en Infectious Disease Infectious Disease Original Research Original Research <span style="font-size:13pt"><span style="text-justify:kashida"><span style="text-kashida:0%"><span style="text-autospace:none"><span new="" roman="" style="font-family:" times=""><span style="font-style:italic"><b>&nbsp;&nbsp;</b><b><span style="font-size:9.0pt"><span style="font-style:normal">&nbsp; Background: </span></span></b><span style="font-size:9.0pt"><span style="font-style:normal">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.</span></span></span></span></span></span></span></span><br> <span style="font-size:13pt"><span style="text-justify:kashida"><span style="text-kashida:0%"><span style="text-autospace:none"><span new="" roman="" style="font-family:" times=""><span style="font-style:italic"><span style="font-size:9.0pt"><span style="font-style:normal">&nbsp;&nbsp; <b>Methods:</b> 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&rsquo;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&rsquo;s I (Cluster and Outlier Analysis) in ArcGIS 10.4. Temporal trends were evaluated using deseasonalized time-series analysis.</span></span></span></span></span></span></span></span><br> <span style="font-size:13pt"><span style="text-justify:kashida"><span style="text-kashida:0%"><span style="text-autospace:none"><span new="" roman="" style="font-family:" times=""><span style="font-style:italic"><span style="font-size:9.0pt"><span style="font-style:normal">&nbsp;&nbsp; <b>Results:</b> 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&rsquo;s I test identified several &ldquo;High-Low&rdquo; outliers, indicating isolated local outbreaks within low-risk regions.</span></span></span></span></span></span></span></span><br> <span style="font-size:13pt"><span style="text-justify:kashida"><span style="text-kashida:0%"><span style="text-autospace:none"><span new="" roman="" style="font-family:" times=""><span style="font-style:italic"><span style="font-size:9.0pt"><span style="font-style:normal">&nbsp;&nbsp; <b>Conclusion:</b> 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.</span></span></span></span></span></span></span></span><br> &nbsp; Bloody Diarrhea, Time Series, Spatio-Temporal Analysis, Cluster Analysis, Iran 515 525 http://mjiri.iums.ac.ir/browse.php?a_code=A-10-10091-1&slc_lang=en&sid=1 Dariush Bastam bastam.da@iums.ac.ir 200319475328460098314 200319475328460098314 No Department of Epidemiology, School of Public Health, Iran University of Medical Sciences, Tehran, Iran Manoochehr Karami man.karami@yahoo.com 200319475328460098315 200319475328460098315 No Pandemic and Epidemic Preparedness and Response Research Network, Research Institute for Health Sciences and Environment, Shahid Beheshti University of Medical Sciences, Tehran, Iran Mahshid Nasehi nasehi.m@iums.ac.ir 200319475328460098316 200319475328460098316 No Department of Epidemiology, School of Public Health, Iran University of Medical Sciences, Tehran, Iran Masoud Salehi salehi74@yahoo.com 200319475328460098317 200319475328460098317 No Department of Biostatistics, School of Public Health, Iran University of Medical Sciences, Tehran, Iran Alireza Amouzandeh Nobaveh amouzandeh941.aa@gmail.com 200319475328460098318 200319475328460098318 No Department of Infectious Diseases, School of Medicine, Firoozabadi Hospital, Iran University of Medical Sciences, Tehran, Iran Mohammad Zeinali mzeinali411@gmail.com 200319475328460098319 200319475328460098319 No Head of National Department of Zoonotic Disease Control, Center for Communicable Diseases Control, Ministry of Health and Medical Education, Tehran, Iran Babak Eshrati eshrati.b@iums.ac.ir 200319475328460098320 200319475328460098320 No Department of Community and Family Medicine, School of Medicine, Iran University of Medical Sciences, Tehran, Iran