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Abstract

Objectives. The objectives of this study were to examine changes in the incidence and prevalence of RA between 1990 and 2014 and to explore if there is any geographic variation in the incidence and prevalence of RA in the UK.

Methods. This was a primary care–based prospective cohort study. People contributing acceptable data to Clinical Practice Research Datalink between 1 January 1990 and 31 December 2014 were included. Read codes were used to identify RA cases ⩾18 years of age. The prevalence and incidence rates for each year were standardized to the 2014 population and the regional incidence and prevalence of RA for the year 2014 were standardized to the overall population.

Results. The incidence and prevalence of RA was 3.81/10 000 person-years and 0.67%, respectively, in 2014. The annual incidence of RA decreased by 1.6% (95% CI 0.8, 2.5) between 1990 and 2014, with significant joinpoints at 1994 and 2002. The prevalence of RA increased by 3.7%/year (95% CI 3.2, 4.1) from 1990 to 2005 and decreased by 1.1%/year (95% CI 2.0, 0.2) between 2005 and 2014. There were significant differences in the occurrence of RA throughout different regions of the UK, with the highest incidence in East Midlands, Yorkshire and Humber and the highest prevalence in North East, Yorkshire and Humber.

Conclusion. The incidence of RA is decreasing, with a reduction in prevalence in recent years. There is significant geographic variation in the occurrence of RA in the UK. Further research is required to identify the reasons underlying this phenomenon so that public health interventions can be designed to further reduce the incidence of RA.

rheumatoid arthritis, incidence, prevalence, geographic variation

Rheumatology key messages

  • The incidence of RA in the UK is decreasing gradually.

  • The prevalence of RA in the UK has decreased recently.

  • There is significant geographic variation in the occurrence of RA in the UK.

Introduction

RA is the most common autoimmune inflammatory arthritis, with a prevalence of 0.5–1.0% and an incidence of 24–45/100 000 person-years [1, 2]. It occurs due to a combination of genetic, environmental and constitutional risk factors, but unlike gout and OA, paleo-epidemiologic studies do not provide convincing evidence that it has been around for longer than a few hundred years [3]. Moreover, unlike most common complex disorders such as type 2 diabetes [4], obesity [5] and hypertension [6] whose incidence and prevalence have increased over time, there is considerable controversy as to whether the incidence of RA has decreased rather than increased. While most studies report a progressive reduction in the incidence of RA in the USA, Finland and Japan [7–12], others have reported either an increasing incidence (USA and Denmark) [13–15] or stable incidence (Greece) [16] (Greece). Several explanations for the reduced incidence of RA, including birth cohort effect [17–19] and increased uptake of hormonal contraception [10–12, 20], have been suggested. However, the oral contraceptive hypothesis is not supported by all studies [12, 21] and the increase in the mean age of incident RA cases observed in cross-sectional studies conducted in the same geographic area several decades apart and used to suggest the presence of a birth cohort effect could be explained by an ageing general population [17, 18]. Moreover, it is difficult to draw definite conclusions on temporal trends in the incidence and prevalence of RA as many published studies are relatively small [8, 9, 12, 13, 15–17, 19, 21]. Thus it is necessary to revisit the temporal trends in the epidemiology of RA.

The overall aim of this study was to explore variations in the incidence and prevalence of RA in the UK between 1990 and 2014. The specific objectives were to (i) provide contemporary data on the epidemiology of RA, (ii) examine changes in the prevalence and incidence of RA between 1990 and 2014 and (iii) explore whether there is geographic variation in the occurrence of RA in the UK, as this may help explore possible environmental risk factors for the disease.

Methods

Source of data

Data from the Clinical Practice Research Datalink (CPRD) were used. The CPRD is one of the largest databases of longitudinal medical records from primary care. Established in 1987, it contains anonymized health care records from >13 million individuals and represents 8% of the UK population at any one time. The data in the CPRD undergoes thorough quality checks and is of reliable research quality with a high validity of recorded diagnoses, including a median proportion of cases with a confirmed diagnosis of 89% for 183 different conditions, including chronic autoimmune conditions [22]. The study was approved by the Independent Scientific Advisory Committee of the Medicines and Healthcare Regulatory Authority, London, UK (Ref: 15_101R).

Study population

The study comprised all participants who contributed acceptable quality data to the CPRD between 1 January 1990 and 31 December 2014. The denominator for prevalence estimation for each calendar year included all individuals registered on 1 July of each calendar year with a general practitioner (GP). For the incidence of RA, at-risk cohorts for each calendar year were constructed, which comprised all individuals registered with up-to-standard practices (practices meeting the specified data entry criteria) during the year specified who had never been coded as having RA before the latest of current registration date plus 365 days or 1 January of the calendar year specified. Person-years of follow-up were calculated from the latest of 1 January or the date of current registration plus 365 days to the earliest date of transfer out, incident RA diagnosis, death or 31 December of the specified year.

Definition of RA

RA was defined using a previously published medical Read code list [23]. This list was modified after discussions among the investigators [rheumatologists (A.A., M.D., C.-F.K.), academic GP with expertise in CPRD research (C.D.M.), statistician (M.J.G.) and epidemiologist (W.Z.)] to exclude medical Read codes for adult Still’s disease (N005.00), adult-onset Still’s disease (N04y200) and juvenile AS (N045000) since they are distinct diseases. The code list used by us may be obtained from the Rheumatoid Arthritis Codes table in supplementary Appendix S2, available at Rheumatology Online.

Case definition

Prevalent cases of RA were participants ⩾18 years of age on 1 July of each calendar year who had a medical Read code that had been used previously to identify cases with RA [23]. Information about RF, anti-CCP antibodies and DMARD prescriptions were not used for identifying RA cases, as serological testing and DMARD prescription rates vary over time and affect temporal trends in the epidemiology of RA. Incident cases of RA were those who had no medical code for RA prior to the latest of current registration date plus 365 days or 1 January of each calendar year but developed RA during that year and were ⩾18 years of age at the index date. To be eligible as an incident case, participants had to have at least 1 year registration prior to the first date of RA diagnosis, as this has been shown to reduce the risk of prevalent cases being counted as incident cases in chronic conditions such as RA [24]. To examine whether this period was sufficiently long to exclude these potentially prevalent cases, we also classified cases to have at least 3 years registration prior to the first date of RA diagnosis in a sensitivity analysis.

Statistical analysis

The point prevalence of RA on 1 July of each year was calculated and 95% CI calculated. Incidence rates by year were calculated using the number of incident RA cases during that year as the numerator and the total person-years occurring during the same year as the denominator. Incidence and prevalence rates were stratified by sex. Poisson regression was used to examine the association between sex and prevalent and incident RA.

To determine trends in the prevalence and incidence of RA, age-, sex- and length of data contribution–standardized prevalence and incidence of RA were calculated for each calendar year from 1990 to 2013 with the population structure in year 2014 as a reference. Ten year age bands were selected for age stratification. The incidence and prevalence were standardized for the length of data contribution, as the longer the period a person contributes data to the CPRD the greater the chance that a chronic health event will be recorded at some point. The length of data contribution of each patient was defined as the period from the current date of registration to 1 July of each calendar year for prevalence or to 1 January of the calendar year specified for incidence. The length of data contribution was categorized as 0–3, 4–6, 7–9 and ⩾10 years. Temporal trends in the incidence and prevalence of RA were examined using joinpoints analysis. For this the Joinpoint Regression Program was used [25] (see Joinpoint Analysis section of the supplementary data, available at Rheumatology Online).

The incidence rate of RA for each 10 year age band was calculated in 1994, 2004 and 2014 to look for the presence of a birth cohort effect. This was stratified by sex. Finally, the prevalence and incidence of RA were calculated separately for 13 regions in the UK for the year 2014 (see supplementary data section Regions of the UK, available at Rheumatology Online). To remove the effect of different age and gender structures, the prevalence and incidence were standardized to the overall CPRD population structure in 2014. Incidence rates were calculated and a likelihood ratio test was performed to find out if there was a statistically significant overall geographic variation in the incidence and prevalence. Choropleth maps were used to illustrate geographic variations. Data management and analysis were performed using Stata software version 13 (StataCorp, College Station, TX, USA). The significance level was P < 0.05.

Results

Prevalence and incidence

Of the 3 966 443 eligible individuals in 2014, 26 385 prevalent cases of RA were identified, giving a prevalence of 0.67% (95% CI 0.66, 0.67). Women had a higher prevalence [0.93% (95% CI 0.91, 0.94)] than men [0.40% (95% CI 0.39, 0.41)] with an age-adjusted rate ratio of 2.08 (95% CI 2.02, 2.13). The prevalence of RA increased with age (Fig. 1A).
Increasing prevalence and incidence of RA with age
Fig. 1

Increasing prevalence and incidence of RA with age

(A) Increasing prevalence of RA with age. (B) Increasing incidence of RA with age.

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There were a total of 3 413 043 person-years of follow-up in 2014 during which 1299 incident cases of RA were identified, giving an incidence of 3.81 (95% CI 3.61, 4.02) per 10 000 person-years. The incidence of RA increased with age (Fig. 1B). Women had a higher incidence per 10 000 person-years than men [5.09 (95% CI 4.75, 5.42) vs 2.51 (95% CI 2.28, 2.75)], with an age-adjusted incidence rate ratio of 1.85 (95% CI 1.65, 2.07).

Prevalence and incidence of RA between 1990 and 2014

In general, crude, age–sex standardized and age, sex and length of data standardized estimates of prevalence of RA increased over time (Table 1 and Fig. 2). The overall annual increase in prevalence was 2.10% (95% CI 1.5, 2.70). However, there was one significant joinpoint at 2005 (supplementary Fig. S1, available at Rheumatology Online). The prevalence of RA increased by 3.7% (95% CI 3.2–4.1) per year from 1990 to 2005 and decreased by 1.1% (95% CI 2.0, 0.2) per year from 2005 to 2014.
Table 1
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Prevalence of RA from 1990 to 2014

YearPopulationPrevalence, % (95% CI)
CrudeAge–sex standardizedAge–sex and duration of data contribution standardized
19903 118 3820.34 (0.34, 0.35)0.36 (0.36, 0.37)0.41 (0.38, 0.43)
19913 360 1310.38 (0.37, 0.38)0.40 (0.39, 0.41)0.43 (0.42, 0.44)
19923 566 9060.40 (0.40, 0.41)0.43 (0.42, 0.43)0.43 (0.42, 0.44)
19933 788 9480.43 (0.42, 0.43)0.45 (0.44, 0.46)0.48 (0.47, 0.49)
19944 021 7740.45 (0.44, 0.45)0.47 (0.46, 0.48)0.50 (0.49, 0.51)
19954 230 6290.46 (0.46, 0.47)0.49 (0.48, 0.49)0.52 (0.51, 0.54)
19964 431 7880.48 (0.47, 0.49)0.50 (0.50, 0.51)0.51 (0.51, 0.52)
19974 591 4760.50 (0.49, 0.50)0.52 (0.51, 0.52)0.55 (0.54, 0.56)
19984 693 2330.51 (0.51, 0.52)0.53 (0.53, 0.54)0.54 (0.53, 0.55)
19994 781 8980.53 (0.52, 0.53)0.55 (0.54, 0.55)0.55 (0.55, 0.56)
20004 860 6540.54 (0.54, 0.55)0.56 (0.56, 0.57)0.59 (0.58, 0.61)
20014 918 4670.56 (0.56, 0.57)0.58 (0.58, 0.59)0.62 (0.60, 0.63)
20024 952 1880.59 (0.58, 0.59)0.61 (0.60, 0.62)0.61 (0.61, 0.62)
20034 996 0920.61 (0.60, 0.61)0.63 (0.62, 0.63)0.67 (0.65, 0.68)
20045 039 3570.62 (0.62, 0.63)0.64 (0.64, 0.65)0.69 (0.68, 0.71)
20055 097 7460.64 (0.63, 0.65)0.66 (0.65, 0.67)0.76 (0.73, 0.78)
20065 096 9330.65 (0.64, 0.66)0.67 (0.66, 0.67)0.75 (0.72, 0.77)
20075 092 4820.65 (0.65, 0.66)0.67 (0.66, 0.68)0.67 (0.66, 0.68)
20085 068 3130.66 (0.65, 0.66)0.67 (0.66, 0.68)0.67 (0.67, 0.68)
20095 035 8950.66 (0.65, 0.67)0.67 (0.67, 0.68)0.67 (0.67, 0.68)
20104 946 0600.67 (0.66, 0.67)0.67 (0.67, 0.68)0.68 (0.67, 0.68)
20114 821 3770.67 (0.66, 0.67)0.67 (0.67, 0.68)0.67 (0.67, 0.68)
20124 724 8860.66 (0.66, 0.67)0.67 (0.66, 0.68)0.67 (0.67, 0.68)
20134 456 8950.66 (0.65, 0.67)0.67 (0.66, 0.67)0.67 (0.66, 0.67)
20143 966 4430.67 (0.66, 0.67)——
YearPopulationPrevalence, % (95% CI)
CrudeAge–sex standardizedAge–sex and duration of data contribution standardized
19903 118 3820.34 (0.34, 0.35)0.36 (0.36, 0.37)0.41 (0.38, 0.43)
19913 360 1310.38 (0.37, 0.38)0.40 (0.39, 0.41)0.43 (0.42, 0.44)
19923 566 9060.40 (0.40, 0.41)0.43 (0.42, 0.43)0.43 (0.42, 0.44)
19933 788 9480.43 (0.42, 0.43)0.45 (0.44, 0.46)0.48 (0.47, 0.49)
19944 021 7740.45 (0.44, 0.45)0.47 (0.46, 0.48)0.50 (0.49, 0.51)
19954 230 6290.46 (0.46, 0.47)0.49 (0.48, 0.49)0.52 (0.51, 0.54)
19964 431 7880.48 (0.47, 0.49)0.50 (0.50, 0.51)0.51 (0.51, 0.52)
19974 591 4760.50 (0.49, 0.50)0.52 (0.51, 0.52)0.55 (0.54, 0.56)
19984 693 2330.51 (0.51, 0.52)0.53 (0.53, 0.54)0.54 (0.53, 0.55)
19994 781 8980.53 (0.52, 0.53)0.55 (0.54, 0.55)0.55 (0.55, 0.56)
20004 860 6540.54 (0.54, 0.55)0.56 (0.56, 0.57)0.59 (0.58, 0.61)
20014 918 4670.56 (0.56, 0.57)0.58 (0.58, 0.59)0.62 (0.60, 0.63)
20024 952 1880.59 (0.58, 0.59)0.61 (0.60, 0.62)0.61 (0.61, 0.62)
20034 996 0920.61 (0.60, 0.61)0.63 (0.62, 0.63)0.67 (0.65, 0.68)
20045 039 3570.62 (0.62, 0.63)0.64 (0.64, 0.65)0.69 (0.68, 0.71)
20055 097 7460.64 (0.63, 0.65)0.66 (0.65, 0.67)0.76 (0.73, 0.78)
20065 096 9330.65 (0.64, 0.66)0.67 (0.66, 0.67)0.75 (0.72, 0.77)
20075 092 4820.65 (0.65, 0.66)0.67 (0.66, 0.68)0.67 (0.66, 0.68)
20085 068 3130.66 (0.65, 0.66)0.67 (0.66, 0.68)0.67 (0.67, 0.68)
20095 035 8950.66 (0.65, 0.67)0.67 (0.67, 0.68)0.67 (0.67, 0.68)
20104 946 0600.67 (0.66, 0.67)0.67 (0.67, 0.68)0.68 (0.67, 0.68)
20114 821 3770.67 (0.66, 0.67)0.67 (0.67, 0.68)0.67 (0.67, 0.68)
20124 724 8860.66 (0.66, 0.67)0.67 (0.66, 0.68)0.67 (0.67, 0.68)
20134 456 8950.66 (0.65, 0.67)0.67 (0.66, 0.67)0.67 (0.66, 0.67)
20143 966 4430.67 (0.66, 0.67)——
Table 1
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Prevalence of RA from 1990 to 2014

YearPopulationPrevalence, % (95% CI)
CrudeAge–sex standardizedAge–sex and duration of data contribution standardized
19903 118 3820.34 (0.34, 0.35)0.36 (0.36, 0.37)0.41 (0.38, 0.43)
19913 360 1310.38 (0.37, 0.38)0.40 (0.39, 0.41)0.43 (0.42, 0.44)
19923 566 9060.40 (0.40, 0.41)0.43 (0.42, 0.43)0.43 (0.42, 0.44)
19933 788 9480.43 (0.42, 0.43)0.45 (0.44, 0.46)0.48 (0.47, 0.49)
19944 021 7740.45 (0.44, 0.45)0.47 (0.46, 0.48)0.50 (0.49, 0.51)
19954 230 6290.46 (0.46, 0.47)0.49 (0.48, 0.49)0.52 (0.51, 0.54)
19964 431 7880.48 (0.47, 0.49)0.50 (0.50, 0.51)0.51 (0.51, 0.52)
19974 591 4760.50 (0.49, 0.50)0.52 (0.51, 0.52)0.55 (0.54, 0.56)
19984 693 2330.51 (0.51, 0.52)0.53 (0.53, 0.54)0.54 (0.53, 0.55)
19994 781 8980.53 (0.52, 0.53)0.55 (0.54, 0.55)0.55 (0.55, 0.56)
20004 860 6540.54 (0.54, 0.55)0.56 (0.56, 0.57)0.59 (0.58, 0.61)
20014 918 4670.56 (0.56, 0.57)0.58 (0.58, 0.59)0.62 (0.60, 0.63)
20024 952 1880.59 (0.58, 0.59)0.61 (0.60, 0.62)0.61 (0.61, 0.62)
20034 996 0920.61 (0.60, 0.61)0.63 (0.62, 0.63)0.67 (0.65, 0.68)
20045 039 3570.62 (0.62, 0.63)0.64 (0.64, 0.65)0.69 (0.68, 0.71)
20055 097 7460.64 (0.63, 0.65)0.66 (0.65, 0.67)0.76 (0.73, 0.78)
20065 096 9330.65 (0.64, 0.66)0.67 (0.66, 0.67)0.75 (0.72, 0.77)
20075 092 4820.65 (0.65, 0.66)0.67 (0.66, 0.68)0.67 (0.66, 0.68)
20085 068 3130.66 (0.65, 0.66)0.67 (0.66, 0.68)0.67 (0.67, 0.68)
20095 035 8950.66 (0.65, 0.67)0.67 (0.67, 0.68)0.67 (0.67, 0.68)
20104 946 0600.67 (0.66, 0.67)0.67 (0.67, 0.68)0.68 (0.67, 0.68)
20114 821 3770.67 (0.66, 0.67)0.67 (0.67, 0.68)0.67 (0.67, 0.68)
20124 724 8860.66 (0.66, 0.67)0.67 (0.66, 0.68)0.67 (0.67, 0.68)
20134 456 8950.66 (0.65, 0.67)0.67 (0.66, 0.67)0.67 (0.66, 0.67)
20143 966 4430.67 (0.66, 0.67)——
YearPopulationPrevalence, % (95% CI)
CrudeAge–sex standardizedAge–sex and duration of data contribution standardized
19903 118 3820.34 (0.34, 0.35)0.36 (0.36, 0.37)0.41 (0.38, 0.43)
19913 360 1310.38 (0.37, 0.38)0.40 (0.39, 0.41)0.43 (0.42, 0.44)
19923 566 9060.40 (0.40, 0.41)0.43 (0.42, 0.43)0.43 (0.42, 0.44)
19933 788 9480.43 (0.42, 0.43)0.45 (0.44, 0.46)0.48 (0.47, 0.49)
19944 021 7740.45 (0.44, 0.45)0.47 (0.46, 0.48)0.50 (0.49, 0.51)
19954 230 6290.46 (0.46, 0.47)0.49 (0.48, 0.49)0.52 (0.51, 0.54)
19964 431 7880.48 (0.47, 0.49)0.50 (0.50, 0.51)0.51 (0.51, 0.52)
19974 591 4760.50 (0.49, 0.50)0.52 (0.51, 0.52)0.55 (0.54, 0.56)
19984 693 2330.51 (0.51, 0.52)0.53 (0.53, 0.54)0.54 (0.53, 0.55)
19994 781 8980.53 (0.52, 0.53)0.55 (0.54, 0.55)0.55 (0.55, 0.56)
20004 860 6540.54 (0.54, 0.55)0.56 (0.56, 0.57)0.59 (0.58, 0.61)
20014 918 4670.56 (0.56, 0.57)0.58 (0.58, 0.59)0.62 (0.60, 0.63)
20024 952 1880.59 (0.58, 0.59)0.61 (0.60, 0.62)0.61 (0.61, 0.62)
20034 996 0920.61 (0.60, 0.61)0.63 (0.62, 0.63)0.67 (0.65, 0.68)
20045 039 3570.62 (0.62, 0.63)0.64 (0.64, 0.65)0.69 (0.68, 0.71)
20055 097 7460.64 (0.63, 0.65)0.66 (0.65, 0.67)0.76 (0.73, 0.78)
20065 096 9330.65 (0.64, 0.66)0.67 (0.66, 0.67)0.75 (0.72, 0.77)
20075 092 4820.65 (0.65, 0.66)0.67 (0.66, 0.68)0.67 (0.66, 0.68)
20085 068 3130.66 (0.65, 0.66)0.67 (0.66, 0.68)0.67 (0.67, 0.68)
20095 035 8950.66 (0.65, 0.67)0.67 (0.67, 0.68)0.67 (0.67, 0.68)
20104 946 0600.67 (0.66, 0.67)0.67 (0.67, 0.68)0.68 (0.67, 0.68)
20114 821 3770.67 (0.66, 0.67)0.67 (0.67, 0.68)0.67 (0.67, 0.68)
20124 724 8860.66 (0.66, 0.67)0.67 (0.66, 0.68)0.67 (0.67, 0.68)
20134 456 8950.66 (0.65, 0.67)0.67 (0.66, 0.67)0.67 (0.66, 0.67)
20143 966 4430.67 (0.66, 0.67)——
Mid-year prevalence of RA in the UK, 1990–2014
Fig. 2

Mid-year prevalence of RA in the UK, 1990–2014

Data given as prevalence and 95% CI. Black line, prevalence; red line, upper 95% CI estimates; blue line, lower 95% CI estimates.

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The standardized incidence of RA decreased during the study period (Table 2 and Fig. 3). On average, the incidence of RA decreased by 1.6% (95% CI 0.8, 2.5) per year from 1990 to 2014. However, there were two significant joinpoints at 1994 and 2002 (supplementary Fig. S1, available at Rheumatology Online). The incidence of RA decreased by 15.7% (95% CI 8.4, 22.4) per year between 1990 and 1994, plateaued between 1994 and 2002 with an annual change in incidence of 3.0% (95% CI − 0.5, 6.7) and again decreased by 3.8% (95% CI 1.3, 4.3) per year between 2002 and 2014. As the incidence of RA was significantly higher in 1990 and 1991, we reanalysed the data on temporal trends in the incidence of RA after excluding data from these 2 years. Even after this, there was a statistically significant reduction in the annual incidence of RA of −0.9% (95% CI − 0.1, −1.6%) per year between 1992 and 2014, and the incidence of RA decreased significantly between 2003 and 2014, with an average reduction of 2.6% (95% CI 0.6, 4.6%) per year. These findings did not change when the analysis was restricted to participants with a 3 year period of registration prior to 1 January of each year (supplementary Fig. S2, available at Rheumatology Online).
Table 2
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Incidence of RA from 1990 to 2014

YearPerson-yearsIncidence rate (95% CI) per 10 000 person-years
CrudeAge—sex standardizedaAge—sex duration of data contributed standardizeda
1990402 6277.67 (6.86, 8.58)7.81 (6.93, 8.68)7.46 (6.22, 8.70)
1991772 3765.44 (4.94, 5.98)5.73 (5.17, 6.29)6.46 (4.55, 8.37)
1992950 2894.76 (4.34, 5.22)5.01 (4.54, 5.48)4.93 (4.12, 5.75)
19931 090 6754.69 (4.30, 5.11)4.83 (4.41, 5.25)4.36 (3.75, 4.97)
19941 189 5403.94 (3.60, 4.32)4.02 (3.66, 4.39)3.85 (3.21, 4.49)
19951 303 3254.12 (3.79, 4.48)4.38 (4.00, 4.75)3.93 (2.89, 4.97)
19961 398 6903.85 (3.53, 4.19)4.02 (3.68, 4.36)3.58 (3.08, 4.08)
19971 624 1084.54 (4.23, 4.88)4.62 (4.28, 4.95)4.67 (4.11, 5.24)
19981 877 9713.98 (3.71, 4.28)4.01 (3.72, 4.30)4.22 (3.47, 4.96)
19992 210 4694.11 (3.85, 4.38)4.23 (3.95, 4.51)3.94 (3.52, 4.35)
20002 737 1964.42 (4.18, 4.68)4.61 (4.35, 4.87)4.76 (4.20, 5.32)
20013 146 1224.48 (4.26, 4.73)4.61 (4.36, 4.85)4.71 (4.22, 5.21)
20023 493 9104.64 (4.42, 4.87)4.76 (4.53, 5.00)4.64 (4.24, 5.04)
20033 751 8014.41 (4.20, 4.62)4.60 (4.37, 4.82)4.94 (4.40, 5.48)
20043 953 8374.62 (4.41, 4.84)4.80 (4.57, 5.02)5.20 (4.68, 5.72)
20054 112 5494.04 (3.85, 4.24)4.13 (3.94, 4.33)4.25 (3.86, 4.65)
20064 172 8063.92 (3.74, 4.12)3.99 (3.79, 4.18)4.18 (3.77, 4.58)
20074 185 1563.86 (3.68, 4.05)3.97 (3.78, 4.17)3.66 (3.32, 4.01)
20084 226 4543.67 (3.49, 3.86)3.78 (3.59, 3.97)3.52 (3.16, 3.87)
20094 237 6543.92 (3.73, 4.11)3.95 (3.76, 4.14)3.72 (3.39, 4.06)
20104 165 2403.72 (3.54, 3.91)3.75 (3.56, 3.93)3.52 (3.17, 3.87)
20114 076 3483.66 (3.48, 3.85)3.73 (3.54, 3.92)3.62 (3.28, 3.96)
20124 016 6323.67 (3.49, 3.87)3.76 (3.57, 3.96)3.55 (3.20, 3.90)
20133 773 0844.04 (3.84, 4.24)4.06 (3.85, 4.26)3.73 (3.38, 4.09)
20143 413 0433.81 (3.61, 4.02)——
YearPerson-yearsIncidence rate (95% CI) per 10 000 person-years
CrudeAge—sex standardizedaAge—sex duration of data contributed standardizeda
1990402 6277.67 (6.86, 8.58)7.81 (6.93, 8.68)7.46 (6.22, 8.70)
1991772 3765.44 (4.94, 5.98)5.73 (5.17, 6.29)6.46 (4.55, 8.37)
1992950 2894.76 (4.34, 5.22)5.01 (4.54, 5.48)4.93 (4.12, 5.75)
19931 090 6754.69 (4.30, 5.11)4.83 (4.41, 5.25)4.36 (3.75, 4.97)
19941 189 5403.94 (3.60, 4.32)4.02 (3.66, 4.39)3.85 (3.21, 4.49)
19951 303 3254.12 (3.79, 4.48)4.38 (4.00, 4.75)3.93 (2.89, 4.97)
19961 398 6903.85 (3.53, 4.19)4.02 (3.68, 4.36)3.58 (3.08, 4.08)
19971 624 1084.54 (4.23, 4.88)4.62 (4.28, 4.95)4.67 (4.11, 5.24)
19981 877 9713.98 (3.71, 4.28)4.01 (3.72, 4.30)4.22 (3.47, 4.96)
19992 210 4694.11 (3.85, 4.38)4.23 (3.95, 4.51)3.94 (3.52, 4.35)
20002 737 1964.42 (4.18, 4.68)4.61 (4.35, 4.87)4.76 (4.20, 5.32)
20013 146 1224.48 (4.26, 4.73)4.61 (4.36, 4.85)4.71 (4.22, 5.21)
20023 493 9104.64 (4.42, 4.87)4.76 (4.53, 5.00)4.64 (4.24, 5.04)
20033 751 8014.41 (4.20, 4.62)4.60 (4.37, 4.82)4.94 (4.40, 5.48)
20043 953 8374.62 (4.41, 4.84)4.80 (4.57, 5.02)5.20 (4.68, 5.72)
20054 112 5494.04 (3.85, 4.24)4.13 (3.94, 4.33)4.25 (3.86, 4.65)
20064 172 8063.92 (3.74, 4.12)3.99 (3.79, 4.18)4.18 (3.77, 4.58)
20074 185 1563.86 (3.68, 4.05)3.97 (3.78, 4.17)3.66 (3.32, 4.01)
20084 226 4543.67 (3.49, 3.86)3.78 (3.59, 3.97)3.52 (3.16, 3.87)
20094 237 6543.92 (3.73, 4.11)3.95 (3.76, 4.14)3.72 (3.39, 4.06)
20104 165 2403.72 (3.54, 3.91)3.75 (3.56, 3.93)3.52 (3.17, 3.87)
20114 076 3483.66 (3.48, 3.85)3.73 (3.54, 3.92)3.62 (3.28, 3.96)
20124 016 6323.67 (3.49, 3.87)3.76 (3.57, 3.96)3.55 (3.20, 3.90)
20133 773 0844.04 (3.84, 4.24)4.06 (3.85, 4.26)3.73 (3.38, 4.09)
20143 413 0433.81 (3.61, 4.02)——
a

To the 2014 population.

Table 2
Open in new tab

Incidence of RA from 1990 to 2014

YearPerson-yearsIncidence rate (95% CI) per 10 000 person-years
CrudeAge—sex standardizedaAge—sex duration of data contributed standardizeda
1990402 6277.67 (6.86, 8.58)7.81 (6.93, 8.68)7.46 (6.22, 8.70)
1991772 3765.44 (4.94, 5.98)5.73 (5.17, 6.29)6.46 (4.55, 8.37)
1992950 2894.76 (4.34, 5.22)5.01 (4.54, 5.48)4.93 (4.12, 5.75)
19931 090 6754.69 (4.30, 5.11)4.83 (4.41, 5.25)4.36 (3.75, 4.97)
19941 189 5403.94 (3.60, 4.32)4.02 (3.66, 4.39)3.85 (3.21, 4.49)
19951 303 3254.12 (3.79, 4.48)4.38 (4.00, 4.75)3.93 (2.89, 4.97)
19961 398 6903.85 (3.53, 4.19)4.02 (3.68, 4.36)3.58 (3.08, 4.08)
19971 624 1084.54 (4.23, 4.88)4.62 (4.28, 4.95)4.67 (4.11, 5.24)
19981 877 9713.98 (3.71, 4.28)4.01 (3.72, 4.30)4.22 (3.47, 4.96)
19992 210 4694.11 (3.85, 4.38)4.23 (3.95, 4.51)3.94 (3.52, 4.35)
20002 737 1964.42 (4.18, 4.68)4.61 (4.35, 4.87)4.76 (4.20, 5.32)
20013 146 1224.48 (4.26, 4.73)4.61 (4.36, 4.85)4.71 (4.22, 5.21)
20023 493 9104.64 (4.42, 4.87)4.76 (4.53, 5.00)4.64 (4.24, 5.04)
20033 751 8014.41 (4.20, 4.62)4.60 (4.37, 4.82)4.94 (4.40, 5.48)
20043 953 8374.62 (4.41, 4.84)4.80 (4.57, 5.02)5.20 (4.68, 5.72)
20054 112 5494.04 (3.85, 4.24)4.13 (3.94, 4.33)4.25 (3.86, 4.65)
20064 172 8063.92 (3.74, 4.12)3.99 (3.79, 4.18)4.18 (3.77, 4.58)
20074 185 1563.86 (3.68, 4.05)3.97 (3.78, 4.17)3.66 (3.32, 4.01)
20084 226 4543.67 (3.49, 3.86)3.78 (3.59, 3.97)3.52 (3.16, 3.87)
20094 237 6543.92 (3.73, 4.11)3.95 (3.76, 4.14)3.72 (3.39, 4.06)
20104 165 2403.72 (3.54, 3.91)3.75 (3.56, 3.93)3.52 (3.17, 3.87)
20114 076 3483.66 (3.48, 3.85)3.73 (3.54, 3.92)3.62 (3.28, 3.96)
20124 016 6323.67 (3.49, 3.87)3.76 (3.57, 3.96)3.55 (3.20, 3.90)
20133 773 0844.04 (3.84, 4.24)4.06 (3.85, 4.26)3.73 (3.38, 4.09)
20143 413 0433.81 (3.61, 4.02)——
YearPerson-yearsIncidence rate (95% CI) per 10 000 person-years
CrudeAge—sex standardizedaAge—sex duration of data contributed standardizeda
1990402 6277.67 (6.86, 8.58)7.81 (6.93, 8.68)7.46 (6.22, 8.70)
1991772 3765.44 (4.94, 5.98)5.73 (5.17, 6.29)6.46 (4.55, 8.37)
1992950 2894.76 (4.34, 5.22)5.01 (4.54, 5.48)4.93 (4.12, 5.75)
19931 090 6754.69 (4.30, 5.11)4.83 (4.41, 5.25)4.36 (3.75, 4.97)
19941 189 5403.94 (3.60, 4.32)4.02 (3.66, 4.39)3.85 (3.21, 4.49)
19951 303 3254.12 (3.79, 4.48)4.38 (4.00, 4.75)3.93 (2.89, 4.97)
19961 398 6903.85 (3.53, 4.19)4.02 (3.68, 4.36)3.58 (3.08, 4.08)
19971 624 1084.54 (4.23, 4.88)4.62 (4.28, 4.95)4.67 (4.11, 5.24)
19981 877 9713.98 (3.71, 4.28)4.01 (3.72, 4.30)4.22 (3.47, 4.96)
19992 210 4694.11 (3.85, 4.38)4.23 (3.95, 4.51)3.94 (3.52, 4.35)
20002 737 1964.42 (4.18, 4.68)4.61 (4.35, 4.87)4.76 (4.20, 5.32)
20013 146 1224.48 (4.26, 4.73)4.61 (4.36, 4.85)4.71 (4.22, 5.21)
20023 493 9104.64 (4.42, 4.87)4.76 (4.53, 5.00)4.64 (4.24, 5.04)
20033 751 8014.41 (4.20, 4.62)4.60 (4.37, 4.82)4.94 (4.40, 5.48)
20043 953 8374.62 (4.41, 4.84)4.80 (4.57, 5.02)5.20 (4.68, 5.72)
20054 112 5494.04 (3.85, 4.24)4.13 (3.94, 4.33)4.25 (3.86, 4.65)
20064 172 8063.92 (3.74, 4.12)3.99 (3.79, 4.18)4.18 (3.77, 4.58)
20074 185 1563.86 (3.68, 4.05)3.97 (3.78, 4.17)3.66 (3.32, 4.01)
20084 226 4543.67 (3.49, 3.86)3.78 (3.59, 3.97)3.52 (3.16, 3.87)
20094 237 6543.92 (3.73, 4.11)3.95 (3.76, 4.14)3.72 (3.39, 4.06)
20104 165 2403.72 (3.54, 3.91)3.75 (3.56, 3.93)3.52 (3.17, 3.87)
20114 076 3483.66 (3.48, 3.85)3.73 (3.54, 3.92)3.62 (3.28, 3.96)
20124 016 6323.67 (3.49, 3.87)3.76 (3.57, 3.96)3.55 (3.20, 3.90)
20133 773 0844.04 (3.84, 4.24)4.06 (3.85, 4.26)3.73 (3.38, 4.09)
20143 413 0433.81 (3.61, 4.02)——
a

To the 2014 population.

Annual incidence of RA in the UK, 1990–2014
Fig. 3

Annual incidence of RA in the UK, 1990–2014

Data given as incidence and 95% CI. Black line, prevalence; red line, upper 95% CI estimates; blue line, lower 95% CI estimates.

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Age-specific incidence of RA in 1994, 2004 and 2014

The peak age of onset of RA remained between 70 and 80 years of age and did not change between 1994 and 2014 (Table 3). Similar findings were observed when data from men and women were analysed separately (Table 3).

Table 3
Open in new tab

Incidence of RA by age

Age (years)Incidence rate (95% CI) per 10 000 person-years
199420042014
Overall
    <20—0.21 (0.11, 0.41)0.08 (0.03, 0.25)
    ≥20 and <300.79 (0.45, 1.39)1.09 (0.83, 1.44)0.81 (0.57, 1.16)
    ≥30 and <402.47 (1.85, 3.30)2.18 (1.82, 2.61)2.09 (1.70, 2.57)
    ≥40 and <503.82 (3.02, 4.83)3.73 (3.29, 4.22)3.48 (3.00, 4.03)
    ≥50 and <606.60 (5.41, 8.04)6.98 (6.30, 7.75)5.95 (5.30, 6.67)
    ≥60 and <707.35 (5.99, 9.00)10.44 (9.55, 11.42)7.41 (6.62, 8.29)
    ≥70 and <8010.27 (8.47, 12.45)12.08 (10.86, 13.44)10.27 (9.15, 11.53)
    ≥80 and <907.39 (5.36, 10.20)11.79 (10.30, 13.52)6.97 (5.76, 8.44)
    ≥9010.81 (5.62, 20.77)7.13 (4.55, 11.17)3.41 (1.94, 6.01)
Female
    <20—0.41 (0.20, 0.81)0.11 (0.03, 0.45)
    ≥20 and <301.09 (0.54, 2.17)1.80 (1.31, 2.46)1.26 (0.83, 1.89)
    ≥30 and <403.77 (2.71, 5.26)3.16 (2.55, 3.91)3.34 (2.65, 4.22)
    ≥40 and <505.52 (4.18, 7.28)5.81 (5.05, 6.70)4.99 (4.20, 5.94)
    ≥50 and <6010.33 (8.25, 12.93)9.33 (8.21, 10.61)8.32 (7.24, 9.55)
    ≥60 and <708.60 (6.62, 11.18)13.04 (11.65, 14.60)8.96 (7.75, 10.35)
    ≥70 and <8012.08 (9.56, 15.27)14.43 (12.65, 16.47)12.20 (10.55, 14.12)
    ≥80 and <909.01 (6.30, 12.88)14.35 (12.29, 16.75)8.50 (6.78, 10.66)
    ≥9013.85 (7.21, 26.62)7.42 (4.47, 12.31)3.24 (1.62, 6.47)
Male
    <20—0.04 (0.01, 0.32)0.05 (0.01, 0.38)
    ≥20 and <300.51 (0.19, 1.35)0.46 (0.25, 0.83)0.40 (0.20, 0.81)
    ≥30 and <401.18 (0.65, 2.12)1.24 (0.88, 1.73)0.84 (0.53, 1.34)
    ≥40 and <502.16 (1.39, 3.34)1.72 (1.33, 2.22)1.99 (1.52, 2.61)
    ≥50 and <602.93 (1.93, 4.46)4.70 (3.94, 5.62)3.63 (2.96, 4.47)
    ≥60 and <706.02 (4.36, 8.30)7.81 (6.75, 9.04)5.82 (4.86, 6.98)
    ≥70 and <807.85 (5.61, 10.98)9.25 (7.72, 11.09)8.11 (6.71, 9.80)
    ≥80 and <904.18 (1.99, 8.77)7.35 (5.52, 9.78)4.81 (3.36, 6.88)
    ≥90—6.21 (2.33, 16.53)3.82 (1.43, 10.18)
Age (years)Incidence rate (95% CI) per 10 000 person-years
199420042014
Overall
    <20—0.21 (0.11, 0.41)0.08 (0.03, 0.25)
    ≥20 and <300.79 (0.45, 1.39)1.09 (0.83, 1.44)0.81 (0.57, 1.16)
    ≥30 and <402.47 (1.85, 3.30)2.18 (1.82, 2.61)2.09 (1.70, 2.57)
    ≥40 and <503.82 (3.02, 4.83)3.73 (3.29, 4.22)3.48 (3.00, 4.03)
    ≥50 and <606.60 (5.41, 8.04)6.98 (6.30, 7.75)5.95 (5.30, 6.67)
    ≥60 and <707.35 (5.99, 9.00)10.44 (9.55, 11.42)7.41 (6.62, 8.29)
    ≥70 and <8010.27 (8.47, 12.45)12.08 (10.86, 13.44)10.27 (9.15, 11.53)
    ≥80 and <907.39 (5.36, 10.20)11.79 (10.30, 13.52)6.97 (5.76, 8.44)
    ≥9010.81 (5.62, 20.77)7.13 (4.55, 11.17)3.41 (1.94, 6.01)
Female
    <20—0.41 (0.20, 0.81)0.11 (0.03, 0.45)
    ≥20 and <301.09 (0.54, 2.17)1.80 (1.31, 2.46)1.26 (0.83, 1.89)
    ≥30 and <403.77 (2.71, 5.26)3.16 (2.55, 3.91)3.34 (2.65, 4.22)
    ≥40 and <505.52 (4.18, 7.28)5.81 (5.05, 6.70)4.99 (4.20, 5.94)
    ≥50 and <6010.33 (8.25, 12.93)9.33 (8.21, 10.61)8.32 (7.24, 9.55)
    ≥60 and <708.60 (6.62, 11.18)13.04 (11.65, 14.60)8.96 (7.75, 10.35)
    ≥70 and <8012.08 (9.56, 15.27)14.43 (12.65, 16.47)12.20 (10.55, 14.12)
    ≥80 and <909.01 (6.30, 12.88)14.35 (12.29, 16.75)8.50 (6.78, 10.66)
    ≥9013.85 (7.21, 26.62)7.42 (4.47, 12.31)3.24 (1.62, 6.47)
Male
    <20—0.04 (0.01, 0.32)0.05 (0.01, 0.38)
    ≥20 and <300.51 (0.19, 1.35)0.46 (0.25, 0.83)0.40 (0.20, 0.81)
    ≥30 and <401.18 (0.65, 2.12)1.24 (0.88, 1.73)0.84 (0.53, 1.34)
    ≥40 and <502.16 (1.39, 3.34)1.72 (1.33, 2.22)1.99 (1.52, 2.61)
    ≥50 and <602.93 (1.93, 4.46)4.70 (3.94, 5.62)3.63 (2.96, 4.47)
    ≥60 and <706.02 (4.36, 8.30)7.81 (6.75, 9.04)5.82 (4.86, 6.98)
    ≥70 and <807.85 (5.61, 10.98)9.25 (7.72, 11.09)8.11 (6.71, 9.80)
    ≥80 and <904.18 (1.99, 8.77)7.35 (5.52, 9.78)4.81 (3.36, 6.88)
    ≥90—6.21 (2.33, 16.53)3.82 (1.43, 10.18)
Table 3
Open in new tab

Incidence of RA by age

Age (years)Incidence rate (95% CI) per 10 000 person-years
199420042014
Overall
    <20—0.21 (0.11, 0.41)0.08 (0.03, 0.25)
    ≥20 and <300.79 (0.45, 1.39)1.09 (0.83, 1.44)0.81 (0.57, 1.16)
    ≥30 and <402.47 (1.85, 3.30)2.18 (1.82, 2.61)2.09 (1.70, 2.57)
    ≥40 and <503.82 (3.02, 4.83)3.73 (3.29, 4.22)3.48 (3.00, 4.03)
    ≥50 and <606.60 (5.41, 8.04)6.98 (6.30, 7.75)5.95 (5.30, 6.67)
    ≥60 and <707.35 (5.99, 9.00)10.44 (9.55, 11.42)7.41 (6.62, 8.29)
    ≥70 and <8010.27 (8.47, 12.45)12.08 (10.86, 13.44)10.27 (9.15, 11.53)
    ≥80 and <907.39 (5.36, 10.20)11.79 (10.30, 13.52)6.97 (5.76, 8.44)
    ≥9010.81 (5.62, 20.77)7.13 (4.55, 11.17)3.41 (1.94, 6.01)
Female
    <20—0.41 (0.20, 0.81)0.11 (0.03, 0.45)
    ≥20 and <301.09 (0.54, 2.17)1.80 (1.31, 2.46)1.26 (0.83, 1.89)
    ≥30 and <403.77 (2.71, 5.26)3.16 (2.55, 3.91)3.34 (2.65, 4.22)
    ≥40 and <505.52 (4.18, 7.28)5.81 (5.05, 6.70)4.99 (4.20, 5.94)
    ≥50 and <6010.33 (8.25, 12.93)9.33 (8.21, 10.61)8.32 (7.24, 9.55)
    ≥60 and <708.60 (6.62, 11.18)13.04 (11.65, 14.60)8.96 (7.75, 10.35)
    ≥70 and <8012.08 (9.56, 15.27)14.43 (12.65, 16.47)12.20 (10.55, 14.12)
    ≥80 and <909.01 (6.30, 12.88)14.35 (12.29, 16.75)8.50 (6.78, 10.66)
    ≥9013.85 (7.21, 26.62)7.42 (4.47, 12.31)3.24 (1.62, 6.47)
Male
    <20—0.04 (0.01, 0.32)0.05 (0.01, 0.38)
    ≥20 and <300.51 (0.19, 1.35)0.46 (0.25, 0.83)0.40 (0.20, 0.81)
    ≥30 and <401.18 (0.65, 2.12)1.24 (0.88, 1.73)0.84 (0.53, 1.34)
    ≥40 and <502.16 (1.39, 3.34)1.72 (1.33, 2.22)1.99 (1.52, 2.61)
    ≥50 and <602.93 (1.93, 4.46)4.70 (3.94, 5.62)3.63 (2.96, 4.47)
    ≥60 and <706.02 (4.36, 8.30)7.81 (6.75, 9.04)5.82 (4.86, 6.98)
    ≥70 and <807.85 (5.61, 10.98)9.25 (7.72, 11.09)8.11 (6.71, 9.80)
    ≥80 and <904.18 (1.99, 8.77)7.35 (5.52, 9.78)4.81 (3.36, 6.88)
    ≥90—6.21 (2.33, 16.53)3.82 (1.43, 10.18)
Age (years)Incidence rate (95% CI) per 10 000 person-years
199420042014
Overall
    <20—0.21 (0.11, 0.41)0.08 (0.03, 0.25)
    ≥20 and <300.79 (0.45, 1.39)1.09 (0.83, 1.44)0.81 (0.57, 1.16)
    ≥30 and <402.47 (1.85, 3.30)2.18 (1.82, 2.61)2.09 (1.70, 2.57)
    ≥40 and <503.82 (3.02, 4.83)3.73 (3.29, 4.22)3.48 (3.00, 4.03)
    ≥50 and <606.60 (5.41, 8.04)6.98 (6.30, 7.75)5.95 (5.30, 6.67)
    ≥60 and <707.35 (5.99, 9.00)10.44 (9.55, 11.42)7.41 (6.62, 8.29)
    ≥70 and <8010.27 (8.47, 12.45)12.08 (10.86, 13.44)10.27 (9.15, 11.53)
    ≥80 and <907.39 (5.36, 10.20)11.79 (10.30, 13.52)6.97 (5.76, 8.44)
    ≥9010.81 (5.62, 20.77)7.13 (4.55, 11.17)3.41 (1.94, 6.01)
Female
    <20—0.41 (0.20, 0.81)0.11 (0.03, 0.45)
    ≥20 and <301.09 (0.54, 2.17)1.80 (1.31, 2.46)1.26 (0.83, 1.89)
    ≥30 and <403.77 (2.71, 5.26)3.16 (2.55, 3.91)3.34 (2.65, 4.22)
    ≥40 and <505.52 (4.18, 7.28)5.81 (5.05, 6.70)4.99 (4.20, 5.94)
    ≥50 and <6010.33 (8.25, 12.93)9.33 (8.21, 10.61)8.32 (7.24, 9.55)
    ≥60 and <708.60 (6.62, 11.18)13.04 (11.65, 14.60)8.96 (7.75, 10.35)
    ≥70 and <8012.08 (9.56, 15.27)14.43 (12.65, 16.47)12.20 (10.55, 14.12)
    ≥80 and <909.01 (6.30, 12.88)14.35 (12.29, 16.75)8.50 (6.78, 10.66)
    ≥9013.85 (7.21, 26.62)7.42 (4.47, 12.31)3.24 (1.62, 6.47)
Male
    <20—0.04 (0.01, 0.32)0.05 (0.01, 0.38)
    ≥20 and <300.51 (0.19, 1.35)0.46 (0.25, 0.83)0.40 (0.20, 0.81)
    ≥30 and <401.18 (0.65, 2.12)1.24 (0.88, 1.73)0.84 (0.53, 1.34)
    ≥40 and <502.16 (1.39, 3.34)1.72 (1.33, 2.22)1.99 (1.52, 2.61)
    ≥50 and <602.93 (1.93, 4.46)4.70 (3.94, 5.62)3.63 (2.96, 4.47)
    ≥60 and <706.02 (4.36, 8.30)7.81 (6.75, 9.04)5.82 (4.86, 6.98)
    ≥70 and <807.85 (5.61, 10.98)9.25 (7.72, 11.09)8.11 (6.71, 9.80)
    ≥80 and <904.18 (1.99, 8.77)7.35 (5.52, 9.78)4.81 (3.36, 6.88)
    ≥90—6.21 (2.33, 16.53)3.82 (1.43, 10.18)

Geographic variation in 2014

There were statistically significant differences in the prevalence and incidence of RA throughout the UK (P < 0.001), supplementary Fig. S3, available at Rheumatology Online. The age–sex standardized prevalence of RA was highest in the North East, Yorkshire and Humber and Northern Ireland. Regions with the lowest prevalence of RA were South Central and London. The East Midlands, Yorkshire and Humber and South West were the regions with the highest standardized incidence of RA, while North East, West Midlands and Wales had the lowest incidence.

Discussion

This is the largest study to examine temporal trends in the incidence and prevalence of RA. It reports an increase in the point prevalence of RA from 1990 to 2005, but a subsequent reduction between 2005 and 2014, and a gradual reduction in its incidence over time. It also reports that the peak age of incidence of RA is in the eighth decade of life, which has not changed over the past 20 years. In addition, this study found evidence of significant geographic variation in the incidence and prevalence of RA in the UK.

There was an increase in the prevalence of RA from 1990 to 2005, but not in subsequent years. This finding is contrary to that of a Global Burden of Diseases study that reported the prevalence of RA remained unchanged between 1990 and 2010 [26]. However, that was a systematic review of published studies, which would have different observation periods for each study, hence it would be difficult to determine the temporal change. This contrasts with studies from Ontario, Canada [27], and Rochester, NY, USA [13], where the prevalence of RA increased over time, with no reduction in recent years. Further research is required to explore factors underlying this, but this could include migration and mortality. Findings from several recent studies demonstrate that the standardized mortality rate in RA has not improved over time despite improvements in the treatment of RA [28–30].

In our study, the incidence of RA decreased over time. However, it was significantly higher in 1990 and 1991 compared with later years despite our taking precautions to prevent prevalent cases being classified as incident cases by requiring participants to have 12 months of registration prior to being coded as having incident RA. We also undertook a sensitivity analysis by specifying a 3 year prior registration period before a participant could be coded to have incident RA. The latter approach did not reduce the significantly higher incidence rate in 1990 and 1991. Thus we are reasonably certain that the high incidence rate in 1990 and 1991 is not related to prevalent RA cases being more likely to be coded as incident RA in the early years of the CPRD.

We observed an increase in the incidence of RA in the early 2000s. This could be explained by the increasing availability of anti-CCP antibody testing in the UK, which allowed cases previously coded as having seronegative inflammatory arthritis or inflammatory arthritis to be coded as RA [31]. Similarly, the initial National Institute for Health and Care Excellence approval for use of anti-TNF treatments in patients with RA in the year 2000 could have prompted rheumatologists to better classify their patients.

It is noteworthy that the recent 2010 ACR/EULAR criteria for the classification of RA did increase the incidence of RA [32]. The 2010 ACR/EULAR classification criteria allow patients to be classified as RA at an earlier, less severe stage than the 1987 ACR criteria [33] and allow a greater number of patients with unclassified inflammatory arthritis to meet the classification criteria for RA [34]. This finding suggests that either the incidence of RA has decreased more significantly, and is being masked by a change in disease classification criteria, or that physicians are slow to adapt to changes in nomenclature and classification systems. We do not believe that the reduction in the incidence of RA over time is due to the exclusion of previous incident cases, as this phenomenon would have resulted in a reduction in the incidence of other diseases such as gout [35] and type 2 diabetes for which the incidence in the CPRD has remained stable and risen, respectively [36].

RA is a common complex disease where genetic predisposition (shared epitope [37]), constitutional risk factors (obesity [38]) and environmental exposures (smoking) interact to cause chronic joint inflammation [39]. As the genetic makeup of a population does not change over relatively short periods of time, and the prevalence of obesity is increasing [5], the reduction in the incidence of RA could be related to reducing the prevalence of cigarette smoking in the UK. The prevalence of cigarette smoking in the UK decreased from 45% in 1974 to 19% in 2013, with similar reductions in both men and women [40]. The fact that reducing incidence of RA may be related to smoking is further supported by the fact that areas with a high prevalence of cigarette smoking have a high prevalence of RA, and vice versa. For example, North East of England, Yorkshire and Humber, Scotland and Wales have a high prevalence both of RA and cigarette smoking, while South Central, London and East of England have a lower prevalence of RA and of cigarette smoking [41]. However, geographic variation in the prevalence of RA could be related to other aetiological changes such as socio-economic deprivation that also co-associate with smoking [42].

This study provides contemporary data on the epidemiology of RA. The prevalence and incidence of RA in the UK and the female predominance reported in this study are in accord with the findings of previous epidemiological studies and provide external validity for these findings. We standardized the crude incidence and prevalence of RA to the 2014 population structure and also to the number of years for which data were contributed prior to 1 January or 1 July of that year. This reduces the possibility of confounding due to changes in population structure over time and events occurring prior to the start of the study period. Thus we are reasonably confident that the reduction in the incidence of RA over time is a valid finding.

The main limitations of this study are those inherent in the use of a large consultation-based database such as the CPRD. However, the accuracy of the diagnosis of RA has been validated previously, which minimizes the possibility of an incorrect diagnosis. The index date reflects the date of allocation of Read codes for RA and does not reflect disease onset or the date of diagnosis. However, the date of allocation of a Read code for RA (which may happen after a hospital letter confirming a diagnosis of RA) would be expected to be within a few months of the date of diagnosis and does not invalidate the findings on the temporal trends in the epidemiology of RA over a 25 year period. We modified the published Read code list for identifying RA cases to increase its face validity. However, we did not perform a sensitivity analysis to examine the effects of these changes on the results. We do not think a change in the Read code list will alter the findings on temporal trends in the epidemiology of RA.

In summary, the incidence of RA in the UK is decreasing. These data confirm the known predilection of RA in women, but contrary to general opinion, the peak age of diagnosis of RA is in later years. There was UK-wide variation in the incidence and prevalence of RA and further research is required to identify the reasons underlying this phenomenon. Further research is also required to examine temporal trends in mortality of RA and to determine if the reduction in the incidence of RA is due to the reduced prevalence of cigarette smoking.

Acknowledgements

A.A., M.D., W.Z., C.F.-K. and C.M. conceptualized the study. Data analysis was performed by A.A. and supervised by W.Z. and M.G. C.F.-K. drew the choropleth maps. All authors read and approved the final version of the manuscript for submission. M.G. is the overall guarantor of the research. All authors, external and internal, had full access to all of the data (including statistical reports and tables) in the study and take responsibility for the integrity of the data and the accuracy of the data analysis.

Funding: A.A., M.D., W.Z., and M.J.G. are funded by the University of Nottingham, Nottingham, UK. C.D.M. is funded by the National Institute for Health Research (NIHR) Collaborations for Leadership in Applied Health Research and Care West Midlands, the NIHR School for Primary Care Research and an NIHR Research Professorship in General Practice (NIHR-RP-2014-04-026). This article presents independent research funded by the University of Nottingham and NIHR. The views expressed are those of the authors and not necessarily those of the National Health Service, the NIHR or the Department of Health.

Disclosure statement: W.Z. reports grants from Arthritis Research UK during the conduct of the study and honoraria from AstraZeneca for consultation on lesinurad, Daiichi Sankyo, Biobarica and Hisun as an invited speaker outside the submitted work. All other authors have declared no conflicts of interest.

Supplementary data

Supplementary data are available at Rheumatology Online.

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