Can Sex Predict the Incidence of Ankylosing Spondylitis in the US Population?

gender spectrum
gender spectrum
Using the Stanford Military Data Repository, researchers determined the incidence of ankylosing spondylitis between men and women.

Contrary to results of a previous study that reported a higher incidence of ankylosing spondylitis (AS) among men, findings from a recent study published in Arthritis Care & Research indicated that the incidence of AS among US military service members were similar between men and women.  

The incidence of AS is not well characterized. The only population-based study to date was conducted in Olmsted County, Minnesota, which indicated that men were 3 times more likely than women to have AS.  

The current study measured the incidence of AS in US Army personnel who underwent annual screenings for chronic back pain between March 2014 and June 2017. Researchers determined AS using the International Classification of Diseases, Ninth Revision (ICD-9) codes through September 2015 and ICD-10 codes for the remainder of the study.

A total of 728,556 individuals were screened for a period of 1,609,639 person-years. The incidence of AS was 27.22 per 100,000 person-years. Women had a slightly higher incidence of AS than men, but the difference was not statistically significant (incidence rate ratio [IRR], 1.16; 95% CI, 0.91-1.49; P =.233). However, the incidence of AS increased with age. Individuals aged 45 years and older were more than 7 times more likely to be diagnosed with AS than those aged younger than 24 years (adjusted odds ratio [aOR], 7.30; 95% CI, 5.17-10.32; P <.001). White US Army personnel had a higher incidence of AS than Black personnel (aOR, 1.39; 95% CI, 1.01-1.66; P =.038).

Limitations of the study included the inability to identify the onset of symptoms of AS and the nonrepresentative population of individuals in the US Army who are relatively younger and fitter.

The researchers concluded, “The incidence of AS in the US has been under-studied and incompletely characterized. Our findings challenge the widely held belief that AS in the US occurs substantially more frequently in [men] than [women]. That conclusion is based on widely accepted conventional wisdom from clinical experience and, in part, on the single incidence study conducted in Olmsted County, Minnesota. Our results derived from a population of adults in the US Army from 2014 to 2017 suggests that the incidence of AS in [men] and [women] is similar. We also found that that the rate of AS remains greater among White [individuals] [compared with] Black [individuals]. We encourage additional investigations utilizing other populations.


Nelson DA, Kaplan RM, Kurina LM, Weisman MH. Incidence of ankylosing spondylitis among male and female United States Army personnel. Arthritis Care Res. Published online August 30, 2021. doi:10.1002/acr.24774.