Study on association factors of intestinal infectious diseases based-Bayesian spatio-temporal model - BMC Infectious ...

Descriptive results

Overall, 32,548,000 IIDs cases were reported in China from 2006 to 2017, and the annual national incidences of IIDs changed from 56.3898/100,000 in 2006 to 93.1011/100,000 in 2019. According to the descriptive summary, HFMD was the most common intestinal infectious disease. The total incidence rates and number of cases of IIDs in China from 2006-2017 (1/100,000) are showed in Table 1.

Table 1 The total incidence rates and number of cases of IIDs in China from 2006-2017 (1/100,000)

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Spatial and temporal distribution of IIDs

Cholera

The national prevalence of cholera fell from 0.012/100,000 in 2006 to 0.001/100,000 in 2017. Most cases were concentrated in coastal provinces, like Zhejiang, Fujian, and Hainan, while in central China, there was a mass of zero cases. During the study period, the highest number of reported cases was 89 in Hainan in 2008. Figure 1 Spatio-temporal distribution of cholera.

Typhoid fever

The national prevalence of typhoid fell from 1.25 cases per 100,000 in 2006 to 0.64 cases per 100,000 in 2017. The spatial distribution of typhoid showed a difference between southern and northern China, in which the morbidity in the south was higher than in the north. Yunnan was the province with the highest typhoid prevalence in China, with 9.66 cases per 100,000 in 2006 and 3.59 cases per 100,000 in 2017. Figure 2 Spatio-temporal distribution of typhoid fever.

Paratyphoid fever

The national prevalence of paratyphoid decreased from 0.74 cases per 100,000 in 2006 to 0.15 cases per 100,000 in 2017, however, the morbidity of several provinces increased in 2016 and 2017, like Yunnan, Guangxi, Guangdong, and Fujian. The occurrence of paratyphoid concentrated in southern China, especially Yunnan, the province with the highest paratyphoid prevalence, with 8.71 cases per 100,000 in 2006 and 4.81 cases per 100,000 in 2017. Figure 3 Spatio-temporal distribution of paratyphoid fever.

Bacillary dysentery

The national prevalence of bacillary dysentery fell from 32.10 cases per 100,000 in 2006 to 7.85 cases per 100,000 in 2017, a clear reduction in occurrence over time as it showed in Fig 4. Spatially, the morbidity in north-western China was higher than in south-eastern provinces. Overall, Beijing and Tianjin were the two provinces with the highest morbidity of bacillary dysentery in China. In 2006, the morbidity in Beijing, 226.82 cases per 100,000, was the highest in China, and in 2017 the highest was Tianjin with 53.66 cases per 100,000 residents. Figure 4 Spatio-temporal distribution of bacillary dysentery.

Amoebic dysentery

The national prevalence of amoebic dysentery decreased from 0.26 cases per 100,000 in 2006 to 0.08 cases per 100,000 in 2017. Spatially, southern China had more cases than northern China, except for Heilongjiang, in which the morbidity reached 2.16 cases per 100,000 was the highest during the study period. Figure 5 Spatio-temporal distribution of amoebic dysentery.

Hepatitis A

The national prevalence of hepatitis A fell from 5.25 cases per 100,000 in 2006 to 1.37 cases per 100,000 in 2017. The preponderance of hepatitis A cases was in north-western China, like Xinjiang, Gansu, and Qinghai. In Xinjiang, the morbidity was 16.52 cases per 100,000 in 2006 and 8.75 cases per 100,000 in 2017, both of which were the highest in China. Figure 6 Spatio-temporal distribution of hepatitis A.

Hepatitis E

Unlike other enteric infectious diseases, the national prevalence of hepatitis E increased from 1.45 cases per 100,000 in 2006 to 2.10 cases per 100,000 in 2017. Hainan witnessed the quickest increase of hepatitis E, while a few provinces like Beijing and Tianjin experienced a decline of hepatitis E. Spatially, eastern provinces had a higher incidence than western and central provinces. The highest morbidity was in Jiangsu, with 4.12 cases per 100,000 in 2006 and 3.48 cases per 100,000 in 2017. Figure 7 Spatio-temporal distribution of hepatitis E.

Hand, Foot, and Mouth Disease (HFMD)

The national prevalence of hand, foot, and mouth disease increased from 1.04 cases per 100,000 in 2006 to 139.84 cases per 100,000 in 2017. Generally, south-eastern China had more cases than north-western China. Figure 8 Spatio-temporal distribution of hand, foot, and mouth disease.

Other infectious intestinal diseases

The national prevalence of OIIDs increased from 56.39 cases per 100,000 in 2006 to 93.10 cases per 100,000 in 2017. The preponderance of other infectious intestinal diseases was in Beijing, Tianjin, and Zhejiang. For the rest provinces, the spatial distribution exhibited evenly in Fig. 9. Figure 9 Spatio-temporal distribution of other infectious intestinal diseases.

Spatial and temporal distribution of covariables

Socioeconomic variables

During the study period, national ARHST increased from 32.30% in 2006 to 62.7% in 2017. Spatially, ARHST in south-eastern China was higher than in north-western provinces. Shanghai owned the highest ARHST while Qinghai had the lowest ARHST. The national GDP increased from 219,028.5 billion yuan in 2016 to 830,945.7 billion yuan in 2017. Spatially, south-eastern provinces had higher GDP than north-western and central provinces. There was an upsurge in national urbanization as well, from 44.34% in 2006 to 60.24% in 2017. Spatially, urbanization in eastern provinces was higher than in western provinces. Figure 10 Spatio-temporal distribution of socioeconomic variables.

Meteorological variables

For meteorological variables, there was no evident temporal change. However, the regional distribution of meteorological variables was uneven. For temperature and precipitation, southern China was higher than northern China. Precipitation in south-eastern and central provinces was higher than in the north-western. There were differences in wind speed between the central provinces and the rest. Figure 11 Spatio-temporal distribution of meteorological variables.

Spatio-temporal evolution of IIDs

Cholera

During the research period, the mean center of cholera remained concentrated in central China, specifically in Anhui, Hubei, and Henan provinces. As for the change in the ellipse representing the distribution, it exhibited various alterations without a predominant trend, suggesting that the spatial distribution of cholera was characterized by fluctuations and no consistent directional pattern was observed. Figure 12 the results of mean center and standard deviational ellipse of cholera.

Typhoid fever

Initially, the mean center of typhoid was situated in Chongqing, after which it gradually shifted southwestward and eventually settled in Hunan province. Correspondingly, the ellipse of typhoid exhibited a similar movement. Initially, it displayed an elongation in the northwest-southeast direction, but over time, it gradually transformed into a more circular shape, signifying a reduction in directional characteristics. Additionally, the minor axes of the ellipse elongated, indicating a more dispersed distribution of typhoid fever. Figure 13 the results of mean center and standard deviational ellipse of typhoid fever.

Paratyphoid fever

The mean center of paratyphoid remained predominantly within Guizhou province, with slight movements towards the northeast, except for the year 2009. Simultaneously, the corresponding ellipse gradually transitioned into a more circular shape and expanded, indicating a broader and more dispersed distribution of paratyphoid. Figure 14 the results of mean center and standard deviational ellipse of paratyphoid fever.

Bacillary dysentery

The mean center of bacillary dysentery remained consistently fixed within Shanxi province, which was reflected in the relatively stable circular shape of the corresponding ellipse. However, the minor axes of the ellipse became shorter over time. Furthermore, the shape of the ellipse exhibited an increasing elongation in the northeast-southwest direction, indicating a more concentrated and intense distribution of bacillary dysentery. Figure 15 the results of mean center and standard deviational ellipse of bacillary dysentery.

Amoebic dysentery

The mean center of amoebic dysentery initially shifted towards the north and subsequently moved towards the south, primarily concentrated within Hubei province. Notably, the corresponding ellipse displayed a clear elongation in the northeast-southwest direction and underwent a transformation towards a more north-south orientation. Moreover, the area encompassed by the ellipse decreased, indicating a more condensed and concentrated distribution of amoebic dysentery cases. Figure 16 the results of mean center and standard deviational ellipse of amoebic dysentery.

Hepatitis A

The mean center of hepatitis A initially shifted towards the northwest and subsequently returned to the southeast, ultimately locating in Gansu province. Notably, the major axes of the ellipse exhibited an elongation, indicating a more distinct northwest-southeast difference in the distribution of hepatitis A. Figure 17 The results of mean center and standard deviational ellipse of hepatitis A.

Hepatitis E

The mean center of hepatitis E initially resided in Shandong province before gradually shifting southwestward and ultimately settling in Hubei province. Concurrently, the ellipse representing its distribution transformed from an apparent northeast-southwest elongation to a more circular shape. Furthermore, the minor axes of the ellipse became longer, indicating a more dispersed and expanded distribution of hepatitis E. Figure 18 the results of mean center and standard deviational ellipse of hepatitis E.

Hand, Foot, and Mouth Disease (HFMD)

The mean center of HFMD exhibited a southwestward movement from Shandong province to Hunan province. Simultaneously, the shape of the ellipse transformed from a northwest-southeast elongation to a northeast-southwest elongation. This change in the shape of the ellipse signifies a shift in the difference of HFMD's distribution pattern. Figure 19 the results of mean center and standard deviational ellipse of hand, foot, and mouth disease.

Other infectious intestinal diseases

The mean center of the OIIDs (Other Intestinal Infectious Diseases) displayed a southwestward movement and remained primarily concentrated within Henan province. Although there was a slight change in the elongation direction of the ellipse, the overall shape of the ellipse was predominantly circular. This suggests that the directional characteristics of the OIIDs' distribution were not prominent. Figure 20 the results of mean center and standard deviational ellipse of other infecitous intestinal diseases.

Exploration of influential factors

Table 2 presents the VIF results, demonstrating that all variables had VIF values below 10. As the result indicated the absence of concerning multicollinearity, we proceeded to include all the candidate variables in our model.

Table 2 Multicollinearity evaluation results

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Table 3 and Fig 21 show the estimated Relative Risk (RR) and 95% confidence intervals (CIs) based on the spatial-temporal interactive model. Since we have standardized all the variables before fitting the model, the interpretation of RR will be expressed based on one-Standard Deviation (SD) increase in the standardized covariates.

Table 3 The estimated RR (95% CIs) for influential factors of different intestinal infections

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The cholera incidence would increase by 73% for a 26.84% increase in ARHST. The typhoid fever incidence would increase by 182% for a 5.35℃ increase in temperature and by 52% for a 536.99 increase in precipitation. The typhoid fever incidence would decrease by 34% for a 26.84% increase in ARHST and by 35% for a 9.6% increase in humidity. The paratyphoid fever incidence would increase by 179% for a 5.35℃ increase in temperature. The paratyphoid fever incidence would decrease by 29%, 18%, and 19% for every SD increase in ARHST, GDP, and wind speed respectively. Bacillary dysentery would increase by 32% for a 26.84% increase in ARHST. The bacillary dysentery incidence would decrease by 23%, 28%, and 28% for every SD increase in GDP, precipitation, and wind speed. The amoebic dysentery incidence would increase by 64% for a 9.6% increase in humidity while decreasing by 23% for every SD increase wind speed. The hepatitis A incidence would decrease by 16%, 29%, and 18% for every SD increase in GDP, humidity, and wind speed. The hepatitis E incidence would increase by 148% for one SD increase in GDP. The HMFD incidence would increase by 34% for every SD increase in temperature. The OIIDs would increase by 88% for a 26.84% increase in ARHST while decreasing by 46% and 18% for every SD increase in humidity and wind speed.

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