Josephine van Dongen

Chapter 1 10 Epidemiology and disease burden Rotavirus is a strong seasonal pathogen with a peak incidence between January and April in temperate climates. 18,19 Since 2014 there has been an unexplained decrease in rotavirus activity in the Netherlands and possibly a transition to a biennial instead of an annual epidemic pat- tern .20,21 In 2014 and 2016 the number of rotavirus detections in the Dutch surveillance sentinel laboratories were approximately 60% lower compared to previous years. 22 During the alter- nating years 2015 and 2017 a normal rotavirus season was observed, but then 2018 and 2019 also had a normal rotavirus season. 23 In 2020, approximately half of the rotavirus detections were observed compared to the preceding year. The preventative measures (school closure and social distancing) implemented during the COVID-19 pandemic in that year potentially clarify the sharp decline in detections from April onwards. 24,25 Suggested explanations for the lower than expected rotavirus intensity in 2014 and 2016, are the mild winters, decreasing bir th rate and the implementation of universal rotavirus vaccination in the surrounding countries. 21 Despite this changing epidemiology, the yearly number of hospitalizations due to rotavirus gas- troenteritis in the Netherlands are estimated between 1900 and 3400 among children and five to six deaths occur. 26 Prematurity, small for gestational age and, presence of severe congenital pathology are risk fac- tors for a more severe and complicated rotavirus gastroenteritis. 27 This is reflected in increased hospitalization rates, prolonged hospital stay and increased mor tality compared to healthy in- fants. 27–31 In the Netherlands, rotavirus related mor tality almost exclusively occurs in this group of children. 28 Nosocomial infections in this population are par ticularly common, as these infants require prolonged (postnatal) hospitalization which predisposes them to hospital acquisition of rotavirus infection. 32 While the hospitalization and mor tality burden in this group of infants with medical risk conditions (MRC) are well defined, the community disease burden is not. Due to the self-limiting character of rotavirus disease however, the majority of cases occur outside of the hospital, 33 and this burden could therefore be substantial. Other risk-groups for severe rotavirus disease are immunocompromised patients and elder- ly. 9,18,34 About five percent of diarrhea outbreaks in geriatric care facilities are caused by rotavi- rus. 18 Up to 50% of parents experience mild to moderate complaints of gastroenteritis if their child is infected with rotavirus, indicating high transmissibility within households. 18,35 Rotavirus vaccination Based on rotavirus’ pathogenesis and immune response, elimination is not considered a realistic goal. Hygiene and sanitary measures are unable to prevent transmission. 9 Vaccination against