Paediatric hospitalizations due to allergic reactions increasing in Finland and decreasing in Sweden
Authors: Lasse Saarimäki, Sandra Ekström, Jennifer L. P. Protudjer, Heini Huhtala, Jussi Karjalainen, Inger Kull, Juho E. Kivistö
Journal: Allergy (2024)

Increases in severe allergic reactions have been documented among children and adults,1-3 but recent trajectories remain unclear. In the last decade, studies4, 5 have provided evidence that earlier introduction of allergenic foods to infants may reduce the risk of allergy. The primary aim of this study was therefore to investigate the incidence of hospitalizations due to allergic reactions in children aged 0–19 years in Finland and Sweden between 2012 and 2020. The secondary aim was to report trends in outpatient visits among children due to anaphylaxis, and prescribed adrenalin auto-injector (AAI) dispensing in both countries. The study was based on data from national registries in Finland and Sweden, for the entire paediatric populations aged 0–19 years. For hospitalizations, the International Classification of Diseases 10th Revision codes included were T78.0–T78.4. For outpatient visits, only anaphylaxis (T78.0 and T78.2) was included. AAI dispensing data were obtained from open databases. For more information about materials and methods, see the Appendix S1. Between 2012 and 2020, there was a cumulative observation time of 10,705,578 person-years (PY) in Finland and 20,642,565 PY in Sweden. There were 2250 children hospitalized for severe allergic reactions in Finland and 4474 in Sweden. The mean incidence rates (IRs) were 21.41 and 21.85 per 100,000 PY, respectively. Over time, the IRs for hospitalization increased by 29% in Finland, from 18.34 to 23.71, and decreased by 43% in Sweden, from 28.66 to 16.33 (Figure 1). Regarding anaphylaxis only, there were 5187 cases in Finland (of which 1277 [24.6%] were hospitalizations and 3910 [73.4%] were visits). Over the study period, there was an increase in incidence by 120% (2012: IR 32.61, 2020: IR 71.72). The increase was seen for both hospitalizations and visits. In Sweden, there were 7095 cases (2669 [37.6%] hospitalizations, 4426 [62.4%] visits), with a 24% increase in incidence (2012: IR 29.35; 2020: 36.33). In Sweden, hospitalizations decreased (incidence rate ratio IRR 0.95 [0.94–0.96]) and visits increased (IRR 1.08 [1.07–1.09], Figure 2). Hospitalizations and visits for anaphylaxis were most common among children aged 0–4 years in both Finland and Sweden, with cases numbering 2429 (39.4% of all cases) and 2953 (33.2%), respectively. In Finland, this was the only age group in which hospitalizations clearly increased, with an IR change from 32.05 to 56.06, corresponding to a 74.9% increase (Figure S1). Results from sub-group analyses and by different diagnosis codes are presented in the Appendix S1. In total, there were 78,141 unique AAI dispensing for the study population in Finland and 105,456 in Sweden. An increase of 32% in dispensed AAIs was seen in Finland (IR 2012: 6.36; 2020: 8.37), whereas a stable trend was seen in Sweden (IR 2012: 5.00; 2020: 4.80). The main strength of the study is the use of national data set capturing hospital admissions. However, the study also has some limitations. Although we used ICD codes, which are international, allergic reactions may be coded differently in Finland and Sweden, and there may have been misdiagnoses and/or miscoding.6 As regards visits, it is possible that an individual had more than one visit due to the same allergic reaction, for example, first in emergency care and later in an outpatient setting. We can only speculate about the reasons for the different trends in Finland and Sweden. To our knowledge, there have not been any local changes in coding of severe allergic reactions or anaphylaxis. From the observed results, it seems that the Finnish Allergy programme has not decreased the number of hospitalizations, although some of the increased visits may be due to an increase in awareness during this period. In conclusion, hospitalizations due to allergic reactions increased in Finland from 2012 to 2020, whereas they decreased in Sweden. The overall incidence of severe allergic reactions increased more in Finland than in Sweden. The incidence rate of anaphylaxis in Finland is now higher than that in Sweden, where a shift from hospitalizations to outpatient visits was observed. The incidence increased in particular among 0- to 4-year-old Finnish children. Lasse Saarimäki: Planning the study, designing the methodology, collecting data, performing statistical analyses, writing the article and being responsible for the publication process. Sandra Ekström: Planning the study, designing the methodology, collecting data, performing statistical analyses and writing the article. Juho E. Kivisto: Planning the study, designing the methodology and writing the article. Inger Kull: Planning the study, designing the methodology and writing the article. Heini Huhtala: Performing statistical analyses and writing the article. Jennifer L. P. Protudjer: Writing the article and providing expertise in processing results. Jussi Karjalainen: Planning the study, designing the methodology and writing the article. The study was funded by the Konsul Th C Bergh Foundation and Hesselmans Foundation. JLP Protudjer is Section Head, Allied Health and Co-Lead, Research Pillar for the Canadian Society of Allergy and Clinical Immunology and is on the steering committee for Canada's National Food Allergy Action Plan. She reports consulting for Ajonomoto Cambrooke, Novartis, Nutricia and ALK Abelló. Other authors have no conflicts of interest relevant to this article to disclose. The data that support the findings of this study are available from the corresponding author upon reasonable request. Appendix S1 Please note: The publisher is not responsible for the content or functionality of any supporting information supplied by the authors. Any queries (other than missing content) should be directed to the corresponding author for the article.