Hospitalization for lower respiratory disease during 20 yrs among under 5 yr old children in Stockholm County: a population based survey.

Lower respiratory disease (LRD) is a common cause of hospitalization in infants, and episodes of obstructive LRD increase the risk for asthma later in life. The purpose of this study was to assess time trends and geographical variation of first time hospitalization for LRD among children in Stockholm County, Sweden. Data on first time admittance for LRD among children aged up to 5 yrs from 1973 through 1992 were obtained from the Stockholm County Council hospital discharge register, and population register data were used for estimation of the population at risk. Municipal data were available for 1982-1992 on outbreaks of respiratory syncytial virus (RSV) infections and socio-economic factors. A total of 12,450 children had been hospitalized for the first time with LRD. For children aged <2 yrs a 100% increase in the rate of first time hospitalization for LRD was observed during the study period and children aged up to 1 yr predominated (50%). The average yearly increase in the population based first time hospital admission rate for LRD was 1.82%. Males constituted 65% of the cases. Of the diagnoses, 89.6% were consistent with obstructive LRD, e.g. asthma and obstructive bronchitis. In children aged up to 1 yr, peaks in the rate of hospitalization tended to coincide with outbreaks of RSV infections. Differences in hospitalization between municipalities seemed to be partly explained by differences in the admission practices of the four paediatric hospitals in the area. We conclude that the increased rate of hospitalization for lower respiratory disease in infants of Stockholm County may reflect a true increase in the incidence of obstructive respiratory disease. However, several factors determine admittance to hospital and the results need to be interpreted with caution.