Prognostic factors of asthma severity: a 9-year international prospective cohort study.

Background: The natural history of asthma severity is poorly known.
Objective: To investigate prognostic factors of asthma severity.
Methods: All current patients with asthma identified in 1991 to 1993 in the European Community Respiratory Health Survey were followed up, and their severity was assessed in 2002 by using the Global Initiative for Asthma categorization (n = 856). Asthma severity (remittent, intermittent, mild, moderate, severe) was related to potential determinants evaluated at baseline and during the follow-up by a multinomial logistic model, using the intermittent group as the reference category for relative risk ratios (RRRs).
Results: Asthma severity measured at baseline was a determinant of a patient's severity at the end of the follow-up. At baseline, severe persistent had a poorer FEV1% predicted, a poorer symptom control, higher IgE levels (RRR, 2.06; 95% CI, 1.38-3.06), and a higher prevalence of chronic cough/mucus hypersecretion (RRR, 4.90; 95% CI, 2.18-11.02) than patients with intermittent asthma. Moderate persistent showed the same prognostic factors as severe persistent, even if the associations were weaker. Mild persistent had a distribution of prognostic factors that was similar to patients with intermittent asthma, although the former showed a poorer symptom control than the latter. Remission mainly occurred in patients with less severe asthma and was negatively associated with a change in body mass index (RRR, 0.86; 95% CI, 0.75-0.97). Allergic rhinitis, smoking, and respiratory infections in childhood were not associated with asthma severity.
Conclusion: Patients with moderate and severe persistent asthma are characterized by early deterioration of lung function. High IgE levels and persistent cough/mucus hypersecretion are strong markers of moderate/severe asthma, which seems to be a different phenotype from mild persistent or intermittent asthma.
Clinical Implications: Our results suggest that the evolution of asthma severity is to a large extent predictable.