Josephine van Dongen

2 Acute gastroenteritis disease burden among infants with medical risk conditions 31 Results Between November 2014 and October 2017, 2500 medical risk infants met the RIVAR inclusion criteria across 13 par ticipating hospitals ( Figure 1 ). Mean gestational age was 33 weeks (SD ±4 weeks), 475 (19%) had a congenital disorder (cardiovascular 129, pulmonal 21, central nerve system 49, chromosomal 90, perinatal 70 and 199 other disorders) and 684 infants (27%) were small for gestational age. Descriptive statistics In total, 631 parents of medical risk infants consented to par ticipate. Baseline characteristics of par ticipants and non-par ticipants were comparable ( eTable 2 ). Follow up until 18 months of age was complete for 421 (67%) infants. Reasons for incomplete follow up were; dropped out (n=50), deceased (n=3) or loss to follow up (n=157) before 18 months of age. During par ticipant follow-up, 559 AGE episodes occurred. In total 275 episodes were repor ted by parents, complete information was available for 254 of those, and an additional 284 AGE episodes were retrieved from monthly questionnaires and medical records ( Figure 1 ). Pathogen distribution Of 254 AGE episodes a fecal sample was collected within 14 days of symptom onset. Of these 65 (25.6%) tested positive for norovirus and 44 (17.7%) for rotavirus. Co-infections for norovirus and rotavirus were present in four AGE episodes, 21 samples were adenovirus- and/ or astrovirus positive (8.3%). AGE episodes with a stool sample collected had a longer duration but less frequent healthcare attendance compared to those without a stool sample ( eTable 3 ). AGE disease burden The IR for all-cause AGE up to 18 months of age was 73.5 per 100 PY, IR increased with older age from 48.3 per 100 PY <6 months of age to 80.2 per 100 PY for infants 6-18 months of age ( Table 1 ). No differences were observed in IRs between subgroups of medical risk infants. The AGE IR demonstrated a clear seasonal pattern with highest rates in months January to April and October to December, eFigure 3 . Comparing the seasonal months to out-of-season months, the mean incidence was higher during seasonal months. After multiple imputation, the estimated IR for norovirus- and rotavirus positive episodes was not significantly different.