Study population
296,770 of people (17.3% were children aged under 12 years) in 244 villages were examined in Bin County in 2018. The gender ratio of the investigated population was 1.12:1 (male to female). Overall, 1.34% were reported suffering from KBD, with no new cases discovered in children. The age of the patients ranged from 19 to 97 years old. Amongst patients with KBD, 52.9% were males and 47.1% were females. Patients with KBD of grade I, II and III accounted for 57.4%, 37.4% and 5.3% of the total amount, respectively. 44.6% of them had been taking medical treatment for a long-term. Farmers were the main occupation for KBD patients. 39.9% never received education, and 19.2% were from poor poverty-stricken households whose annual net income per capita was lower than 2950 RMB.
Age-sex distribution of YLDs for KBD
Table 1 showed the calculated YLDs in different KBD grades by gender. The total health loss from KBD in Bin County in 2018 was estimated at 858.78 YLDs (2.89 YLD per 1000 population, 53.8% for males and 46.2% for females). YLDs for males were higher in all grades of KBD than those for females, but with no statistical significance (p > 0.05). Among different KBD grades, KBD of grade II contributed most to the YLDs, followed by KBD of grade I, accounting for 54.4% and 31.0% of the total YLDs respectively. The same trends were observed for males and females. When compared with the prevalence rate of KBD, it was found that there was no consistent corresponding relationship. Although the largest contribution of YLDs was KBD of grade II (1.58 YLD per 1000 population), the highest prevalence rate was observed in KBD of grade I (0.77%).
Table 1
Years lived with disability (YLDs) for KBD in Bin County (2018)
KBD grades
|
Male
|
Female
|
Total
|
Prevalence
(%)
|
YLDs
|
YLDs
|
YLDs
|
YLD/1000
|
I
|
136.42
|
129.87
|
266.29
|
0.90
|
0.77
|
II
|
258.99
|
208.59
|
467.58
|
1.58
|
0.50
|
III
|
66.82
|
58.10
|
124.92
|
0.42
|
0.07
|
Total
|
462.23
|
396.56
|
858.78
|
2.89
|
1.34
|
Figure 2 displayed the age-specific distribution of YLDs between genders and KBD grades in Bin County. According to the distribution of the number of patients, age was divided into five groups: 19~, 40~, 50~, 60~, 70 years and over. The age group of 0 ~ 18 was not included in Fig. 2 as there were no cases under the age of 18 years. The results showed that YLDs increased with age and decreased at the highest 50 ~ age group (330.49 YLDs, 38.5% of total YLDs). Approximately 85.6% of the total YLDs were from the age group of 50 years and above. YLDs in KBD of grade II were the highest in all age groups, followed by KBD of grade I. There were no significant differences in YLDs among KBD grades (p > 0.05). These trends were generally consistent in the two genders, only with relatively high YLDs for males in all age groups.
Spatial distribution of health loss from KBD
Figure 3 presented the spatial distribution of healthy life years loss from KBD in Bin County at the village-scale. Obvious regional variations were observed in both YLDs and YLD rate, with higher values in the southern regions and lower values in the northern regions of Bin County. Areas with the most serious health loss were mainly clustered in the southwest. The loss of healthy life years from KBD in villages of Bin County ranged from 0 to 25.50 YLDs, while their YLD rates had a larger variation, ranging from 0 to 40.47 YLD/1000. The top five townships with the highest YLD rates were Hanjia (19.83 YLD/1000, 97.16 YLDs), Xiangmiao (6.04 YLD/1000, 78.49 YLDs), Tandian (5.74 YLD/1000, 88.97 YLDs), Xinbaozi (5.54 YLD/1000, 73.43 YLDs), and Chejiazhuang (4.95 YLD/1000, 69.39 YLDs).
Spatial autocorrelation and hotspot detection
To detect the spatial autocorrelations of YLDs and YLD rate, global Moran’s I statistics were calculated at village-level in Bin County. It was found that the Moran’s I index values for YLDs and YLD rate were 0.27 and 0.37, indicating that the distribution of health loss from KBD have positive correlations. The Z score, which is a standardized statistic, for YLDs and YLD rate were 7.607 (p < 0.0001) and 10.511 (p < 0.0001), respectively. Apparently, the global spatial autocorrelations of YLDs and YLD rate presented significant spatial clustering. Villages with KBD cases were not randomly distributed in space among all villages in Bin County. Similarly, the YLDs and YLD rate of different gender groups also showed significant spatial clustering at village-level. The Moran’s I index values of YLDs and YLD/1000 for males were 0.15 and 0.21 (p < 0.01), those for females were 0.12 and 0.17 (p < 0.01), respectively.
To further identify the locations of significant clusters (hot and cold spots), Anselin local Moran’s I index was applied at village-level in Bin County. Maps in Fig. 4 showed the locations with significant local Moran’s I statistics and classified those locations by type of association (LISA cluster map). The high-high and low-low clusters are indications of high values surrounded by high values and low values surrounded by low values. In contrast, the high-low and low-high locations are indications of spatial outliers. There were some outstanding spatial clusters of both YLDs and YLD/1000 observed in Bin County. The clustered villages with high YLDs and YLD/1000 (hotspots) were found to cover most areas of Hanjia and Chejiazhuang Townships in the southwest and parts of Tandian and Xiangmiao Townships in the east of Bin County. The clustered villages with low YLDs and YLD/1000 (cold spots) were mainly found in the north and central of Bin County, covering Xipo, Yongle, Xinmin, Xiaozhang and Chengguan Townships. The hotspots of YLDs were slightly different from that of YLD/1000. Several clustered villages with high YLDs were also observed in Xinbaozi and Longgao Townships, discontinuously distributed in the southeast of Bin County.
Effect of environmental factors on health loss
We computed Spearman’s correlation coefficients and its 95% confidence intervals to assess the relationships between the health loss and variables of interest (Table 2). Natural factors related to environmental Se contents and social factors including the poverty rate and educational attainment were selected for the correlation analysis. The results showed that YLDs and YLD rate of KBD had no significant correlations with the total Se contents in soil and wheat, but were positively and significantly correlated with organically bound Se in soil (rYLDs = 0.216, rYLD/1000 = 0.217, p < 0.05, N = 83). By contrast, the prevalence of KBD had no significant correlations with any environmental Se factors. As for social environmental factors, only the poverty rate of patients with KBD showed significantly positive correlations with YLD rate (r = 0.267, p < 0.05, N = 83) and prevalence rate (r = 0.264, p < 0.05, N = 83).
Table 2
Spearman’s correlation coefficients for YLDs, YLD rate, prevalence and environmental factors
|
Natural environmental factors
|
Socio-economic factors
|
|
Soil Se
|
Wheat Se
|
Available Sea
|
Organic Se
|
Poverty
|
Education
|
YLDs
|
0.153
|
-0.008
|
-0.052
|
0.216*
|
0.203
|
0.223
|
YLD/1000
|
0.150
|
0.064
|
-0.070
|
0.217*
|
0.267*
|
0.220
|
Prevalence
|
0.140
|
0.089
|
-0.060
|
0.213
|
0.264*
|
0.213
|
a Available Se represents water-soluble and exchangeable fractions of Se in soil. |
* indicates significant (p < 0.05). |