National trends in the prevalence of rheumatoid arthritis and osteoarthritis in South Korea, 1998–2021

Patient selection and data collection

This study used data from the Korea National Health and Nutrition Examination Survey (KNHANES), conducted between 1998 and 2021 by the Korea Centers for Disease Control and Prevention Agency (KDCA).^10,11. The study population included adults aged ≥ 19 years and data collected included information on age, gender, place of residence, body mass index (BMI), education level, income, alcohol consumption, smoking status and history of RA and OA.¹². We focused our research on the adult population, which is over 19 years old in South Korea. A nationally representative sample of 163,221 participants was used to examine the prevalence of RA and OA before and during the COVID-19 pandemic. The survey was conducted over 24 years and the number of participants surveyed in each year group was as follows: 51,515 in 1998-2001; 26,996 in 2005-2007; 20,070 in 2008–2010; 17,601 in 2011–2013; 17,129 in 2014–2016; 18,469 in 2017–2019; 5839 in 2020; and 5,602 in 2021.

The study protocol was approved by the Institutional Review Board of Kyung Hee University (KHUH 2022-06-042) and KDCA, and all participants provided written informed consent. Furthermore, the KNHANES provides accessible public access to its data, which can be used as a valuable resource for various epidemiological studies. This study followed the ethical guidelines established by relevant national and institutional review boards for human research and adhered to the 1975 Declaration of Helsinki, as amended in 2008.

Determination of RA and OA

The aim of our study was to investigate the risk factors associated with the two most common forms of arthritis, RA and OA, over a 24-year period, from 1998 to 2021. To achieve our research objective, we collected a large number surveyed participants and asked them the question, “Have you ever been diagnosed with RA or OA by a doctor?” Based on their answers, we divided the participants into three groups: RA, OA, and both¹³. We collected data on several potential risk factors associated with the development of RA and OA, such as age, gender, lifestyle habits and socio-economic status. We conducted statistical analyzes to examine the associations between these risk factors and the development of RA and OA and to identify patterns or trends that have emerged over 24 years.

Covariates

Covariates included age (19–29, 30–39, 40–49, 50–59, 60–69, 70–79, and ≥ 80 years), gender, region of residence (urban and rural)^14,15,16, BMI group, household income (lowest, second, third, and highest quartiles), education level (primary school or less, middle school, high school, and college or higher education), alcohol consumption (1–5 days/month, ≥ 6 days/month, and non-drinker) and smoking status (non-smoker, ex-smoker and smoker). BMI was subdivided into underweight (< 18.5 kg/m2).²), normal weight (18.5–22.9 kg/m²), overweight (23–25 kg/m2²), and obese (≥ 25.0 kg/m²) according to Asia-Pacific guidelines^17,18.

static analysis

The results of this study were presented using qualitative data, expressed in proportions or percentages. Weighted multivariate regression model analyzes were conducted to compare the estimates of each related factor before and during the COVID-19 pandemic, using weighted odds ratios (ORs) with 95% confidence intervals (CIs).¹⁹. The prevalence of RA and OA was calculated using data from the KNHANES, spanning the period 1998 to 2021, stratified by year group. A weighted complex sampling analysis was performed to ensure accurate estimation. Binomial or linear logistic regression models were used to calculate the ORs with 95% CIs or β coefficients with 95% CIs. To ensure the robustness of the main findings, a stratification analysis was performed in all regression models using variables such as gender, education level, region of residence and income. Furthermore, the ratio of ORs was calculated to estimate the interaction duration of each risk factor and identify groups that were more vulnerable to the patient with RA and OA during the pandemic. Overall, this study aimed to provide a comprehensive analysis of the impact of the COVID-19 pandemic on the prevalence of RA and OA and to identify the factors contributing to vulnerability to these conditions. The SAS software (version 9.4; SAS Institute, Cary, NC, USA) was used for statistical analyses, with a two-sided test, and a p-value ≤ 0.05 was considered statistically significant¹⁹.