Table 1

StudyStudy designPopulationRisk factors

PICNICProspectiveInfants hospitalized for RSV infections(i) Underlying disease (CHD, CLD, immunodeficiency, multiple congenital malformations).
(ii) Postnatal age <6 weeks.
(iii) GA 33–35 weeks.

FLIPProspective case-control studyPreterm born at 33–35 weeks’ GA (risk factors for RSV-related hospitalization)(i) Chronologic age ≤ 10 weeks at the beginning of RSV epidemic season.
(ii) Breastfeeding ≤ 2 months.
(iii) ≥1 school-age siblings.
(iv) ≥4 residents or visitors at home.
(v) Family history of wheezing.

Multicenter Italian birth cohortMulticenter prospective cohort studyInfants born at 33 weeks’ GA or more(i) GA 33 + 0–37 + 6 weeks
(ii) No breastfeeding.
(iii) Presence of siblings.
(iv) Maternal smoking.
(v) Family history of atopy or wheezing.