Stable admission rate for acute asthma in Danish children since 1977

Childhood asthma is consistently reported to have increased in recent decades in most westernized countries, but it is unknown if this increase is similar across severities. We aimed to study the time-trend of acute hospital admission and readmission for asthma of school-aged children in the recent 35 years in Denmark. We analyzed time-trends in the national incidence rate of hospitalization for acute severe asthma in children aged 5-15 in Denmark during the 35-year period 1977-2012 in the Danish national registry. Only in-patient admissions with a principal diagnosis of asthma (ICD-8: 493** or ICD-10: J45** or J46**) were included. Among children with asthma hospitalizations, we investigated the risk of readmission beyond 1 month of first admission. Admissions were summarized as rates per thousand person years at risk. The overall time-trend is stable with a rate of one admission per year per thousand children at risk and a per-year incidence rate ratio 0.999 [95 % CI 0.997-1.001]. The rate of any readmission decreased from approximately 20 per thousand children in the eighties to less than 10 in the early nineties before stabilizing at around 10 per thousand children from mid-nineties and onwards. During 35 years of nation-wide follow-up, we find a highly stable incidence rate of first hospital admission for acute severe asthma in children. Moreover, rates of readmission halved during the seventies and stabilized in the last twenty years. In conclusion, our data suggest that the reported increase in childhood asthma is mainly due to less severe cases.