Abstract
The aim of this study was to determine the prevalence and incidence of Systemic Lupus Erythematosus (SLE) in Tucumán, Argentina. Methods: The study included inpatient and outpatient charts from four public hospitals and private practice rheumatology clinics, all of them members of the Tucumán Rheumatology Society. Patients older than 16 years with diagnosis of SLE between January 2005 and December 2012 were included. Prevalence and annual incidence were calculated as the number of cases per 100.000 inhabitants during the period 2005 to 2012. Results: Three hundred fifty-three patients were identified. The mean age at diagnosis was 30.5 ± 11.7 years, 93.5% women, 83% mestizos. Prevalence was 24.3 cases/100.000 inhabitants (CI 95% 22.6–28.8) and age-adjusted (≥16 years) of 34.9 cases/100.000 inhabitants (CI 95% 32.8–41.1). The annual incidence in 2005 was 1.8 cases/100.000 inhabitants (95% CI 1–2.9) and 2012 of 4.2 cases/100.000 inhabitants (95% CI 2.9–5.8). Mortality was 9.1%, with infections being the most frequent cause (14/32). Conclusion: The prevalence of SLE in the province of Tucumán was 34.9 cases/100.000 inhabitants.
Key messages
Incidence and prevalence rates of lupus in Tucumán were similar as previously reported in other countries. Incidence rate peak was on the 20s for both sexes. Most frequent cause of mortality was infections.
Introduction
Systemic Lupus Erythematosus (SLE) is a multi-systemic autoimmune disease with a complex and diverse nature in its clinical presentation. It occurs more frequently in young, fertile women and can appear in all ethnicities. 1
Prevalence and incidence of SLE show considerable variation in different regions, and between ethnic groups within a region. 2
Literature from the northern hemisphere has shown that socioeconomic factors and ethnicity have a major impact on the incidence, disease activity, damage and mortality of this disease. One of the principal findings has been that non-Caucasian patients develop SLE more frequently and experience major organ involvement (renal, heart, lung and central nervous system) leading to diminished survival when compared to Caucasians.3–14 Non-Caucasian patients tend to be younger at disease onset; they also present more damage accrual. Increased mortality rates in non-Caucasian SLE patients seem to be primarily related to socioeconomic status (SES) factors. 15
In a paper published by Scolnik et al., 16 incidence and prevalence of SLE rates of a health management organization in Buenos Aires, Argentina, were similar to those reported in other studies in Latin and North America.
Tucumán is a province situated in the north of Argentina and divided into17 departments with a population of 1.448.188 inhabitants. Forty five percent of its population lives in the center and the remaining 65% in the east, west and south. 17 In the current study, we examined the prevalence and described the annual incidence over a time period of adult SLE patients in this region of Argentina.
Patients and methods
Tucumán is an important province from the northwest region of Argentina, located about 1100 kilometers from Buenos Aires. Population figures in Tucumán according to year and age were retrieved from 2010 National Census. 17 The total adult population (over 16 years) was 1.011.188 people, distributed in: Center area 507.016, Western area 11.891, Eastern area 183.296 and Southern area 201.985.
Population and healthcare: The population of Argentina is the result of ethnic intermixing between several groups, including Indigenous American, European and African populations. Despite the common idea that the population in Argentina is of mostly European origin, multiple studies have shown that this process of admixture has had an impact on the entire population. 18
Argentina, including Tucumán, has a health system divided into three large sectors - public, social security, and private - as found in many Latin American countries. All public hospitals and primary care centers are run by the provincial government.
All Tucumán citizens and residents, including foreign workers or tourists, can get medical care, free-of-charge in the province. In addition, the public hospitals are sometimes also used by insured individuals requiring more complex and expensive diagnostic or therapeutic procedures.
The social security sector is the dominant health subsector in Argentina. The Obras Sociales Nacionales (OSNs), mostly managed by trade unions, care for workers within the same labor activity and their core family members. The social insurance sector provides health coverage to 60% of the population, including Tucumán.
The private insurance sector covers approximately 5% of the population.
The distribution of health personnel (rheumatologists) is uniform in all areas of the province (Figure 1).
Distribution of health care by areas.
For the purpose of our report, we included inpatients and outpatients from four public hospitals in the province, and private practice cared for by rheumatologist, all of them members of the Tucuman Rheumatology Society (n 28).
We received data collection sheets containing inpatients’ and outpatients’ information from 1 January 2005 to December 2012.
Only adult patients living in Tucumán were included.
Researchers evaluated and reached consensus on SLE diagnosis based on the updated American College of Rheumatology (ACR 1982/97) classification criteria,19,20 and only patients fulfilling four or more criteria were included in the study. The study was approved by the Hospital´s Ethics Committee.
We considered age at the first ACR criterion fulfilled, age at diagnosis, ethnicity, clinical manifestations, death, and cause of death.
Ethnicity was defined according to GLADEL criteria; 21 Caucasians: patients with four European ancestors, Amerindian: four American Indian ancestors, Mestizos: patients with mixed Amerindian and European ancestors and Afro-latinamericans: patients with at least one African ancestor.
Statistical analysis: Period prevalence rates were calculated using all patients with definite SLE observed during the period between January 1, 2005 – December 31, 2012, whereas incidence rates were calculated using only true incident cases, that is, those diagnosed during the one-year study period. Incidence and prevalence rates were calculated as the number of cases per 100.000 inhabitants. Ninety-five percent confidence intervals (CIs) for rates were calculated. Survival rates were estimated using the Kaplan–Meier method.
Results
A total of 395 cases of SLE among residents of the study area were evaluated for this study, 42 were excluded for being diagnosed before the age of 16 or for not fulfilling 4 SLE criteria after evaluation. Finally, 353 patients were included.
The mean age at diagnosis was 30.5 ± 11.7 years, 93.5% were women and 83% mestizos. Arthritis and cutaneous involvement were the most frequent clinical manifestations.
The calculated prevalence of SLE was 34.9 cases/100.000 inhabitants (95% CI 32.8–41.1), with a female:male ratio of 14.3:1.
The higher prevalence was seen in the center area (urban) with 38.5/100.000 inhabitants, followed by west 37.8/100.000 inhabitants, east 31.1/100.000 inhabitants and south 23.3/100.000 inhabitants.
Annual incidence in our study was 1.8/100.000 inhabitants (2005) and 4.2/100.000 inhabitants (2012) being particularly high in the last year (Table 1). The peak incidence rates were seen in the 20–29 age group for both sexes (Figure 2).
Annual incidence of SLE in Tucumán, Argentina.
CI: confidence intervals.
Age at systemic lupus erythematosus (SLE) diagnosis.
A total of 32 deaths were identified among the 353 SLE patients during the study period. Mortality was 9.1% (95% CI 6.28–12.55) and the most common cause was infections (43.75%). The 5 and 10 year survival rates were 96% and 93%, respectively.
Discussion
SLE is an autoimmune disease, and its prevalence varies in different countries. These differences are partially explained by ethnic and environmental factors involved in the pathogenesis of the disease and the different methods of recruitment.
The prevalence found in Tucumán was 34.9 cases/100.000 inhabitants considering the population over 16 years.
Epidemiologic studies on Systemic lupus erythematosus (SLE) are scarce in Latin America and have reported annual incidence rates of diagnosed SLE between 4.7 to 8.7/per/100.000 person-years, and prevalence ranged from 47.6 to 90 per 100.000 habitants. 22 In another Argentinean study, 16 prevalence of lupus was 58.6/100.000 inhabitants assessed in a health management organization in Buenos Aires.
Around the world, incidence rates of SLE range from approximately 1 to 10 per 100.000 person-years and prevalence rates generally range from 20 to 70 per 100.000 inhabitants. 22
Our results differ from some countries such as Italy, 23 where prevalence described by Govoni in 2006 was 57.9, similar to Spain with 34.1 cases/100.000 inhabitants. 24
The annual incidence in our study was 1.8 (2005) and 4.2 (2012), a marked increase in the last year. The increase in the annual incidence is difficult to explain. It may be that this increase may have been due to better access to health services, better diagnosis, or increased physician awareness of SLE in recent years and early referral of patients to specialized services. Other studies from European countries like Greece also confirmed an increased incidence in the last two decades. 25
On the other hand, incidence of SLE in other countries like Sweden was notably constant. 26
The peak incidence rates occurred in the group aged 20–29 years, with a mean age at diagnosis of about 30 years, similar as reported in the GLADEL cohort, although data from other epidemiological studies in Europe vary widely.
SLE affects women more frequently than men, with a female to male ratio exceeding 9:1. Hispanic and Asian women also experience SLE at higher rates than white women27,28 as demonstrated in this study with a ratio of 14:1.
The most common symptoms of SLE include skin rash, photosensitivity, oral ulcers, arthritis and fever. 29 In our study population, cutaneous involvement and arthritis were also the most prevalent clinical manifestations.
Mortality in SLE has decreased significantly in recent years. Bellomio et al. evaluated mortality in SLE in Argentina (1990 –1998) with a 5 and 10-year survival of 91% and 85%. 30 In our study survival was 96% and 93% respectively.
In two studies published by the Eurolupus Project Group, with a follow-up of 5 and 10 years, it was shown that infection remains a stable cause of death, comparable to that caused by cardiovascular disease or disease activity. 31 , 32 Mortality was 9.1% in our study and infections were also the most common cause of death.
The main limitations of our study are those inherent to the use of medical charts of subjects that were in control only by rheumatologists. We used different sources for case identification so as to reduce potential underestimation of SLE cases. On the other hand, SLE is a difficult condition for diagnosis due to the spectrum of symptoms and non-specific signs it presents. In this study, the diagnosis was made by rheumatologists, which could decrease the bias. Even so, it is still possible that a small number of SLE patients living in the study area could escape our recording system. However, we think these patients could represent a very small percentage of SLE cases in the area we studied.
Despite all limitations, this study provides relevant data that may allow planning health strategies in the future.
In conclusion, we calculated incidence and prevalence of SLE in a province from the north of Argentina and the results were within the estimates ranges as previously reported in other countries.
Footnotes
Declaration of conflicting interests
The author(s) declared no potential conflicts of interest with respect to the research, authorship, and/or publication of this article.
Funding
The author(s) disclosed receipt of the following financial support for the research, authorship and/or publication of this article: This study was supported by the SARFILINE grant from the Argentine Society of Rheumatology.
Acknowledgements
The authors also gratefully acknowledge Research Unit of the Argentine Society of Rheumatology (UNISAR) for their most helpful comments to this manuscript.
