Our study demonstrated a documented increase in the incidence of urolithiasis from 1995 to 2016 in the Wuwei area, consistent with the epidemic trend of urinary calculi worldwide 15–18. The increasing trend in urolithiasis morbidity in Wuwei can be divided into intrinsic and extrinsic factors. The former includes age, sex, and familial background; while the latter includes climate, environment 19, lifestyle, dietary habits 20, and regional and socioeconomic conditions 21. The increase in the incidence of urinary calculi has exacerbated the burden on medical systems 5 22. Furthermore, with improvement in medical insurance, many more people have the opportunity to seek medical care, which has had an impact on the statistical incidence of urinary calculi.
Our results demonstrated that the incidence of urinary calculi was higher in males than in females, with a sex ratio of 2.32:1. Previous studies have shown that the proportion of males to females with urolithiasis is 1.7–3.0:1 23 24. Many factors may accelerate the incidence of urolithiasis in males, such as higher BMI 25 (BMI > 30 is positively correlated with urolithiasis) and testosterone 26. Our study showed that people aged 30–59 years (62.32%) had a higher incidence of urinary calculi, similar to results reported in the United States, Germany, Iceland, and Iran 27 28. The reason why middle-aged populations may be more prone to urolithiasis could be due to lower fluid intake and higher rates of dehydration when performing laborious work 29 as well as unhealthier lifestyles and occupational stress 30. In the current study, 49.5% of patients were farmers, and significant diversities in occupation were identified by region (P < 0.001). From 1995 to 2016, the overall proportion of workers increased, which may be explained by increased urbanization and industrialization in recent years 31. In addition, 86.7% (4 616/5 497) of patients with urinary calculi may be under both family and society pressure and may relieve stress via poor habits such as smoking and drinking 32, resulting in an increase in the number of patients with urinary calculi in married people. Therefore, regulating stress and changing poor habits could help reduce the probability of developing stones32.
In our cohort, both sexes show an upward trend in the incidence of urolithiasis, but the trend was more pronounced for women 24. On average, the incidence of standardized urolithiasis was 19.41% higher per year in females than in males, although Joinpoint regression was unchanged from 1995 to 2016. Furthermore, the change in APC of urolithiasis incidence in females during this period was statistically significant. Based on nationwide hospitalized patients between 1997 and 2002, the overall incidence of urolithiasis in males and females dropped from 1.7 to 1.3 10. This change may result from a variety of etiologies, such as obesity, which is related to an increased risk of urinary calculi and is more common in females than in males 33. In addition, stone formation and dietary components exhibit a strong relationship, with high rates of obesity and animal protein intake considered risk factors in westerners 33. These risk factors are becoming increasingly common among Chinese women 4. Women can also experience greater occupational stress than men 29, with changes in home-work dynamics also increasing pressure on women.
Based on the distribution of urolithiasis in different areas, our study demonstrated that the annual incidence was highest in Hongshagang, a northwestern desert region in Wuwei, which has frequent water shortages and water with high mineral content. Notably, studies have identified a strong association between drinking water quality and the incidence of urinary calculi 34 35. For example, Stoots and colleagues studied mineral content in drinking water and found that water intake is critical for stone prevention and mineral content in water can affect stone formation, bone health, and cardiovascular (CVD) risk 35. From 1995 to 2016, the incidence of urinary calculi in Wuwei showed a fluctuating but growing trend. As seen in Fig. 5, the prevalence of urolithiasis was generally low before 2009, with only a few regions showing a high incidence. Most regions located south of Wuwei, e.g., Tianzhu, differed from other towns regarding geographical location, dietary structure, and local lifestyle. Tianzhu is a Tibetan autonomous county, with a large population of Tibetan residents, who consume greater quantities of beef and mutton offal, butter tea, animal fat, and other high cholesterol foods 36. Furthermore, long-term grazing work and irregular diets are closely related to the occurrence of urolithiasis. At the same time, local drinking water, which comes from snow melt and groundwater, contains higher levels of trace elements, bacteria, and parasites, which may induce stone formation through long-term consumption 37. Here, based on spatial trend analysis, the distribution of urolithiasis incidence in various townships was related to geographical location, dietary structure, lifestyle, drinking water, and sanitation.
Our SaTScan results identified four spatiotemporal clusters of urolithiasis incidence in Wuwei, which were non-random and spatially aggregated. Spatial scanning, spatial distribution, temporal clustering, and temporal trend analysis showed consistent results. Based on these results, attention should be paid to those areas with higher rates of urolithiasis, such as Hongshagang township in Liangzhou. In addition to the harsh environmental conditions (e.g., high elevation, arid climate, low precipitation, long days) and poor diets in areas of western China, which differ from conditions in lower latitude areas such as Tianzhu County 38, the gradual declines in urbanization, population migration, and residential population density in areas of Minqin have led to an inadequate urban structure and limited medical resources. Given the high and clustered incidence of urolithiasis in certain areas, e.g., Nanhu and Gulang, residents should be encouraged to limit their intake of risky foods and increase their consumption of healthy foods, especially fresh fruit and vegetables, and to avoid drinking water with high levels of organic pollutants. At risk regions should also adopt local control measures and consider other environmental and social risk factors (e.g., water filters, smoking, drinking to strengthen regional prevention and treatment of urinary calculi 39. Local education and awareness regarding health care and timely medical treatment should also be improved.
Our results showed that the most common medical financing method among patients (70%) was basic social medical insurance, including the NRCMS and basic medical insurance for urban residents and employees. A total of 12% of patients were self-funded, and only 0.2% of patients purchased commercial insurance. In China, rural residents tend to have lower incomes, poorer access to health care, and less medical knowledge than their urban counterparts 10. Among the study counties, Liangzhou has the strongest economic development, with higher employment and therefore better work injury and other insurance. In contrast, the Minqin area lags in all aspects, which is likely due to its reliance on agriculture and animal husbandry, resulting in significantly slower economic development. However, with the overall development of the Chinese economy, basic social medical insurance has gradually improved 40. For example, China established the basic medical insurance system for urban employees in 1998 and implemented the NRCMS in 2003. From 1995 to 2016, the payment method for patients with urinary calculi in Wuwei was primarily under NRCMS, based on the characteristics of its largely rural population structure. With the implementation of NRCMS in 2003 and later improvement in its financing, NRCMS expenditure has shown rapid growth in recent years. The number of people benefitting from NRCMS compensation has increased significantly, especially in Minqin. In this study, the consistent increasing trend in the incidence of urinary calculi between 1995 and 2016 coincided with the change in the NRCMS. In January 2016, the State Council integrated the basic medical insurance system for urban residents and the NRCMS, establishing a unified basic medical insurance system and secure treatment for urban and rural residents 41. Further increases in reimbursement are planned to accommodate the large rural population, which should reduce the medical and economic burden on patients to some extent.
There are several limitations in our research. Firstly, a long-term retrospective study design was used, and the existing research data were relatively limited. Certain data, especially from the early stage of clinical record collection, may be missing, which could impact analysis of some influencing factors. Secondly, due to the diagnosis and characteristics of urinary calculi, treatment can be carried out in a variety of ways. In the early days, patients admitted to hospital were not in the majority. Therefore, the factors analyzed and results discussed may differ from real situations. In our follow-up studies, we will explore those variables not examined in this study. Thirdly, the morbidity data were obtained from the medical records of 12 hospitals in Wuwei from 1995 to 2016, which may limit demographic representation. In the future, research will be expanded to more provinces (and even country-wide) to explore the temporal trends and regional distributions of urinary calculi.