting in General Population Cohorts
Figure 1
The population-based surveillance system and validation study during the influenza season 2007/2008.
Following an invitation to a randomly selected population sample at ages 0–95 years around October 1st 2007, registered cohort members were followed passively, relying on self-initiated, event-driven reporting of all colds and fevers, until May 30th 2008. Reminders were sent out at Christmas and Easter, and an end-of-follow-up questionnaire around May 30th. The validation study consisted of 2–3 randomly selected validation weeks per participant between January 14 and March 9 2008, with 1-week recall questionnaires. *Participation rate 2082/2376 (88%); another 43 were excluded due to uninterpretable reports or interference in the last week by the Easter reminder. The Easter reminder arrived when it was still possible to submit a legitimate event-driven report.