West Sweden Asthma Study: prevalence trends over the last 18 years argues no recent increase in asthma.

Asthma prevalence has increased over the last fifty years, but the more recent changes have not been conclusively determined. Studies in children indicate that a plateau in the prevalence of asthma may have been reached, but this has not yet been confirmed in adults. Epidemiological studies have suggested that the prevalence of asthma in adults is approximately 7-10% in different parts of the western world. We have now performed a large-scale epidemiological evaluation of the prevalence of asthma and respiratory symptoms in adults between the ages of 16-75 in West Sweden. Thirty thousand randomly chosen individuals were sent a detailed questionnaire focusing on asthma and respiratory symptoms, as well possible risk factors. Sixty-two percent of the contacted individuals responded to the questionnaire. Asthma prevalence, defined as asthma diagnosed by a physician, was 8.3%. Moreover, the prevalence of respiratory symptoms was lower compared to previous studies. The most common respiratory symptom was any wheeze (16.6%) followed by sputum production (13.3%). In comparison with studies performed 18 years ago, the prevalence of asthma has not increased, and the prevalence of most respiratory symptoms has decreased. Therefore, our data argues that the continued increase in asthma prevalence that has been observed over the last half century is over.