Background/Purpose: Increased risk of infections has been recognized in patients with psoriatic arthritis (PsA) compared to those without PsA. Immunomodulatory effects of PsA, immunosuppressive therapies and associated comorbidities might all play a role. However, the rate of hospitalizations with serious infections in patients with PsA is largely unknown. We used the National Inpatient Sample (NIS) to compare hospitalizations for serious infections in patients with and without PsA in the US from 2000-2014.

Methods: Using NIS data from 2000-2014, we identified patients ≥18 years with PsA at any secondary diagnosis positions based on ICD-9 code 696.0. For each patient with PsA, a matched control of the same age (± 1 year), sex, race/ethnicity and NIS stratum (based on hospital’s census region or division, ownership/control, location/teaching, and bed size) was randomly selected. We evaluated 8 different infections as primary diagnoses: sepsis/bacteremia, pneumonia, urinary tract infection, skin and soft tissue infections, septic arthritis, osteomyelitis, brain/spinal cord infections and opportunistic infections. We compared the hospitalization rates for each infection among all hospitalizations with and without a secondary diagnosis of PsA. Hospitalized infection rates were estimated as the number of hospitalizations with primary discharge diagnosis of infection divided by the total number of hospitalization in the groups. Analyses were weighted to account for the sampling design of the NIS.

Results: NIS database from 2000-2014 contained 53,788 (weighted count, N=265,842) hospitalizations in the PsA and (weighted count, N=266,082) in the matched non-PsA cohort. Mean age at hospitalization for patients with PsA was 60 years (SD: 14.3) and 56% were female. Overall, there were an estimated 25,681 PsA and 15,014 non-PsA hospitalizations with a primary discharge diagnosis of infection, which corresponded to rates of 9.6 and 5.6 per 100 hospitalizations observed in the PsA and non-PsA cohorts, respectively (Rate ratio: 1.79, 95% CI: 1.71 – 1.88). While highest number of hospitalizations was observed for skin/soft tissue infections, sepsis/bacteremia and pneumonia in both groups, the highest differences in the rate ratio among the two groups were observed for septic arthritis, brain/spinal cord infections and opportunistic infections (Table).

Conclusion: Our study shows that patients with PsA have a higher proportion of hospitalizations for serious infections compared with non-PsA patients. Whether this difference is secondary to the immunosuppressive agents used in PsA or due to the immunologic disturbance associated with PsA itself would require careful evaluation in dedicated PsA studies. Future work will estimate rates of serious infections among all patients with PsA in the US and will also examine yearly trends in the rates of serious infections for patients with PsA.