Changes in risk of hospital readmission among asthmatic children in Denmark, 1978-93

BMJ 1999; 319 doi: (Published 24 July 1999) Cite this as: BMJ 1999;319:229
  1. Hans Bisgaard, professor of paediatricsa,
  2. Henrik Møller, headb
  1. a Department of Paediatrics, Rigshospitalet, National University Hospital, DK-2100 Copenhagen, Denmark
  2. b Centre for Research in Health and Social Statistics, Danish National Research Foundation, DK-2100 Copenhagen
  1. Correspondence to: Professor Bisgaard
  • Accepted 9 February 1999

The management of asthma in children has changed over the two most recent decades, with increasing emphasis on early anti-inflammatory treatment and complete disease control with inhaled steroids.1 2 We estimated the changes in hospital readmission rates for asthma in children in Denmark in 1978-93 with a view to evaluating concomitant changes in disease control.

Methods and results

Data on hospital admissions and subsequent readmissions with asthma in children aged 5-14 at first admission were obtained from the Danish National Board of Health for the period 1978-93. Readmission was defined as any subsequent admission related to asthma that was separated by 12 months or more from the first admission.

The age standardised incidence of admission to hospital for asthma was calculated by dividing the number of first admissions to hospital for asthma by the corresponding population group in the Danish population. Sequences in which a person was discharged from hospital and again admitted on the same day (as is often the case when a patient is moved from one department to another) were combined into a single admission. Age standardised rates were calculated by giving equal weights to different age groups and to the two sexes. Relative risks of readmission in different groups of patients were estimated with Cox proportional hazards regression, account being taken of sex, diagnosis at first admission, age at first admission, and period in which the first admission occurred.

The incidence of admission to hospital for asthma over the period studied was constant at roughly 1 per 1000 children per year (table) The proportional hazards regression analysis showed that the relative risk of readmission for asthma decreased gradually; in children who were first admitted to hospital for asthma in 1990-3 the estimate was 0.50, compared with 1.00 in children first admitted in 1978-81 (table). Furthermore, the mean number of days per admission decreased over the study period.

Incidence of admission to hospital for asthma, relative risk of readmission, and average number of days in hospital per admission among asthmatic children during 1978-93

View this table:


The risk of readmission for asthma in Danish children fell by half during the period from 1978 to 1993; the incidence of admission for asthma in these children was constant in this period.

The frequency of hospital admissions may be affected by at least three factors, all expected to favour an upward trend: the underlying incidence of asthma seems to have been increasing over recent decades in children in industrialised countries3 4; awareness of asthma is believed to have increased during the observation period; and a labelling shift from bronchitis to asthma has probably occurred during this period.

Because an increased incidence of new admissions to hospital for asthma was not observed, other factors must have had a moderating influence on the risk of admission. The factors favouring an increased incidence of asthma may mainly contribute mild cases of asthma, which would add little to the risk of admission to hospital and readmission. This is probably not, however, a major factor, since the relative contribution of short admissions was unchanged throughout the period The reduced risk of readmission over the study period therefore suggests that the treatment of chronic asthma has improved. The reduced length of stay in hospital for both first admissions and readmissions substantiates this interpretation of our data.

In conclusion, these data provide evidence suggesting that the management of asthma in Danish children has improved, leading to less frequent readmission and to shorter stays in hospital.


Contributors: HB and HM contributed jointly to the design, analysis, interpretation, and reporting of this study and are both guarantors for the paper.


  • Competing interests HB has been funded by major pharmaceutical companies producing antiasthma drugs, including GlaxoWellcome, Astra, Merck, and Novartis.


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