Background: Adult onset asthma is poorly studied and there are few long-term clinical follow-up studies.

Aim: To study clinical characteristics of adult onset asthma in a 15-year follow-up.

Method: Within the Obstructive Lung Disease in Northern Sweden (OLIN) studies, a cohort of n=309 subjects with adult onset asthma (aged 20-60 years) was recruited during 1995-99. The cohort was followed up in 2012-14 (n=205). Structured interviews and clinical examinations including spirometry were performed at both recruitment and follow-up. Skin prick tests were performed at recruitment and blood samples for cell counts and IgE at the follow-up. Asthma control was classified according to GINA 2006.

Results: At follow-up n=182 (89%) still had asthma, while n=23 (11%) were in remission. Among individuals with persistent asthma, mean pre-bronchodilator FEV1 percent of predicted was 89.0 at follow-up, similar as recruitment 88.3. At recruitment 16.5% were smokers, and of these, 86.7% had quit smoking at follow-up. At follow-up, 39% had blood neutrophils ≥4.0x109/L, 23% had blood eosinophils ≥0.3x109/L, and 28% had specific IgE>0.35 IU/ml to any airborne allergen. Any respiratory symptoms were reported by 90% and 31% used medium or high dose inhaled corticosteroids (ICS), 20% low dose ICS whereas 20% had no treatment. 55% had controlled asthma, 32% partly controlled and 13% uncontrolled asthma.

Conclusion: In this 15-year follow-up of adult onset asthma, the majority had persistent asthma. Smoking and high proportion using ICS may contribute to the stable lung function. Still, it should be noted that merely around every other had well controlled asthma.