The problem with estimating how many people in the U.S. suffer from AS is that it can take many years to diagnose the disease. The first few years it can simply manifest itself with some level of back pain, which most people experience now and then. Therefore AS will not usually be considered an option.
Numbers on ankylosing spondylitis
AS differs from regular arthritis, which is known to become more prevalent with age. AS does not recognize age and people between 15-45 are especially affected. The age- and sex-adjusted incidence of AS is 0.4-14 per 100,000 person-years.
Prevalence of AS in the population increases to approximately 5% among patients who are HLA-B27 positive. < 15 : 30 persons
15-24 : 630
25-34 : 1,280
35-44 : 990
45-54 : 590
55-64 : 160
> Age of disease onset usually peaks in the second and third decades of life.
Approximately 80% of patients with ankylosing spondylitis experience symptoms at ≤30 years of age, while only 5% will have symptoms at ≥45 years of age.
< 15 : Men 0.7 % / Women 0.0%
15-24 : Men 14.9 % / Women 3.6 %
25-34 : Men 23.7 % / Women 6.4 %
35-44 : Men 18.2 % / Women 4.0 %
45-54 : Men 12.3 % / Women 3.3 %
55-64 : Men 2.5 % / Women 2.0 %
> 64 : Men develop ankylosing spondylitis three times as often as women, and it usually begins between the ages of 15 and 30, with people over 40 rarely developing the disease
Source: John Hopkins Arthritis Center