DPB has its highest prevalence among the Japanese, at 11 per 100,000 population.[4] Korean,[21] Chinese,[22] and Thai[23] individuals with the disease have been reported as well. A genetic predisposition among East Asians is suggested.[9] The disease is more common in males,[24] with the male to female ratio at 1.4–2:1 (or about 5 men to 3 women).[4] The average onset of the disease is around age 40, and two-thirds of those affected are non-smokers, although smoking is not believed to be a cause.[7] The presence of HLA-Bw54 increases the risk of diffuse panbronchiolitis 13.3-fold.[25]