Changes in epidemiology of bronchiolitis during last two decades in Finland: a register-based study

Abstract

Introduction: Bronchiolitis is one of the most common reasons for health care services use in infancy. Approximately 1-3% of infants are hospitalised annually and 6% of them need intensive care. However, the typical biannual epidemiological pattern in Nordic countries seems to have changed recently.

Aims and objectives: The aim of this study was to evaluate if the epidemiology of bronchiolitis had changed during the last two decades around Tampere, in Finland.

Methods: We collected register-based data including all infants ≤12 months of age with ICD-10 codes J21.0 (RSV bronchiolitis) or J21.99 (indeterminate bronchiolitis) that were treated in Tampere University Hospital´s paediatric ward or emergency room from 1^st January 2000 to 31^st December 2019. For analysing the incidences, we used Poisson´s regression analysis, otherwise number and percent or medians were used for describing the data. We performed analysis by SPSS Software (IBM, version 25.0).

Results: 1481 infants with bronchiolitis were hospitalised, and 99 of them were treated in the intensive care unit. Most of them (82%) were infected by RSV, the median age of infants was 84 days, 12.6% were born preterm, and the median length of stay was 3 days. We found that for the first decade, the highest incidence rate ratios (IRRs 21.3-27.8, p<0.05) were between December and March, and thereafter, highest IRRs has moved to February and March (22.6-23.7, p<0.05). The IRR (1.053; 95%CI 1.043-1.063; p<0.001) of hospitalised infants was increasing during the study period.

Conclusion: In conclusion, we found a changed pattern of bronchiolitis incidence during the last two decades; the peak was shorter and occurred later during the last decade.