Towards a participatory European social contact observatory

Social contacts shape infectious disease transmission, but most contact data come from infrequent, resource-intensive stand-alone surveys that are difficult to link with longitudinal health information. Digital participatory surveillance offers an alternative for continuous collection of data requiring fewer resources. We analyzed over 110,000 contact reports from 18,000 InfluenzaNet participants, linked with sociodemographic, behavioral, and symptom data. Weighted adult age-stratified contact matrices reproduced established structural features, while temporal analyses showed that transmission-relevant patterns varied over time. Negative binomial mixed-effects models found fewer contacts among participants with influenza-like illness, particularly ILI with fever, although milder symptoms were associated with more contacts in one Dutch specification. Contacts also varied with employment, weekends, and holidays. Participatory surveillance can therefore generate valid, longitudinal contact data while integrating otherwise difficult-to-obtain participant information. This infrastructure provides a foundation for a European social contact observatory capable of providing regularly updated inputs for epidemic modeling and public health preparedness.