Assessment of personal factors
For both EGEA1 and EGEA2 surveys, participants underwent a clinical visit and responded to a detailed questionnaire, based on international standardized tools (16). Potential personal determinants tested in the present study were: age at the time of IgG assessment, sex, BMI at the time of IgG assessment and passive and active tobacco smoke. Moreover, season of blood sampling (from which IgG responses to respiratory virus were measured) was also considered (“January-March”, “April-June”, “July-September” and “October-December”) because there is good evidence for seasonal differences regarding respiratory virus infections (17,18). In EGEA1, children were considered as exposed to passive smoking if they lived with at least one parent who was an active smoker at the time of the study. In EGEA2, adults were defined as “never smoker”, “former smoker” (daily smoker who stopped smoking for at least 1 month before the survey) or “active smoker” (current smoker of cigarettes, pipes, cigarillos or cigars at the time of the survey).