Herpes zoster risk factors in a national cohort of veterans with rheumatoid arthritis.
BACKGROUND
Herpes zoster occurs more commonly in patients taking immunosuppressive medications, although the risk associated with different medications is poorly understood.


METHODS
We conducted a retrospective cohort study involving 20,357 patients who were followed in the Veterans Affairs healthcare system and treated for rheumatoid arthritis from October 1998 through June 2005. Cox proportional hazards regression was used to determine risk factors for herpes zoster and herpes zoster-free survival. Chart review was performed to validate the diagnosis of herpes zoster.


RESULTS
The incidence of herpes zoster was 9.96 episodes per 1000 patient-years. In time-to-event analysis, patients receiving medications used to treat mild rheumatoid arthritis were less likely to have an episode of herpes zoster than patients receiving medications used to treat moderate and severe rheumatoid arthritis (P < .001). Independent risk factors for herpes zoster included older age, prednisone use, medications used to treat moderate and severe rheumatoid arthritis, malignancy, chronic lung disease, renal failure, and liver disease. Among patients receiving tumor necrosis factor-alpha antagonists, etanercept (hazard ratio, 0.62) and adalimumab (hazard ratio, 0.53) were associated with a lower risk of herpes zoster. There was excellent agreement between the International Classification of Diseases, Version 9, Clinical Modification diagnosis of herpes zoster and diagnosis by chart review (kappa = 0.92).


CONCLUSIONS
Risk factors for herpes zoster included older age, prednisone use, medications used to treat moderate and severe rheumatoid arthritis, and several comorbid medical conditions. These results demonstrate that the Department of Veterans Affairs' national administrative databases can be used to study rare adverse drug events.
St. Louis Veterans Affairs Medical Center, St. Louis, Missouri 63106, USA. Jay.McDonald1@va.gov
Jay R
JR
McDonald
Angelique L
AL
Zeringue
Liron
L
Caplan
Prabha
P
Ranganathan
Hong
H
Xian
Thomas E
TE
Burroughs
Victoria J
VJ
Fraser
Fran
F
Cunningham
Seth A
SA
Eisen
D000367:Age Factors; D000368:Aged; D001172:Arthritis, Rheumatoid / Q000150:complications*; D015331:Cohort Studies; D005260:Female; D006562:Herpes Zoster / Q000453:epidemiology*; D006801:Humans; D007166:Immunosuppressive Agents / Q000009:adverse effects / Q000627:therapeutic use; D015994:Incidence; D008297:Male; D008875:Middle Aged; D012189:Retrospective Studies; D012307:Risk Factors; D014728:Veterans
D007166:Immunosuppressive Agents