Study design and research database
We designed a population-based retrospective cohort study. Here, the study data were extracted from the claims data in the Longitudinal Health Insurance Database 2000 (LHID2000); which includes systemically collected claims data of 1 million National Health Insurance (NHI) as well as the random samples in Taiwan NHI Research Database (NHIRD). NHIRD, managed by the National Health Research Institutes, contains data of beneficiaries of the NHI program established in 1995 to provide comprehensive and universal health care coverage to approximately 99% Taiwan residents. NHIRD include data on enrollment files, claims data, disease diagnose, prescriptions, outpatient visits, and hospital admissions. All diagnoses are coded using International Classification of Diseases, Ninth Revision, Clinical Modification (ICD-9-CM) diagnostic codes. To ensure data privacy, patient data are released to researchers in an electronically encrypted form and thus, the requirement to obtain informed consent was waived. This study has been approved by the Research Ethics Committee at China Medical University Hospital (CMUH104-REC2–115-CR-4).
Data availability statement
The dataset used in this study is held by the Taiwan Ministry of Health and Welfare (MOHW). The MOHW must approve our application to access this data. Any researcher interested in accessing this dataset can submit an application form to the Ministry of Health and Welfare requesting access. Please contact the staff of MOHW (Email: stcarolwu@mohw.gov.tw) for further assistance. Taiwan Ministry of Health and Welfare Address: No.488, Sec. 6, Zhongxiao E. Rd., Nangang Dist., Taipei City 115, Taiwan (R.O.C.). Phone: + 886–2–8590-6848. All relevant data are within the paper.
Study population
We identified patients first diagnosed as having sciatica (ICD-9-CM 724.3) between January 1, 2000 and December 31, 2012, and included them in the sciatica cohort. The index date was defined as the date of sciatica diagnosis. We excluded patients aged < 20 years, and with a HZ history before the index date. Every patient with sciatica was randomly age (every 5-year interval), sex and index date matched with a control individual without sciatica from the same database and then this individual was assigned to the control cohort under the same criteria.
Outcome and covariate assessment
The outcome of interest was a new diagnosis of HZ (ICD-9-CM 053) between January 1, 2000 and December 31, 2013. All individuals were followed until HZ occurrence, withdrawal from NHI, death, or December 31, 2013, whichever occurred first. We considered several covariates as potential confounders including sex, age, and baseline comorbidities. Inpatient and outpatient data were used to define the status of comorbidities including chronic kidney disease (ICD-9-CM 585and 586), obesity (ICD-9-CM 278), diabetes (ICD-9-CM 250), coronary artery disease (ICD-9-CM 410–414), depression (ICD-9-CM 296.2, 296.3, 300.4 and 311), and lumbar disc herniation (ICD-9-CM 722.10).
Statistical analysis
Characteristics of all included individuals were first analyzed descriptively. The differences of categorical and continuous variables between the sciatica and control cohorts were tested using the t and chi-square tests. The incidence rate was defined as the number of events per 1000 person-years. Cox proportional hazards regression model adjusted for age, sex and comorbidity was used to determine the association between sciatica and HZ risk. The results were presented as a hazard ratio (HR) with accompanying 95% confidence interval (CI). We estimated the cumulative incidence of HZ in the sciatica and control cohorts by using the Kaplan–Meier method, and the differences were examined using the log-rank test. HZ risk in the two cohorts was further analyzed after age, sex and comorbidity stratification. A two-sided p of < 0.05 was considered statistically significant. All data processing and statistical analyses were performed using SAS (version 9.4; SAS Institute Inc., Cary, NC, USA).