(P-354) A Retrospective Database Study to Evaluate Incidence of Influenza and Influenza-like Illness (ILI) Among Rheumatoid Arthritis (RA) Patients Taking Conventional Synthetic Disease Modifying Antirheumatic Drugs (csDMARD)

Background: Influenza is a seasonal acute respiratory illness caused by influenza A, B, or C viruses. Patients with immune-mediated diseases such as RA are known to have an increased risk of infections compared to the general population. There are limited data about incidence of influenza and ILI in RA patients treated with immunosuppressive drugs.

Objectives: To estimate the incidence of influenza and ILI and the frequency of influenza-related conditions in RA patients who initiated treatment with csDMARD.

Methods: This is a retrospective cohort study involving secondary analysis of Optum Electronic Health Record (EHR) database in the United States consisting of longitudinal health information from patients derived from participating healthcare provider organizations. Study period is 1 June 2014 through 31 May 2019.
All patients who have at least one inpatient or two outpatients (7-365 days apart) diagnosis codes (International Classification of Diseases, 9th and 10th revision) for RA, at least 6 months of continuous enrolment, age >=18, evidence of initiation for at least 1 approved csDMARD were followed from csDMARD start date until the date of event of interest, treatment discontinuation, death date, study end date or end of enrolment in the database. csDMARD Initiators are defined as those with a prescription for a drug they had not previously been prescribed during the 180 days baseline period. Exposure to csDMARD are defined using the National Drug Code (NDC) for dispensed or administrated medications and procedure codes for injection or infusion.
Baseline demographics are analyzed. Incidence rates for influenza and ILI and frequency of influenza-related hospitalization and mortality are reported.

Results: We found 114,507 RA patients who are initiators of csDMARD. For these patients, the mean age is 60.62 (SD 14.19) with 76.24% female; the incidence rates of influenza and ILI are 12.2 (95% CI 11.6 -12.8) and 175.7 (95% CI 173.1-178.2) per 1000 person-years, with 1,455 and 18,479 cases respectively. Among the influenza patients, 417 (28.7%) were hospitalized within 30 days post 1st influenza diagnosis, 7 (0.5%) had in-hospital death, and 63 (4.3%) died of any cause within 90 days post 1st influenza diagnosis.

Conclusions: The results provide evidence to inform prescribers about the development of influenza, ILI and associated complications in RA patients treated with csDMARD. Expansion of the study to other immunosuppressive drugs for future research is warranted.