Fall and winter are more than just seasons for chilly weather and festive holidays. This time of year is cold and flu season, with infection rates rising in October and peaking in January, according to the Centers for Disease Control and Prevention. People with autoimmune diseases like rheumatoid arthritis are at higher risk for developing both bacterial and viral infections. Likewise, researchers are trying to find ways to predict which patients may be most susceptible.

This higher susceptibility in people with RA is due to both their malfunctioning immune system, which is focused more on attacking the body’s healthy joints than fighting off invading particles, and the immunosuppressant drugs that most people with RA take to control the disease process, says Eric Matteson, MD, chair of rheumatology at the Mayo Clinic in Rochester, Minn.

“When you have rheumatoid arthritis, which is a serious disease, you need to have treatment for it. Even if that treatment carries risks of infection, people still do better with treatment than without it. So we thought, what can we do to predict who is at higher risk?” says Dr. Matteson.

He and three colleagues explored all the factors that play into a person’s risk of acquiring cold, flu or pneumonia, or even urinary-tract infections which are less seasonal. They then developed a score so physicians can know which patients have the highest susceptibility. Their findings were published in the September 2012 issue of the medical journal Arthritis & Rheumatism.

“We looked at different variables, and looked at the characteristics of people with RA that seem to play a role in infection risk,” he says. These include:

  • Age
  • Corticosteroid use (greater than 10 milligrams of prednisone a day)
  • Disease activity as measured by tests like sedimentation rate, or RA that is not well controlled by drug treatments
  • Presence of RA complications such as vasculitis or lung disease
  • Presence of serous comorbidities like diabetes, alcoholism or emphysema

“So these are traditional things we think about when we look at infection risk, and things that are RA-specific,” says Dr. Matteson. “These coexisting conditions really identify if a person is at especially high risk of infection.”

The RA infection risk formula is complicated and cannot be calculated yet in an office or clinical setting, he adds. However, the data may help doctors determine which patients may be good candidates for clinical drug trials for RA, he says.