Korczyńska, Monika RobertaDalsgaard Bjerre, KDam Rasmussen, LTvenstrup Jensen, EFischer, T KBarrasa, AliciaEthelberg, S2020-11-232020-11-232020Epidemiol Infect. 2020 Feb 17;148:e52.http://hdl.handle.net/20.500.12105/11394Norovirus (NoV) infections occur very frequently yet are rarely diagnosed. In Denmark, NoV infections are not under surveillance. We aimed to collect and describe existing laboratory-based NoV data. National NoV laboratory data were collected for 2011-2018, including information on patient identification number, age and sex, requesting physician, analysis date and result. We defined positive patient-episodes by using a 30-day time window and performed descriptive and time series analysis. Diagnostic methods used were assessed through a survey. We identified 15 809 patient-episodes (11%) out of 142 648 tested patients with an increasing trend, 9366 in 2011 vs. 32 260 in 2018. This corresponded with a gradual introduction of polymerase chain reaction analysis in laboratories. The highest positivity rate was in patients aged <5 years (15%) or >85 years (17%). There was a large difference in test performance over five Danish geographical regions and a marked seasonal variation with peaks from December to February. This is the first analysis of national NoV laboratory data in Denmark. A future laboratory-based surveillance system may benefit public health measures by describing trend, burden and severity of seasons and possibly pinpoint hospital outbreaks.engVoRhttp://creativecommons.org/licenses/by/4.0/EpidemiologyNorwalk agent and related virusesHospital-acquired (nosocomial) infectionsNorovirusSurveillanceCaliciviridae InfectionsDisease OutbreaksAdolescentAdultAgedAtribución 4.0 Internacional32063241148e5210.1017/S09502688200004611469-4409Epidemiology and infectionopen access