New estimate: More than one-third of US adults have arthritis

John Murphy, MDLinx | November 29, 2017

The prevalence of arthritis in adult Americans has been substantially underestimated, especially among those younger than 65 years, according to clinical epidemiologists in a recent study published in Arthritis & Rheumatology. Their new arthritis prevalence estimate is 68% higher than the previously reported national estimate, which hadn’t corrected for measurement errors in its surveillance methods.

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Arthritis underestimated, especially under age 65

Arthritis affects a much higher percentage of the US adult population and at a younger age than previously thought, researchers report.

Until now, national estimates of arthritis prevalence have relied on a single survey question asking subjects whether they were diagnosed with arthritis by a physician. But this method didn’t take into account patients who had reported joint symptoms on surveys but weren’t diagnosed with arthritis. That’s why sensitivity of this surveillance definition has been only 53% in subjects aged 45-64 years and 69% in subjects aged 65 years and older. 

To correct for this, epidemiologists S. Reza Jafarzadeh, DVM, MPVM, PhD, and David T. Felson, MD, MPH, both of Boston University School of Medicine, Boston, MA, developed a method for arthritis surveillance based not only on doctor-diagnosed arthritis, but also on chronic joint symptoms and symptoms lasting longer than 3 months.

“We aimed to estimate arthritis prevalence based on an expansive surveillance definition that is also adjusted for the measurement errors in the current definition,” Drs. Jafarzadeh and Felson wrote.

Using data from 33,672 participants in the 2015 National Health Interview Survey, the researchers found that arthritis affects a much higher percentage of the US adult population and at a younger age than previously thought. Among adults aged 18-64 years, 19.3% of men and 16.7% of women reported joint symptoms without having a doctor’s diagnosis of arthritis. For participants 65 years of age and older, 15.7% of men and 13.5% of women reported the same.

When the researchers applied their expanded definition of arthritis, they found that the prevalence in adults aged 18-64 years was 29.9% in men and 31.2% in women. In subjects aged 65 and older, the prevalence was 55.8% in men and 68.7% in women.

In total, arthritis affected 91.2 million adults (36.8% of US adults) in 2015, including 61.1 million of those aged 18-64 years (24.7% of US adults). This estimate is 68% higher than the previous estimate of 52.9 million American adults with diagnosed arthritis. This higher prevalence is due in large part to the previous underestimate of arthritis in adults under 65 years of age, the researchers noted.

“Our findings are important because of underestimated, yet enormous, economic and public health impacts of arthritis, including health-care costs and costs from loss of productivity and disability” among adults younger than age 65 years, Dr. Jafarzadeh said. “Studies have reported a rising rate of surgeries such as total knee replacement that outpaced obesity rates in recent years, especially among younger adults affected by arthritis.”

Current methods of estimating arthritis prevalence, which have been used since 2002, should be revised to increase accuracy, the researchers recommended.

This study was supported by a grant from the National Institutes of Health.

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