Background/Purpose: Rheumatoid Arthritis (RA) is associated with increased incidence of seasonal influenza and its complications. Population-based studies on outcomes are lacking. The aim of our study was to evaluate the impact of RA on in-hospital mortality, length of stay, and hospitalization costs in patients with influenza.

Methods: We examined National Inpatient Sample data from 2000-2012. We performed a case-control study in which we included all discharges with influenza as primary diagnosis and RA (ICD 9 coded as 714.xx) as secondary diagnosis as cases (discharges with any comorbidities were excluded); while those with influenza as primary diagnosis and no comorbidities including RA as controls. The main outcomes included in-hospital mortality, length of stay, and hospitalization costs to study the impact of RA on influenza patients.

Results: A total of 1097 discharges had influenza as the primary diagnosis for admission. A total of 543 patients had influenza with RA (study group), and 554 had influenza without RA (control group). (Table 1) Both the groups who had any comorbidities listed as a secondary diagnosis were excluded to exclude the impact of other comorbidities on outcomes. There was no difference in mortality in patients with influenza with or without RA (0.5% vs 0.2%, P = .31). However, patients with influenza and RA had increased length of hospital stay (3.8 vs 2.1 days, P < .001), and higher hospitalization costs ($15,826 vs $5,953, P < .001). On multivariate analysis, RA was independently associated with increased hospital stay and higher hospitalization costs; but not mortality.

Conclusion: RA appears to be associated with increased length of stay and hospitalization costs in patients with influenza.

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ACR Meeting Abstracts - https://acrabstracts.org/abstract/impact-of-rheumatoid-arthritis-on-influenza-related-complications-a-population-based-cohort-study/