Surveillance Open Access
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The surveillance of persons hospitalised with COVID-19 has been essential to ensure timely and appropriate public health response. Ideally, surveillance systems should distinguish persons hospitalised with COVID-19 from those hospitalised due to COVID-19.


We compared data in two national electronic health registries in Norway to critically appraise and inform the further development of the surveillance of persons hospitalised with COVID-19.


We included hospitalised COVID-19 patients registered in the Norwegian Patient Registry (NPR) or the Norwegian Pandemic Registry (NoPaR) with admission dates between 17 February 2020 and 1 May 2022. We linked patients, identified overlapping hospitalisation periods and described the overlap between the registries. We described the prevalence of International Classification of Diseases (ICD-10) diagnosis codes and their combinations by main cause of admission (clinically assessed as COVID-19 or other), age and time.


In the study period, 19,486 admissions with laboratory-confirmed COVID-19 were registered in NoPaR and 21,035 with the corresponding ICD-10 code U07.1 in NPR. Up to late 2021, there was a 90–100% overlap between the registries, which thereafter decreased to < 75%. The prevalence of ICD-10 codes varied by reported main cause, age and time.


Changes in patient cohorts, virus characteristics and the management of COVID-19 patients from late 2021 impacted the registration of patients and coding practices in the registries. Using ICD-10 codes for the surveillance of persons hospitalised due to COVID-19 requires age- and time-specific definitions and ongoing validation to consider temporal changes in patient cohorts and virus characteristics.


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  1. Petrilli CM, Jones SA, Yang J, Rajagopalan H, O’Donnell L, Chernyak Y, et al. Factors associated with hospital admission and critical illness among 5279 people with coronavirus disease 2019 in New York City: prospective cohort study. BMJ. 2020;369:m1966.  https://doi.org/10.1136/bmj.m1966  PMID: 32444366 
  2. Ricoca Peixoto V, Vieira A, Aguiar P, Sousa P, Carvalho C, Thomas D, et al. Determinants for hospitalisations, intensive care unit admission and death among 20,293 reported COVID-19 cases in Portugal, March to April 2020. Euro Surveill. 2021;26(33):2001059.  https://doi.org/10.2807/1560-7917.ES.2021.26.33.2001059  PMID: 34414882 
  3. Feikin DR, Higdon MM, Abu-Raddad LJ, Andrews N, Araos R, Goldberg Y, et al. Duration of effectiveness of vaccines against SARS-CoV-2 infection and COVID-19 disease: results of a systematic review and meta-regression. Lancet. 2022;399(10328):924-44.  https://doi.org/10.1016/S0140-6736(22)00152-0  PMID: 35202601 
  4. Nordström P, Ballin M, Nordström A. Risk of infection, hospitalisation, and death up to 9 months after a second dose of COVID-19 vaccine: a retrospective, total population cohort study in Sweden. Lancet. 2022;399(10327):814-23.  https://doi.org/10.1016/S0140-6736(22)00089-7  PMID: 35131043 
  5. Veneti L, Bøås H, Bråthen Kristoffersen A, Stålcrantz J, Bragstad K, Hungnes O, et al. Reduced risk of hospitalisation among reported COVID-19 cases infected with the SARS-CoV-2 Omicron BA.1 variant compared with the Delta variant, Norway, December 2021 to January 2022. Euro Surveill. 2022;27(4):2200077.  https://doi.org/10.2807/1560-7917.ES.2022.27.4.2200077  PMID: 35086614 
  6. Nyberg T, Ferguson NM, Nash SG, Webster HH, Flaxman S, Andrews N, et al. Comparative analysis of the risks of hospitalisation and death associated with SARS-CoV-2 omicron (B.1.1.529) and delta (B.1.617.2) variants in England: a cohort study. Lancet. 2022;399(10332):1303-12.  https://doi.org/10.1016/S0140-6736(22)00462-7  PMID: 35305296 
  7. Bager P, Wohlfahrt J, Bhatt S, Stegger M, Legarth R, Møller CH, et al. Risk of hospitalisation associated with infection with SARS-CoV-2 omicron variant versus delta variant in Denmark: an observational cohort study. Lancet Infect Dis. 2022;22(7):967-76.  https://doi.org/10.1016/S1473-3099(22)00154-2  PMID: 35468331 
  8. Tolksdorf K, Haas W, Schuler E, Wieler LH, Schilling J, Hamouda O, et al. ICD-10 based syndromic surveillance enables robust estimation of burden of severe COVID-19 requiring hospitalization and intensive care treatment. MedRxiv. 2022.  https://doi.org/10.1101/2022.02.11.22269594 
  9. Statens Serum Institut (SSI). Opdateret klassifikation af covid-19 relaterede indlæggelser. [Updated classification of COVID-19 related hospital admissions]. Copenhagen: SSI; 2022. Danish. Available from: https://www.ssi.dk/-/media/cdn/files/fokusrapport---opdateret-definition-af-aarsag-til-indlaeggelse---10082022.pdf?la=da
  10. National Data Catalogue (Public Health Scotland). Rapid Preliminary Inpatient Data (RAPID). Edinburgh: Public Health Scotland; 2020. Available from: https://www.ndc.scot.nhs.uk/National-Datasets/data.asp?SubID=37
  11. National Board of Health and Welfare. Statistik om covid-19. [Statistics on COVID-19]. Stockholm: National Board of Health and Welfare. [Accessed: 16 Mar 2023]. Swedish. Available from: https://www.socialstyrelsen.se/statistik-och-data/statistik/statistik-om-covid-19/
  12. Klavs I, Serdt M, Učakar V, Grgič-Vitek M, Fafangel M, Mrzel M, et al. Enhanced national surveillance of severe acute respiratory infections (SARI) within COVID-19 surveillance, Slovenia, weeks 13 to 37 2021. Euro Surveill. 2021;26(42):2100937.  https://doi.org/10.2807/1560-7917.ES.2021.26.42.2100937  PMID: 34676822 
  13. Van Goethem N, Vilain A, Wyndham-Thomas C, Deblonde J, Bossuyt N, Lernout T, et al. Rapid establishment of a national surveillance of COVID-19 hospitalizations in Belgium. Arch Public Health. 2020;78(1):121.  https://doi.org/10.1186/s13690-020-00505-z  PMID: 33292566 
  14. Public Health Scotland. Why we are changing our COVID-19 reporting. Edinburgh: Public Health Scotland; 2022. Available from: https://publichealthscotland.scot/our-blog/2022/september/why-we-are-changing-our-covid-19-reporting/
  15. Norwegian Institute of Public Health (NIPH). Ukerapporter om koronavirus og covid-19. [Weekly reports on corona virus and COVID-19]. Oslo: NIPH. [Accessed: 16 Mar 2023]. Norwegian. Available from: https://www.fhi.no/publ/2020/koronavirus-ukerapporter/
  16. Helse Bergen. Norsk Pandemiregister. [Norwegian Pandemic Registry]. Bergen: Helse Bergen. [Accessed: 16 Mar 2023]. Norwegian. Available from: https://helse-bergen.no/norsk-pandemiregister
  17. Helse Bergen. Registrering i Norsk pandemiregister–informasjon til ansatte. [Registration to the Norwegian Pandemic Registry – information for employees]. Bergen: Helse Bergen. [Accessed: 31 Mar 2020. Norwegian. Available from: https://helse-bergen.no/norsk-pandemiregister/registrering-i-norsk-pandemiregister-informasjon-til-ansatte
  18. World Health Organization (WHO). International Statistical Classification of Diseases and Related Health Problems 10th Revision (ICD-10 Version:2019). Geneva: WHO; 2019. Available from: https://icd.who.int/browse10/2019/en
  19. Helsedirektoratet. Norsk pasientregister (NPR). [Norwegian Patient Registry (NPR)]. Oslo: Helsedirektoratet. [Accessed: 16 Mar 2023]. Norwegian. Available from: https://www.helsedirektoratet.no/tema/statistikk-registre-og-rapporter/helsedata-og-helseregistre/norsk-pasientregister-npr
  20. Helsedirektoratet. Forskrift om innsamling og behandling av helseopplysninger i Norsk pasientregister (Norsk pasientregisterforskriften). [Regulations on the collection and processing of health information in the Norwegian Patient Registry (Norwegian Patient Registry regulations)]. Oslo: Helsedirektoratet; 2022. Norwegian. Available from: https://lovdata.no/dokument/SF/forskrift/2007-12-07-1389
  21. The Directorate of e-health. Regler og veiledning for kliniske kodeverk i spesialisthelsetjenesten (ICD-10, NCSP, NCMP og NCRP). [Rules and guidance for clinical coding systems in specialist healthcare (ICD-10, NCSP, NCMP and NCRP]. Oslo: the Directorate of eHealth. [Accessed: 16 Mar 2023]. Norwegian. Available from: https://www.ehelse.no/kodeverk-terminologi/regler-og-veiledning-for-kliniske-kodeverk-i-spesialisthelsetjenesten-icd-10-ncsp-ncmp-og-ncrp
  22. Norwegian Institute of Public Health (NIPH). Elektronisk laboratoriemelding til MSIS og laboratoriedatabasen. [Electronic laboratory report to MSIS and the laboratory database]. Oslo: NIPH; 2022. Norwegian. Available from: https://www.fhi.no/hn/helseregistre-og-registre/msis/elektronisk-laboratoriemelding-til-msis-og-laboratoriedatabasen/
  23. The Norwegian Tax Administration. National Population Register. Oslo: The Norwegian Tax Administration. [Accessed: 16 Mar 2023]. Available from: https://www.skatteetaten.no/en/person/national-registry/
  24. Norwegian Institute of Public Health (NIPH). Emergency preparedness register for COVID-19 (Beredt C19). Oslo: NIPH; 2022. Available from: https://www.fhi.no/en/id/infectious-diseases/coronavirus/emergency-preparedness-register-for-covid-19/
  25. European Centre for Disease Prevention and Control (ECDC). Operational considerations for respiratory virus surveillance in Europe. Stockholm: ECDC; 2022. Available from: https://www.ecdc.europa.eu/en/publications-data/operational-considerations-respiratory-virus-surveillance-europe
  26. Hahsler M, Buchta C, Gruen B, Hornik K. (2022). arules: Mining Association Rules and Frequent Itemsets. R package version 1.7-5. 2022. [Accessed: 16 Mar 2023]. Available from: https://CRAN.R-project.org/package=arules
  27. R Core Team. R: A language and environment for statistical computing. Vienna: R Foundation for Statistical Computing; 2020. Available from: https://www.R-project.org
  28. Wu G, D’Souza AG, Quan H, Southern DA, Youngson E, Williamson T, et al. Validity of ICD-10 codes for COVID-19 patients with hospital admissions or ED visits in Canada: a retrospective cohort study. BMJ Open. 2022;12(1):e057838.  https://doi.org/10.1136/bmjopen-2021-057838  PMID: 35063962 
  29. Bodilsen J, Leth S, Nielsen SL, Holler JG, Benfield T, Omland LH. Positive predictive value of ICD-10 diagnosis codes for COVID-19. Clin Epidemiol. 2021;13:367-72.  https://doi.org/10.2147/CLEP.S309840  PMID: 34079379 
  30. Lynch KE, Viernes B, Gatsby E, DuVall SL, Jones BE, Box TL, et al. Positive predictive value of COVID-19 ICD-10 diagnosis codes across calendar time and clinical setting. Clin Epidemiol. 2021;13:1011-8.  https://doi.org/10.2147/CLEP.S335621  PMID: 34737645 
  31. Kadri SS, Gundrum J, Warner S, Cao Z, Babiker A, Klompas M, et al. Uptake and accuracy of the diagnosis code for COVID-19 among US hospitalizations. JAMA. 2020;324(24):2553-4.  https://doi.org/10.1001/jama.2020.20323  PMID: 33351033 
  32. Public Health Scotland. Public Health Scotland COVID-19 Statistical Report, as at 22 August 2022. Edinburgh: Public Health Scotland; 2022. Available from: https://publichealthscotland.scot/publications/covid-19-statistical-report/covid-19-statistical-report-24-august-2022/
  33. Seo WJ, Kang J, Kang HK, Park SH, Koo HK, Park HK, et al. Impact of prior vaccination on clinical outcomes of patients with COVID-19. Emerg Microbes Infect. 2022;11(1):1316-24.  https://doi.org/10.1080/22221751.2022.2069516  PMID: 35465831 
  34. Lee JE, Hwang M, Kim YH, Chung MJ, Sim BH, Chae KJ, et al. Imaging and clinical features of COVID-19 breakthrough infections: a multicenter study. Radiology. 2022;303(3):682-92.  https://doi.org/10.1148/radiol.213072  PMID: 35103535 
  35. Stepanova M, Lam B, Younossi E, Felix S, Ziayee M, Price J, et al. The impact of variants and vaccination on the mortality and resource utilization of hospitalized patients with COVID-19. BMC Infect Dis. 2022;22(1):702.  https://doi.org/10.1186/s12879-022-07657-z  PMID: 35996076 
  36. Martin B, DeWitt PE, Russell S, Sanchez-Pinto LN, Haendel MA, Moffitt R, et al. Acute upper airway disease in children with the Omicron (B.1.1.529) variant of SARS-CoV-2-a report from the US National COVID Cohort Collaborative. JAMA Pediatr. 2022;176(8):819-21.  https://doi.org/10.1001/jamapediatrics.2022.1110  PMID: 35426941 
  37. European Commission (EC). Annex to the Commission implementing decision on the financing of the Programme for the Union’s action in the field of health (‘EU4Health Programme’) and the adoption of the work programme for 2023. Brussels: EC; 2022. Available from: https://health.ec.europa.eu/system/files/2022-11/wp2023_annex_en.pdf
  38. The Norwegian Government. Tidslinje: myndighetenes håndtering av koronasituasjonen. [Timeline: news from Norwegian Ministries about the corona virus disease Covid-19]. Oslo: the Norwegian Government. [Accessed: 16 Mar 2023]. Norwegian. Available from: https://www.regjeringen.no/no/tema/Koronasituasjonen/tidslinje-koronaviruset/id2692402/

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