Spatio-Temporal Dynamics of Bloody Diarrhea Syndrome in Iran: A County-Level Identification of Clusters, Hot Spots, Outliers, and Seasonal Trends (2015-2019).

Abstract

Background: Bloody diarrhea remains a significant public health challenge in developing countries. Despite general improvements in health indicators, Iran continues to experience geographical disparities in the incidence of foodborne and waterborne diseases. This study aimed to analyze spatiotemporal patterns, identify high-risk clusters, and detect local outliers of bloody diarrhea across all counties in Iran over a five-year period.

Methods: This retrospective ecological study was conducted using data from the National Surveillance System on 62,787 confirmed cases of bloody diarrhea from 2015 to 2019. The unit of analysis was the county level. The Global Moran's I index was employed to test for spatial autocorrelation. Local spatial patterns were examined using the Getis-Ord Gi* statistic (Hot Spot Analysis) and Anselin Local Moran's I (Cluster and Outlier Analysis) in ArcGIS 10.4. Temporal trends were evaluated using deseasonalized time-series analysis.

Results: The overall incidence rate showed a mild downward trend with a distinct seasonal peak in May (mid-spring). The disease predominantly affected children under 9 years of age (51.3%) and males (54.1%). Global spatial analysis confirmed significant clustering in all years except 2016. Hot spot analysis revealed a geographical shift in high-risk areas: while intense but transient clusters were identified in central Iran (Isfahan and Chaharmahal and Bakhtiari) only in 2015 (coinciding with a major outbreak), persistent high-risk clusters were established in the southeastern and eastern provinces from 2017 to 2019. Notably, the Anselin Local Moran's I test identified several "High-Low" outliers, indicating isolated local outbreaks within low-risk regions.

Conclusion: The epidemiology of bloody diarrhea in Iran is characterized by a dual pattern: transient epidemic outbreaks in central/tourist regions and chronic endemicity in underdeveloped southeastern border areas. The findings indicate a spatial transition of the disease burden toward the southeast. Effective control strategies should prioritize infrastructure development in the endemic eastern belt and the implementation of targeted syndromic surveillance in identified outlier hot spots to manage seasonal outbreaks.