Ankylosing spondylitis incidence similar among men, women in study of US Army veterans
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In contrast to some previous studies, an analysis of U.S. Army personnel found that the incidence of ankylosing spondylitis was similar between men and women, according to data published in Arthritis Care & Research.
“Despite the impact of AS, its incidence rates remain sub-optimally characterized,” Michael H. Weisman, MD, of the Stanford University School of Medicine, and colleagues wrote. “The only population-based published study addressing the incidence of AS in the U.S. examined clinically recognized cases of AS in Olmsted County, Minnesota, over a 30-year period from 1980-2009.”
“The overall reported age-adjusted incidence was 3.1/100,000 patient years, and males were three times as likely to have the disease compared to females,” they added. “The study population was relatively homogeneous, being 100% white in 1980-1989 and 80% white in 2000 to 2009. An additional review of health administrative data from Ontario, Canada, for 1995 to 2010 revealed increasing AS incidence rates among females and a consequent decrease in the male/female AS prevalence ratio from 1.7 to 1.21 over that time period. That study did not report the race distribution for its subjects.”
To examine any sex-based differences in the incidence of AS, Weisman and colleagues analyzed the Stanford Military Data Repository, a longitudinal electronic collection of
administrative and medical records on active-duty U.S. Army personnel. Focusing on the period from March 2014 to June 2017, the researchers included in their analysis a total of 728,556 individuals who underwent clinical practice guideline-directed screening for chronic back pain.
Demographic and military service data were obtained via official personnel records from the Defense Manpower Data Center. Clinical data were accessed through the Military Health System Data Repository, which archives information from the electronic health records of worldwide care provided to U.S. service members in military and civilian health care facilities. The primary outcome was incident AS.
According to the researchers, a total of 438 individuals — or 0.06% of the included population — were diagnosed with AS at least once during the study period. The total incidence of AS was 27.22 per 100,000 person-years. Male patients experienced a slightly, but not significantly, lower AS incidence, at 26.53 per 100,000 person-years, than female patients, at 31.36 (IRR = 1.16; 95% CI, 0.91-1.49).
The researchers noted that AS incidence among female patients aged 24 years and younger was nearly twice as high compared with that of male patients (IRR = 1.93; 95% CI, 1.13, 3.29). Although female patients experienced a lower incidence rate than male patients among those aged 45 to 54 years, the difference was not statistically significant (IRR = 0.77; 95% CI, 0.33-1.79).
In the multivariable logistic regression analysis, the adjusted odds for AS were slightly, but not significantly, lower among male patients compared with female patients (aOR = 0.79; 95% CI, 0.61-1.02). The odds for AS increased in a “relatively monotonic fashion” with age, resulting in a greater than seven-fold increase in those aged 45 years and older, compared with the youngest patients (aOR = 7.3; CI, 5.7-10.3). The researchers additionally found that white patients were at 39% higher adjusted odds for being diagnosed with AS, compared with Black patients (CI, 1.01-1.66).
“This study is the first of its kind to examine incidence of AS in the United States from a large working-age adult population racially and ethnically similar to the U.S. population,” Weisman told Healio Rheumatology. “We found that AS incidence among males and females is relatively comparable when we examined a population that experiences regular medical screening associated with free universal health care.”
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