Is the ebb of asthma due to the decline of allergic asthma? A prospective consultation-based study by the Swiss Sentinel Surveillance Network, 1999-2005

Objective. There are conflicting views on time trends of asthma and atopy during the last 10-15 years. Additional confusion is caused by the term of asthma which is a unifying name for different phenotypes. Asthma has been a topic for investigation to the Swiss Sentinel Surveillance Network (SSSN) since 1989. The objective of the actual study was to determine the influence of the allergic and non-allergic components of asthma on time trends from 1999 to 2005. Methods. Primary care physicians participating in the SSSN were guided by diagnostic criteria for asthma. Rates of asthma episodes per 1000 consultations were calculated for all, for first and subsequent asthma episodes and for allergic and non-allergic asthma. Allergic asthma was defined as asthmatic manifestations in conjunction with eczema and/or hay fever. The smoothed time trend and its 95% confidence intervals were determined using generalized additive models with a loess smoother adjusting for seasonality. Results. Consultations for allergic asthma have decreased between 1999 and 2005. Looking at different age groups, asthma associated with hay fever was reported with decreasing frequency in all age groups, whereas when associated with eczema, the other used marker of allergic asthma, slightly increased among young children. Conclusions. The decrease of consultations for asthma is most probably due to the allergic component of asthma. Diagnostic shift over time and ready available medications probably contributed to this phenomenon. Our findings indicate a real decline of allergic asthma. Practice recommendations. Consultations for asthma have decreased over recent years. The decrease of consultations for asthma is most probably due to the allergic component of asthma. Diagnostic shift over time and available medications probably contributed to this phenomenon. Strength of Recommendation Taxonomy (SORT) rating: strength of recommendation = C, level of evidence = 3.