[Epidemiological study on the incidence of rheumatoid arthritis in adults in Yinzhou district, Ningbo city from 2011-2020].

Objective: To describe the distribution and trend of rheumatoid arthritis (RA) in adults in the Yinzhou district from 2011 to 2020 and compare the incidence differences in different ages and genders. Methods: Using the retrospective cohort design, we collected all new cases diagnosed with RA between 2011 to 2020 from the Yinzhou Regional Health Information Platform (YRHIP). Poisson distribution was used to estimate RA's incidence density and 95% CI . Results: From 2011 to 2020, 1 280 012 permanent residents in Yinzhou district were included, of which 665 361 were female (51.98%). The total follow-up person-years were 7 198 513.61, and the median follow-up person-year was 5.41 years ( P ₂₅ =3.50, P ₇₅ =8.32). During the study period, there were 2 350 new cases of RA, of which 1 460 were female (62.13%). The 10-year incidence density of the population was 32.65/100 000 person-years (95% CI : 31.34/100 000 person-years-33.99/100 000 person-years), that of females was 39.17/100 000 person-years (95% CI : 37.19/100 000 person-years-41.24/100 000 person-years), and that of the male was 25.64/100 000 person-years (95% CI : 23.98/100 000 person-years-27.38/100 000 person-years), the gender difference was statistically significant ( P <0.001). The incidence risk in all age groups above 30 years old was higher than that in the 18-29 years old group ( P <0.001), and the incidence risk increased with age from 18-79 years old while decreased slightly with age ≥80 years old. The lowest incidence density was 15.30/100 000 person-years in 2013 (95% CI :12.62/100 000 person-years-18.38/100 000 person- years), and the highest was 56.70/100 000 person-years in 2016 (95% CI : 51.24/100 000 person- years - 62.58/100 000 person-years), with statistically significant differences among different years ( P =0.004). Conclusions: From 2011 to 2020, the incidence density of RA in adults in Yinzhou district first increased, then decreased, and tended to stabilize. There were differences in incidence density in different years, ages, and genders.