| Background Systemic lupus erythematosus (SLE) is an common autoimmune disorder. Recently, SLE has become another major threat for women health in China besides breast cancer. It has become an important public health issue in China. In the past few decades, many large-scale epidemiological studies of SLE were conducted in the United States and Europe. Meanwhile, many scholars also have conducted a number of epidemiological studies of SLE in China. However, results of these studies could not represent the natural population, and there was still lack of truly large-scale epidemiological studies of SLE in China. The etiology and pathogenesis SLE is complex, and is not yet clarified untill now. It is generally accepted that SLE is multifactorial and caused by an interaction of genetic, environmental, behavioral, and psychosocial factors. Currently, many studies are keen to look for susceptibility genes of SLE, but the heritability of SLE was only 40%-60%, and environmental factors must play an important role in the pathogenesis of SLE. Though ultraviolet exposure and some drugs have been clearly considered a predisposing factor for the SLE pathogenesis, the association of other environmental factors with SLE is still needed to be explored in the future study.ObjectivesThe aims of the present study were to explore the prevalence of SLE in Anhui's rural population based on a large-scale epidemiological study, find the related environmental factors of SLE, and provide the understanding for the prevalence of SLE, clarifying the cause and pathogenesis of SLE, as well as establishing effective prevention measures.MethodsFrom September 2008 to March 2011, a large-scale epidemiological study of SLE was conducted in many regions of Anhui province. The current study consists of two parts: in the first part, we obtained the prevalence of SLE in Anhui's rural population by cross-sectional study. We identified the study site by two-phrases sampling. In the first phase, we randomly selected a county-level city, two districts, and eight counties in Anhui province. Then we randomly selected 15% of administrative villages in these regions as the study site. An epidemiological study was conducted to explore the prevalence of SLE in these administrative villages. Patients with SLE were determined by two-phrases screening. In the first phase, investigators shepherded by village doctors screened SLE patients by household survey. In the second phase, clinical rheumatology experts futher confirmed these patients in the local public health center. Meanwhile, we collected the information of the resident population to calculate the prevalence of SLE, and obtained the gender distribution, age distribution, and regional distribution of SLE prevalence. In the second part, we obtained environmental factors related to the pathogenesis of SLE by case-control study. 260 SLE patients were collected in the case-control study. Meanwhile, 260 normal controls were recruited. All patients were fulfilled with the 1997 American College of Rheumatology classification criteria for SLE (ACR). The controls were considered to be healthy individual without autoimmune diseases. Information of environmental factors were collected by unified questionnaires, which include demographic characteristics, menstruation and fertility, lifestyle and personal habits, living environment, psychosocial factors, et al. Logistic regression were used to analysis the effect of environmental factors and the interaction between factors on the risk of the SLE. Results(1) We randomly selected 439 administrative villages including 1,253,832 resident population. 471 SLE patients (41 males, 430 females) were identified using the criteria set for the diagnosis of SLE by 1997 the American College Rheumatology (ACR). The crude prevalence was estimated to be 37.56 per 100,000 population (95%CI: 34.17~40.96) in Anhui's rural population. The resident population was selected as the standard population distribution of Anhui fifth census in 2000, and the standardized prevalence was 36.03 per 100,000 population (95%CI: 35.54~36.51) in Anhui's rural population.(2) There was gender difference in prevalence of SLE (χ~2=340.64,P<0.0001). The crude prevalence of SLE was 6.39 per 100,000 population (95%CI: 4.43~8.34) in males. The crude prevalence of SLE was 70.28 per 100,000 population (95%CI: 63.64~76.93) in females. The standardized prevalence was 6.17 per 100,000 population (95%CI: 5.89~6.45) in males. The standardized prevalence was 67.78 per 100,1000 population (95%CI: 66.83~68.73) in females. The ratio of males versus females was about 1:11.(3) There was age difference in prevalence of SLE (χ~2=261.05,P<0.0001). The peak prevalence was 40 to 50 years old. The prevalence of SLE was 88.66 per 100,000 population (95%CI: 74.13~103.18) in this age group. The lowest prevalence was 0 to 10 years old. The prevalence of SLE was 1.82 per 100,000 population (95%CI: 0~3.89) in this age group. The peak prevalence in males was 40 to 50 years old. There was 9 SLE patients in this age group, accounting for 21.95% of male patients. The prevalence of SLE was 10.70 per 100,000 population (95%CI: 3.71~17.70) in this age group. The peak prevalence in females was also 40 to 50 years old. There was 134 SLE patients in this age group, accounting for 31.63% of female patients. The prevalence of SLE was 173.54 per 100,000 population (95%CI: 144.18~202.90) in this age group.(4) There was regional difference in prevalence of SLE, but not significantly (χ~2=2.32,P=0.314). The prevalence in northern region of Anhui is higher than the prevalence in central region of Anhui, and the prevalence in central region of Anhui is higher than the prevalence in southern region of Anhui. The prevalence in northern region was 40.49 per 100,000 population (95%CI: 34.92~46.05). In central region of Anhui, the prevalence of SLE was 36.68 per 100,000 population (95%CI: 31.31~42.05). The prevalence in southern region of Anhui was 33.66 per 100,000 population (95%CI: 26.67~40.65).(5) Results from univariate logistic regression analysis showed that the following factors were significantly associated with the pathogenesis of SLE: birth (OR=16.970, 95%CI=5.193~55.454, P<0.0001), menstruation (OR=2.131, 95%CI=1.285~3.536, P=0.003), age of menarche (OR=0.724, 95%CI=0.640~0.818, P<0.0001), age of first childbirth (OR=1.378, 95%CI=1.247~1.521, P<0.0001), smoking (OR=3.756, 95%CI=1.871~7.540, P=0.0002), drinking (OR=2.676, 95%CI=1.477~4.848, P=0.001), delicious desserts (OR=3.906, 95%CI=2.651~5.754, P<0.0001), cooking oil (compared to half of each vegetable oil and animal oil, animal oil: OR=2.117, 95%CI=1.092~4.104, P=0.026), taste (compared to medium taste, light taste: OR=2.433, 95%CI=1.580~3.749, P<0.0001), carnivorous (compared to half of each lean and fat, lean: OR=1.477, 95%CI=1.020~2.138, P=0.039, fat: OR=2.883, 95%CI=1.516~5.481, P=0.001), fruit (OR=0.503, 95%CI=0.354~0.713, P=0.0001), spicy food (OR=1.510, 95%CI=1.001~2.277, P=0.049), mushrooms (OR=2.946, 95%CI=2.020~4.298, P<0.0001), hot food (OR=5.314, 95%CI=2.167~13.029, P=0.0003), ultraviolet (OR=2.249, 95%CI=1.553~3.258, P<0.0001), quality of sleep (OR=3.775, 95%CI=2.152~6.621, P<0.0001), manual labor (OR=2.764, 95%CI=1.934~3.950, P<0.0001), housing type (compared to brick houses, adobe houses: OR=3.220, 95%CI=1.232~8.411, P=0.017), drinking water (OR=3.634, 95%CI=2.448~5.395, P<0.0001), noise source (OR=3.638, 95%CI=1.808~7.318, P=0.0003), residence (compared to suburbs, plain: OR=0.519, 95%CI=0.322~0.839, P=0.007), tension (OR=6.763, 95%CI=2.974~15.380, P<0.0001), negative life events (OR=5.182, 95%CI=3.144~8.540, P<0.0001), character (OR=2.511, 95%CI=1.437~4.386, P=0.001), religion (OR=2.527, 95%CI=1.030~6.200, P=0.042), help in emergency situation (OR=0.667, 95%CI=0.457~0.937, P=0.035), and hepatitis B vaccine (OR=1.951, 95%CI=1.345~2.823, P=0.0004).(6) Results of multi-logistic analysis showed that the following factors were siginificantly associated with SLE: birth (OR=4.810, 95%CI=1.260~18.358, P=0.021), delicious desserts (OR=2.459, 95%CI=1.480~4.086, P=0.0005), cooking oil (compared to half of each vegetable oil and animal oil, vegetable oil: OR=0.574, 95%CI=0.338~0.975, P=0.040), taste (compared to medium taste, salty taste: OR=1.425, 95%CI=0.805~2.524, P=0.015), carnivorous (compared to half of each lean and fat, lean: OR=1.906, 95%CI=1.130~3.216, P=0.015, fat: OR=2.433, 95%CI=1.033~5.731, P=0.041), ultraviolet (OR=1.711, 95%CI=1.008~2.904, P=0.046), quality of sleep (OR=2.804, 95%CI=1.383~5.686, P=0.004), manual labor (OR=2.930, 95%CI=1.578~5.439, P=0.0007), drinking water (OR=3.255, 95%CI=1.819~5.824, P<0.0001), residence (compared to suburbs, plain: OR=0.458, 95%CI=0.237~0.884, P=0.019), negative life events (OR=2.305, 95%CI=1.198~4.435, P=0.012), hepatitis B vaccine (OR=3.058, 95%CI=1.728~5.411, P=0.0001), menstruation (OR=2.422, 95%CI=1.165~5.037, P=0.017), age of menarche (OR=0.714, 95%CI=0.596~0.856, P=0.0003), and age of first childbirth (OR=1.193, 95%CI=1.049~1.335, P=0.007).(7) Interaction between environmental factors were carnivorous and lack of manual labor (OR=81.288, 95%CI=1.600~4129.204, P=0.028), drinking water and ultraviolet (OR=5.355, 95%CI=1.512~18.957, P=0.009).ConclusionsThis study suggests that the prevalence of SLE in Anhui's rural population is 37.56 per 100,000 population, and the standardized prevalence is 36.03 per 100,000 population. There were sex, age, and regional differences in prevalence of SLE in Anhui's rural population. Many environmental factors, including birth, delicious desserts, cooking oil, taste, carnivorous, ultraviolet, quality of sleep, manual labor, drinking water, residence, negative life events, hepatitis B vaccine, menstruation, age of menarche, and age of first childbirth may be related to SLE risk in Anhui's rural population.
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