Rheumatology International

, Volume 34, Issue 7, pp 909–917

Prevalence and incidence of systemic lupus erythematosus in South Korea

Authors

  • Jee-Seon Shim
    • Department of RheumatologyHanyang University Hospital for Rheumatic Diseases
  • Yoon-Kyoung Sung
    • Department of RheumatologyHanyang University Hospital for Rheumatic Diseases
  • Young Bin Joo
    • Department of RheumatologyHanyang University Hospital for Rheumatic Diseases
  • Hye-Soon Lee
    • Department of RheumatologyHanyang University Hospital for Rheumatic Diseases
    • Department of RheumatologyHanyang University Hospital for Rheumatic Diseases
Original Article

DOI: 10.1007/s00296-013-2915-9

Cite this article as:
Shim, J., Sung, Y., Joo, Y.B. et al. Rheumatol Int (2014) 34: 909. doi:10.1007/s00296-013-2915-9

Abstract

The aim of this study was to estimate the nationwide prevalence and incidence of systemic lupus erythematosus (SLE) in South Korea. National Health Insurance claims data covering almost all Koreans (~50 million) during 2006–2010 were analyzed. Individuals with SLE were identified if (1) they had experienced at least one hospitalization for SLE (International Classification of Diseases, 10th revision code M32), (2) they had taken at least one concomitant prescription of immunosuppressant and hydroxychloroquine, or (3) they had taken anti-dsDNA antibody (≥2) or complement tests (≥2) during each calendar year. Incident cases were defined only if they had not been SLE prevalent for the preceding 2 years and had been SLE prevalent for 2 years consecutively thereafter. The annual prevalence (per 100,000) increased slightly from 20.6 [95 % confidence interval (95 % CI) 20.2–21.0] in 2006 to 26.5 (95 % CI 26.0–27.0) in 2010, and the incidence (per 100,000) ranged between 2.5 (95 % CI 2.4–2.6) in 2008 and 2.8 (95 % CI 2.7–2.9) in 2009. The number of SLE-prevalent female patients outnumbered SLE-prevalent male patients by approximately sixfold, with a female-to-male incidence ratio of ~9:1. The prevalence and incidence of SLE increased significantly with age, regardless of sex, to a peak the age of 30–39 years. However, while both of them significantly decreased thereafter in females, this tendency was not observed in males.

Keywords

PrevalenceIncidenceSystemic lupus erythematosusKorea

Introduction

Systemic lupus erythematosus (SLE) is a chronic autoimmune disorder that may affect diverse organ systems, and for which clinical manifestations tend to accrue gradually over time [1]. There have been tremendous improvements in diagnosis and medical care for SLE since the 1950s, including earlier diagnosis, dialysis, renal replacement, and medication, resulting in an increase in the 5-year survival rate from 50 % to over 90 %, and in the 15- to 20-year survival rate of up to around 80 % [2, 3]. However, SLE still carries with it a significantly higher risk of death than for the general population and, as the patients survive longer, they face a range of complications from the disease itself or from damage consequent to its treatment during their lifetime [4]. SLE also reduces the patient’s health-related quality of life, incurs high medical costs and significant productivity loss, and represents a great burden to both society and the patient [5, 6].

The etiology of SLE has not yet been fully described, but it has been shown that both the magnitude and severity of the disease differ markedly with respect to sex, age, race, and region [3, 7]. In the USA, the prevalence and incidence of SLE are 100–150 (per 100,000) and over 5 (per 100,000), respectively [812], and SLE is more predominant among African Americans, Asians, Native Americans, and Hispanics than in Whites [11, 13]. In Norway and the UK, SLE also occurs more frequently in Asians than in Europeans [14, 15]. A recent review of the epidemiology of SLE in the Asia–Pacific region found that the prevalence and incidence ranged from 4.3 to 45.3 (per 100,000) and from 0.9 to 3.1 (per 100,000), respectively [16]. Epidemiologic information regarding SLE in South Korea has yet to be reported.

The aim of the present study was to estimate the nationwide prevalence and incidence of SLE using Korean National Health Insurance (NHI) claims data.

Materials and methods

Data source

A mandatory universal health insurance system has been operating in South Korea since 1989, and in 2010, about 50 million people were covered by the NHI program [17]. NHI claims data contain nationwide medical information, including outpatient claims, inpatient claims, and details of both procedures and prescriptions. Claims data are collected for reimbursement. The NHI has healthcare service claims submitted by service providers and thus does not have the results of laboratory examinations. Almost all of these data are collected through an electronic claiming system, and all information is managed by the Health Insurance Research and Assessment Agency (HIRA), which is affiliated to the National Health Insurance Corporation (NHIC).

The present study used all claims records of enrollees aged 1–99 years from the Korean NHI claims database between January 1, 2006 and December 31, 2010. This study was approved by the Care Record Supply Committee of the HIRA. Since personal identification numbers in the claims data were encoded so as to ensure the anonymity of the enrollees, the study protocol did not require approval from an institutional review board.

Identification of SLE cases

Given that the diagnostic accuracy of the claims data may be questionable, SLE cases were identified based on an operational definition rather than solely on the diagnostic codes. Using the 2010 data, algorithms were developed with a view to identifying SLE cases; the best of these was chosen after evaluating their accuracy.

First, several SLE-related characteristics were chosen through rheumatologists’ reviews, including hospitalization due to SLE, prescription (hydroxychloroquine, immunosuppressants, and steroids), and laboratory examinations [anti-dsDNA antibody test and complement test (C3 or C4)]. After confirming whether enrollees had claim issues related to these individual characteristics during the calendar year (January 1–December 31), all information regarding the presence of hospitalization, prescriptions, and laboratory tests was combined to make several algorithms for identifying SLE cases. Their accuracy was evaluated through comparing the number of algorithm-identified cases to that of true cases with SLE. Patients who were registered in the Individual Copayment Beneficiaries Program (ICBP) for rare and intractable disorders were defined as true cases with SLE. The ICBP is an individual copayment beneficiaries program for patients with rare and intractable disease to reduce their burden of medical expenses [18] Application for registration with this program is made on behalf of patients by their doctor; patients must fulfill at least four of the 1997 revised American College of Rheumatology (ACR) classification criteria [19]. Registration of SLE patients who meet these criteria only began in July 2009. However, since the registration system was in its early days, true SLE patients might have been included as non-SLE cases during that first year if their doctors did not register them with the ICBP due to unawareness of the system. Therefore, only data from 2010 were used to develop and evaluate the accuracy of the algorithms, and all claims issued from medical institutions from which no SLE patients had been registered with the ICBP during the study period were excluded.

We calculated comparability ratio, sensitivity, specificity, accuracy, predictive positive value (PPV), and negative predictive value (NPV) of all algorithms as well as each single SLE-related characteristic. Comparability ratio is a ratio of the number of algorithm-identified SLE cases to that of true SLE cases. Ratio over 1.0 means that algorithm-identified cases were much more than true cases. When ratio is close to 1.0, the number of algorithm-identified cases is similar to that of true SLE case.

A total of 32,058 enrollees had at least one claim issued with a diagnostic code of SLE in 2010. Of these, 41.9 % (13,421) were registered with the ICBP. Table 1 gives the validity of each single SLE-related characteristic and algorithms in combination of these single characteristics. Of the SLE-related characteristics, hospitalization due to SLE appeared to be less sensitive for identifying SLE and tended to underestimate the number of cases compared to the other characteristics. With respect to SLE-related treatment, concomitant prescription of two or more drugs was more specific and accurate. However, laboratory tests were both more accurate and more sensitive than concomitant prescriptions. Among algorithms in combination of SLE-related characteristics, that with the lowest possibility of overestimation and underestimation of SLE cases, but with the highest sensitivity, specificity, and accuracy was chosen.
Table 1

Validity of each single SLE-related characteristic and algorithms combined with SLE-related characteristics

(Number of claims)

Comparability ratio

Accuracy (%)

Sensitivity (%)

Specificity (%)

PPV (%)

NPV (%)

Each single SLE-related characteristic

 Hospitalization (≥1)

0.4

60

22

88

57

61

 Prescription (≥1)

  Immunosuppressant

0.4

69

33

95

83

66

  HCQ

1.0

76

73

78

70

80

  Steroid

1.2

73

76

71

65

81

 Concomitant prescription (≥1)

  Immunosuppressant and steroid

0.4

68

30

96

85

66

  Immunosuppressant and HCQ

0.2

66

21

98

90

63

  Steroid and HCQ

0.7

74

56

87

76

73

 Laboratory examination (≥2)

  Complement test (C3 or C4)

0.7

82

64

94

89

79

  Anti-dsDNA antibody test

0.6

79

58

95

89

76

Combined algorithms

 Hospitalization (≥1), or immunosuppressant and HCQ (≥1)

0.5

65

36

87

66

65

 Hospitalization (≥1), or immunosuppressant and HCQ (≥1), or complement (C3 or C4) test (≥2)

1.0

78

72

83

75

81

 Hospitalization (≥1), or immunosuppressant and HCQ (≥1), or anti-dsDNA antibody test (≥2)

0.9

77

69

83

75

79

 Hospitalization (≥1), or immunosuppressant and HCQ (≥1), or complement (C3 or C4) test (≥2), or anti-dsDNA antibody test (≥2)

1.0

79

74

82

75

81

PPV positive predictive value, NPV negative predictive value, C3 complement 3, C4 complement 4, HCQ hydroxychloroquine

The best algorithm combined the presence of (1) hospitalization for SLE (International Classification of Diseases, 10th revision, ICD-10, code M32), (2) concomitant prescription of immunosuppressant and hydroxychloroquine, or (3) examination of anti-dsDNA antibody (≥2) or complement test (≥2) during each calendar year. The comparability ratio, accuracy, sensitivity, specificity, and positive and negative predictive values were 1.0, 79, 74, 82, 75, and 81 %, respectively.

Estimation of prevalence and incidence

All claims data during 2006–2010 were used to identify prevalent and incident SLE cases. According to the selected algorithm, subjects were identified as SLE-prevalent cases each year if they had experienced at least one hospitalization with a diagnostic code for SLE (ICD-10 diagnostic code M32), taken concomitant prescription of immunosuppressant and hydroxychloroquine (≥1), or taken anti-dsDNA antibody (≥2) or complement tests (C3 or C4, ≥2) during the calendar year. Incident cases of SLE were identified during 2008–2009. We defined subjects who had no SLE for the preceding 2 years (e.g., 2006–2007) and met the algorithm in the year (e.g., 2008) and also in the following year (e.g., 2009) as incident cases in the year (e.g., 2008).

For annual prevalence, the year-specific numerator was subjects who were prevalent cases in the specific calendar year, and the denominator was the mid-year population from the Korean National Statistical Office of the year. For annual incidence, the year-specific numerator was subjects who were incident cases in the specific calendar year and the denominator was same as for the calculation of prevalence.

Crude rates, sex- and age-specific rates, standardized rates adjusted for sex and age using the 2008 mid-year population, and their 95 % confidence intervals (95 % CIs) were calculated. The crude rates did not differ from the standardized rates, and so they are not presented herein. All analyses were conducted with SAS 9.1.2 Statistical Software (SAS Institute, Cary, NC, USA).

Results

There were 10,080 prevalent SLE patients (1,339 males, 8,741 females) in 2006. The magnitude of prevalent SLE increased to 13,316 patients (1,914 males, 11,402 females) in 2010. The overall SLE prevalence (per 100,000) increased significantly each year, from 20.6 (95 % CI 20.2–21.0) in 2006 to 26.5 (95 % CI 26.0–27.0) in 2010 (Table 2). The prevalence differed significantly with sex. In 2010, 45.8 per 100,000 females and 7.5 per 100,000 males had SLE. On the whole, there were about sixfold more SLE-prevalent female than male patients. The prevalence of SLE was also different according to age (Fig. 1). The overall prevalence increased significantly with age, peaking in the age group of 30–39 years, and then decreased significantly thereafter. While the trend among females was similar to the overall prevalence, it was different for males, for who the prevalence increased until the age group of 30–39 years, as for the females, but then plateaued thereafter (Fig. 1; Supplement Table 1).
Table 2

Prevalence and incidence of SLE in South Korea (2006–2010)

 

Overall

Male

Female

No. of cases

Rate per 105 (95 % CI)

No. of cases

Rate per 105 (95 % CI)

No. of cases

Rate per 105 (95 % CI)

Prevalence

 2006

10,080

20.6 (20.2–21.0)

1,339

5.5 (5.2–5.8)

8,741

35.7 (35.0–36.4)

 2007

10,771

21.9 (21.5–22.3)

1,538

6.3 (6.0–6.6)

9,233

37.6 (36.8–38.4)

 2008

11,609

23.5 (23.1–23.9)

1,812

7.3 (7.0–7.6)

9,797

39.7 (38.9–40.5)

 2009

12,351

24.9 (24.5–25.3)

1,739

7.0 (6.7–7.3)

10,612

42.9 (42.1–43.7)

 2010

13,316

26.5 (26.0–27.0)

1,914

7.5 (7.2–7.8)

11,402

45.8 (45.0–46.6)

Incidence

 2008

1,260

2.5 (2.4–2.6)

117

0.5 (0.4–0.6)

1,143

4.6 (4.3–4.9)

 2009

1,398

2.8 (2.7–2.9)

148

0.6 (0.5–0.7)

1,250

5.1 (4.8–5.4)

Rates adjusted for age and sex using data from the 2008 mid-year population from the Korean National Statistical Office

https://static-content.springer.com/image/art%3A10.1007%2Fs00296-013-2915-9/MediaObjects/296_2013_2915_Fig1_HTML.gif
Fig. 1

Prevalence (a) and incidence (b) of SLE in 2008, stratified according to sex and age group

The overall incidence (per 100,000) was 2.5 (95 % CI 2.4–2.6) in 2008 and 2.8 (95 % CI 2.7–2.9) in 2009 (Table 2). There were 1,260 incident cases (117 males, 1,143 females) in 2008, and the female-to-male ratio was about 9:1. As with prevalence, the incidence increased significantly with age until 30–39 years and then decreased slowly thereafter; while this trend was observed among females, it was not obvious for males (Fig. 1; Supplement Table 2).

Discussion

Although numerous studies on SLE prevalence and incidence have been conducted in various regions of the world, SLE burden in South Korea has not yet been reported. This study estimated the nationwide prevalence and incidence of SLE in South Korea using NHI claims data that included almost all Koreans. The prevalence of SLE (per 100,000) was from 20.6 in 2006 to 26.5 in 2010 and tended to slightly increase each year. The incidence of SLE (per 100,000) ranged from 2.5 in 2008 to 2.8 in 2009.

It has been reported that the prevalence of SLE is generally higher in America—including the USA [812, 20, 21], Canada [22, 23], and Puerto Rico [24]—than elsewhere, ranging from 100 to 150 per 100,000 people (Table 3; Fig. 2). With the exception of Taiwan (97.5 per 100,000), the prevalence across Asian countries is 30–50 per 100,000 peoples [2529], and in Europe, the prevalence ranges from 20 to 70 per 100,000 people [3037]. The prevalence in the present study was slightly lower than reported for both China (31.1–46.5 per 100,000) and Japan (7.0 per 100,000 males, 68.4 per 100,000 females). In the present study, SLE was about sixfold more prevalent in females than in males. The female-to-male ratio in this population was generally similar to other studies, ranged from ~5:1 to ~10:1 [10, 11, 14, 22, 29, 32, 34, 37]. The ratio tends to increase with age to peak during the childbearing ages, declining slowly thereafter [14, 28, 32, 37]. The prevalence of SLE in South Korea and Taiwan was highest in the 30–39 years, while in the UK and Norway, it is highest at 50–59 and 60–69 years, respectively [14, 28, 32].
Table 3

Studies on the prevalence and incidence of SLE in other countries

References

Country (area)

Period

Data source

Age (years)

No. of prevalent cases

Prevalence per 105

Incidence per 105

Hochberg et al. [8]

USA

NS

Telephone survey

≥18

15

124a

NS

Uramoto et al. [9]

USA (MN)

1950–1992

Medical records

NS

48

122b

5.56b

Ward [20]

USA

1988–1994

Nationwide survey

≥17

12c

53.6c

NS

Naleway et al. [21]

USA (WI)

1991–2001

Medical records

≥0

117

78.5

5.1

Chakravarty et al. [10]

USA (CA, PA)

2000

Hospitalization data

≥18

532

107.6 (CA)

149.5 (PA)

NS

Feldman et al. [11]

USA

2000–2004

Medicaid claims data

18–65

34,339

143.7

23.2

Furst et al. [12]

USA

2003–2008

MCPs claims data

≥18

15,396

102.9d

7.2

Barnabe et al. [22]

Canada (Alberta)

1994–2007

Claims, hospitalization data

NS

10,390

32 (male)

273 (female)

NS

Peschken and Esdaile [23]

Canada (Manitoba)

1980–1996

Medical records

≥0

257

42.3 (NAI)

20.6 (non-NAI)

NS

Molina et al. [24]

Puerto Rico

2003

Private health insurance data

NS

877

159

NS

Xiang and Dai [25]

China

NS

NS

≥18

NS

37.7 (Shanghai)e

NS

Zeng et al. [26]

China

NS

NS

21–40

≥20

NS

31.1 (Guangzhou)f

46.5 (Shangdong)f

NS

Mok et al. [27]

Hong Kong

2000–2006

Hospital records

NS

442

NS

3.1

Yeh et al. [28]

Taiwan

2003–2008

NHIRD

>0

6,675

97.5

4.87

Iseki et al. [29]

Japan (Okinawa)

1972–1991

Hospital records

≥0

566

7.0 (male)g

68.4 (female)g

0.8 (male)g

4.7 (female)g

Hopkinson et al. [30]

UK (Nottingham)

1989–1990

Hospital records

NS

147

24.6

4.0

Johnson et al. [31]

UK (Birmingham)

1991–1992

Hospital records

 

242

27.7

3.8

Nightingale et al. [32, 38]

UK

UK

1992–1998

1992–1998

GPRD

GPRD

>0

>0

1,538

390

40.7

NS

NS

3.0

Lerang et al. [14]

Norway (Oslo)

1999–2008

Hospital records

≥16

238

51.8

3.0

Stahl-Hallengren et al. [33]

Sweden

1981–1991

Hospital records

>15

379h

68.0h

4.8h

Alonso et al. [34]

Spain

1987–2006

Medical records

≥15

150

17.5

3.6

Laustrup et al. [35]

Denmark

1995–2003

Medical records, interview

≥15

109i

28.3i

1.04i

Govoni et al. [36]

Italy

1996–2002

Hospital discharge data

≥16

201

57.9

2.6j

Alamanos et al. [37]

Greece

1981–2001

Medical records

NS

178

39.5k

2.1k

WI Wisconsin, MN Minnesota, CA California, PA Pennsylvania, NS not specified, MCPs managed-care plans, NAI North American Indians, NHIRD National Health Insurance Research Data, GPRD, General Practice Research Data

aEstimates based on validated SLE by reviewing medical records; if just self-reported physician diagnosis, the prevalence was 372

bPrevalence in 1993 and incidence during 1980–1992

cEstimates based on treated SLE with medication; if self-reported physician diagnosis, the number of cases and prevalence were 40 and 241, respectively

dPrevalence in 2008; in 2003 the prevalence was 81.1

eReported estimate after correction for the sex bias of the result from the original report

fEstimates of Guangzhou in 1989 and Shangdong in 1997

gEstimates in 1991

hEstimates of SLE patients and prevalence in 1991, incidence in 1987–1991

iEstimates in 2002, which were based on definite SLE cases classified by ACR criteria

jEstimates in 2002

kPrevalence in 2001 and incidence in 1997–2001

https://static-content.springer.com/image/art%3A10.1007%2Fs00296-013-2915-9/MediaObjects/296_2013_2915_Fig2_HTML.gif
Fig. 2

Overall prevalence (a) and incidence (b) of SLE in various countries

The incidence (per 100,000) is over 5 in the USA [9, 11, 12, 21] and 3–5 in Europe [14, 30, 31, 33, 34, 38] and Asian countries [2729]. Our result was comparable to that reported for Hong Kong and Taiwan. The incidence in the present study was about ninefold higher in females than in males, and in other studies approximately fivefold to eightfold higher [14, 28, 29, 34, 37, 38]. Similar to Taiwan [28], the incidence of SLE increased continuously with age until its peak, and then declined slowly thereafter (as did the prevalence). However, the incidence for female Norwegians exhibited a bimodal pattern, with first and second peaks occurring at 16–29 and 50–59 years, respectively. This pattern might be related to the use of contraceptive pills during the reproductive age or to the use of hormone therapy after menopause [14]. In other European countries, including the UK, Spain, and Denmark, the incidence of SLE increases until the age of 20–39 years and remains high thereafter to the age of 50–69 years, although there are some differences in the age at which this peaks [30, 34, 35]. In the USA, the incidence of SLE appears to grow steadily with age [11, 12, 21]. In the Caucasian population, late-onset SLE is reported to be more prevalent [42] and the clinical course is considered to be more benign compared to SLE onset earlier in life [39]. In addition, SLE in Asians is known to be more severe and to have a greater mortality rate [15]. These findings may explain why the peak age in both Europe and the USA appears to be higher and the incidence remains high in older age group.

It is difficult to conclude that SLE is more or less frequent in some countries than in others, because differences of SLE burden between countries might be due to the differences in the study population, design, data source, study period, diagnosis, and diagnostic criteria. However, regional disparities appear to hold true. Differences across countries might be mainly explained by differences of racial makeup in countries. This can be inferred from studies in which differences between ethnic groups who live in the same region were compared: SLE was not only more predominant but also more severe among African Americans, Asians, Native Americans, and Hispanics than among Caucasians [14, 15, 39]. However, even taking into consideration the racial composition, the prevalence of SLE among Asians who live in Europe [14, 15] or the USA [11, 13] appears to be higher than those who reside in their homeland. These findings might also reflect differences in healthcare environmental factors across countries, including the healthcare system, accessibility to medical care, case-finding techniques, and therapeutic environments, together with other risk factors such as industrial pollution and exposure to sunlight [40, 41].

In the present study, we observed a slightly increasing trend in prevalence and incidence. Changes in the incidence and prevalence of SLE have been reported in several studies. The studies concerning trends in the incidence over several decades [9, 37] reported significant increase trends, but other studies, which were recently conducted during relatively short period, have showed almost constant trends [14, 35]. Our increasing trend might be explained by raising social awareness on the disease and expanding coverage of copayment beneficiaries program for rare disease.

Previous studies on SLE have been conducted using medical records from either single centers or specific regions. Even though the use of medical records has an advantage that SLE could be confirmed by ACR classification criteria [1, 14], it has a difficulty to generalize the findings of those studies. Moreover, in case of rare diseases, it is not easy to conduct a nationwide-scale study. For such reasons, health insurance claims data are widely used for researchers. However, there remain some issues that require attention. Even though the Korean NHIC has made an effort to reduce inaccuracies, the diagnostic information in the data is often inaccurate, either due to simple coding errors, misclassification due to a lack of medical knowledge, or the reimbursement system itself [43, 44]. Therefore, cases with a specific disease need to be identified based on a disease-specific algorithm, not simply a diagnostic code. A study from Canada defined the subjects as being patients with SLE based on the presence of ≥1 billing code by a rheumatologist, ≥2 billing codes (≥8 weeks apart but within 2 years) by any physician, or one hospitalization diagnosis [22]. Another study from the USA defined subjects as SLE prevalent if they had at least one inpatient claim with an SLE diagnosis or ≥2 office or emergency room visits at least 30 days apart, within the 12 months following the earliest date of service of a medical claim, with a diagnosis of SLE [12]. These components and their combination may differ between countries. The present study developed several algorithms using information on hospitalization due to SLE, prescription of immunosuppressants, steroids, and hydroxychloroquine, and laboratory examination of anti-dsDNA antibody and complement (C3 or C4). The identification of patients using such algorithms will help when using claims data collected before the beginning of the ICBP for studies on various topics such as healthcare utilization, patterns of care, medical costs, and disease incidence and prevalence.

The present study was subject to several limitations. First, the administrative claims data that were analyzed were obtained only as a result of subjects visiting healthcare institutions. No information was therefore available for SLE patients who did not visit a healthcare institution. That could influence underestimation of the SLE burden. However, it might have had little impact on the findings since NHI claims data cover almost all Koreans and the expanded coverage of the NHI system has made it easy for people to access health institutions. The second limitation relates to the definition of SLE prevalent and incident cases. While SLE patients may have long periods of remission, 2.3 years on average (range 1.0–5.7 years) [45], all of our algorithm-identified SLE cases were patients who either received treatment such as hospitalization and medications or had SLE-related laboratory examinations each year. Therefore, if their disease activity was in remission and they did not require treatment or undergo any of the aforementioned examinations, they were not regarded as SLE patients in the present study. This might have led to an underestimation of the SLE prevalence. Conversely, the incidence might have been overestimated because we defined SLE cases as incident only if prevalent cases had not had SLE for the preceding 2 years and had SLE for 2 years consecutively thereafter.

In summary, the nationwide prevalence and incidence of SLE in South Korea were estimated using NHI claims data that covered almost all Koreans. The prevalence (per 100,000) of SLE in Korea increased from 20.6 in 2006 to 26.5 in 2010, and the incidence (per 100,000) was about 2.5. Estimating the nationwide burden of disease is an important first step toward understanding the public health impact of this disease. The algorithm selected to identify SLE cases may facilitate various studies that employ claims data.

Acknowledgments

This study was supported in part by grants from the Korea Healthcare Technology R&D Project, Ministry of Health and Welfare, Republic of Korea (A080588 and A120404).

Conflict of interest

None.

Supplementary material

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