Incidence rates of asthma, rhinitis and eczema symptoms and influential factors in young children in Sweden.

AIM

To estimate the incidence rates for asthma, rhinitis and eczema symptoms and to investigate the importance of different influential factors for the incidence of these symptoms.

METHODS

The Dampness in Building and Health study commenced in the year 2000 in Värmland, Sweden with a parental questionnaire based on an ISAAC protocol to all children in the age of 1-6 years. Five years later a follow-up questionnaire was sent to the children that were 1-3 years at baseline. In total, 4779 children (response rate = 73%) participated in both surveys and constitute the study population in this cohort study.

RESULTS

The 5-year incidence of doctor-diagnosed asthma was 4.9% (95% CI 4.3-5.3), rhinitis was 5.7% (5.0-6.4) and eczema was 13.4% (12.3-14.5). However, incidence rates strongly depend on the health status of the baseline population. Risk factors for incident asthma were male gender and short period of breast-feeding. Allergic symptoms in parents were also a strong risk factor for incident asthma, as well as for rhinitis and eczema.

CONCLUSION

When comparing incident rates of asthma between different studies it is important to realize that different definitions of the healthy baseline population will give rise to different incident rates.