Hepatitis A Chronic Immunity in Iran: A Geographic Information System-Based Study

Background: Chronic immunity to hepatitis A (HA) is largely influenced by environmental factors, such as socioeconomic indicators, public health conditions, and access to safe water. In the past two decades, Iran has witnessed improvements in socioeconomic status, increased urbanization, enhanced health education, improved access to safe drinking water sources, and better public health conditions. However, these changes have not been uniform across all regions of Iran, and varying epidemiological situations are expected. Objectives: This study aimed to delineate the pattern of HA chronic immunity across different regions of Iran using geographical information system (GIS) mapping. Methods: The study included a total of 3255 individuals who tested positive for anti-hepatitis A virus (anti-HAV) immunoglobulin G (IgG). This study analyzed factors such as place of residence, marital status, age, and gender to explore possible relationships. Univariate and multivariable analyses were conducted to identify independently associated factors for HA. A locally weighted scatterplot smoothing (LOWESS) multivariate model was developed using a backward stepwise approach. Geographical variations in the prevalence of HA chronic immunity in the general population of Iran were assessed to understand spatial effects and risk factors. A Bayesian spatial model was employed to identify the spatial pattern of HA chronic immunity prevalence, using OpenBUGS version 3.2.3. Results: The prevalence of HAV immunity was higher in regions with mild semi-dry climates (aPR = 2.37, 95% confidence interval [CI] = 2.30 - 3.33, P< 0.001), medium semi-dry climates (aPR = 1.37, 95% CI = 1.14 - 1.63, P< 0.001), dry climates (aPR = 1.13, 95% CI = 0.9 - 1.4), and ultra-dry climates (aPR = 1.79, 95% CI = 1.05 - 2.98, P = 0.033), compared to semi-humid climates. Other variables did not exhibit a significant relationship with HA chronic immunity. The GIS analysis map revealed that immunity to HA was generally lower in the capital cities of Iran’s provinces. However, most central regions of Iran exhibit medium endemicity; nevertheless, higher immunity to HA was observed in border areas and coastal regions, particularly in the northern part of the country. Conclusions: Different regions of Iran display distinct patterns of HAV endemicity, influenced by the country’s climatic diversity.