Risk factors for reported influenza and influenza-like symptoms in patients with rheumatoid arthritis

To determine the prevalence and predictors of influenza and influenza-like symptoms in patients with rheumatoid arthritis (RA).

Questionnaires were sent to patients registered as having RA and they were asked to fill in per month any period and details of influenza-like symptoms and vaccination. An experienced rheumatologist assessed the level of disease activity and use of anti-rheumatic medication. The prevalence of reported influenza (fever > 38°C, headache, muscle soreness, and coughing and/or dyspnoea) and influenza-like symptoms was determined and risk factors were identified by logistic regression analysis.

Of the 1692 patients approached, 783 (46%) patients were eligible for follow-up. Fifty per cent of the patients reported influenza-like symptoms, 5.9% had symptoms suggesting influenza, and 74% reported vaccination. The prevalence of influenza and influenza-like symptoms per month ranged from 0.0% to 2.3% and from 10.4% to 19.7%, respectively. Anti-tumour necrosis factors (anti-TNFs) [odds ratio (OR) 2.4, 95% confidence interval (CI) 1.2-4.8] and body mass index (BMI) (OR 1.06, 95% CI 1.0-1.1) were independently associated with symptoms of influenza. A trend was found for patients not in remission, patients using leflunomide, and patients with previous lung conditions. Independent risk factors of influenza-like symptoms were age (OR 0.98, 95% CI 0.97-0.99), female gender (OR 1.8, 95% CI 1.3-2.5), influenza vaccination (OR 1.6, 95% CI 1.1-2.4), and previous lung condition (OR 1.7, 95% CI 1.2-2.4).

In 2009-2010, the prevalence of reported influenza in patients with RA was 5.9%. Patients using anti-TNFs and with higher BMI seemed to be more at risk for influenza symptoms. Milder upper respiratory tract infections were reported more often by females, younger patients, and those vaccinated against influenza or with previous lung conditions.