Background/Purpose:

Long term data on infection risk in ankylosing spondylitis (AS) are sparse and derived mainly from RCTs.  Anti-TNF therapy is increasingly used in AS, with infection being the most important adverse event.  In rheumatoid arthritis (RA), serious infections are common adverse events of anti-TNF therapy with an incidence of 4-10 per 100 patient-years (pys).  We aimed to investigate the frequency of infections in AS and to identify factors predisposing to infection.

Methods:

Data were extracted from a longitudinal observational database for patients meeting Assessment of SpondyloArthritis international Society (ASAS) criteria for axial SpA.  Infection rates were calculated and multivariate analysis using a GEE model was performed to investigate the association of independent variables with infection.

Results:

440 patients (73% male) were included in the analysis.  259 infections (23 serious, defined as requiring IV antibiotics or hospitalization) occurred during 1712 pys of follow-up.  80% were bacterial and 15% were viral.  The most common site of infection was lung, followed by skin, genitourinary tract, upper respiratory tract, sinus and gastrointestinal tract.  Ninety percent of infections were treated with antibiotics, of which 10% required intravenous antibiotics. 

The overall rate [95% CI] of any infection was 15 [13, 17] / 100 pys and the serious infection rate was 1.3 [0.9, 2.0]/ 100 pys.  Of the 264 patients prescribed a biologic drug during a total follow up time of 684 pys on biologic therapy, 127 infections (10 serious) were recorded in 101 patients.   The rate of any infection while on a biologic drug was 19 [16, 22] / 100 pys and the serious infection rate was 1.5 [0.7, 3.0] / 100 pys.  Of the 186 patients never prescribed a biologic drug during a total follow up time of 651 pys, 91 infections (12 serious) were recorded in 71 patients.  The rate of any infection was 14 [11, 17] / 100 pys and the serious infection rate was 1.8 [1.0, 3.0] /100 pys.  There was no significant difference in the rates for patients on biologic drugs compared to patients never on biologic drugs for any infection (p=0.78) or serious infection (p=0.19). 

In the univariate analysis, DMARD use and glucocorticoid use were associated with an increased risk of infection.  In the multivariate analysis, only DMARD use remained significant (OR 1.76 [1.12, 2.76], p<0.01).  However, the number of patients on DMARDs was small (n=31). Biologic use, age, disease duration, smoking status, BASFI, BASDAI, comorbidity score and hospitalizations were not associated with an increased risk of infection. 

Conclusion:

Biologic therapy in this longitudinal AS cohort was not associated with an increased risk of infection, while DMARD use appeared to confer risk of infection.  However, most infections were not serious and the serious infection rate was much lower than previously reported in RA.  Our findings represent a “real-world” experience which includes AS patients with comorbidities which often exclude them from RCTs.  The apparent lower rate of infection in patients with AS compared to RA may reflect several factors: the younger age and lower frequency of comorbidities in AS, differing immunogenetic mechanisms in the respective diseases, and differences in treatment.

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ACR Meeting Abstracts - https://acrabstracts.org/abstract/infection-risk-in-ankylosing-spondylitis-results-from-a-longitudinal-observational-cohort/