The results suggest that exposure to combustion products containing NO2 may be of particular importance for the development of wheezing bronchitis in girls.

A population-based case-control study was performed to investigate etiologic factors for wheezing bronchitis and asthma in children up to four years of age. A total of 199 children hospitalized for the first time with these diagnoses at a major hospital in Stockholm in 1986-1988 constituted the cases, 351 children from the catchment area of the hospital were used as controls. Information on known and suspected risk factors was obtained through home interviews with a parent. Parental smoking was associated with a relative risk of 1.8 (95% confidence interval 1.3-2.6) corresponding to a population attributable proportion of 27%. The strongest association was seen for maternal smoking and children below 18 months of age. Other major risk factors included atopic heredity, recurrent upper respiratory tract infections and breast-feeding less than 3 months, which appeared to interact multiplicatively with parental smoking. The environmental factors had a stronger influence in the youngest age group, and the overall attributable proportion associated with parental smoking, short breast-feeding period and exposure to pets in the household was 43%. It is clear that successful primary prevention could dramatically reduce the incidence of wheezing bronchitis in children.

No abstract

Risk factors for severe wheezing bronchitis were studied in children aged 4 months to 4 years in need of hospitalization. The children included in the study consisted of all cases generated from a geographically defined population, the catchment area of St Göran's hospital in Stockholm. The incidence was 3/1000 children and year, during the two years of observation, with the highest rate in boys under the age of 18 months (4.7/1000). Symptoms of a preceding upper respiratory tract infection were reported in 90% of the cases, but a viral etiology could only be demonstrated with virus isolation in 26%. Respiratory syncytial virus was the most common finding in younger children. Rhinovirus was primarily seen in older children with a history of previous wheezing. Regardless of whether the cases had a positive or negative virus isolation they showed the same seasonal distribution. Furthermore, there was no difference in risk factors between children with a positive and negative virus isolation. Children older than 18 months with negative virus isolation had higher IgE levels than those with positive isolation, suggesting that atopy is of greater importance in this group.