The changing epidemiology of delta hepatitis in Türkiye over three decades: A systematic review

Hepatitis D virus (HDV) infection represents the most serious form of chronic hepatitis. Turkey is among the countries with high HDV and intermediate hepatitis B virus prevalence. In Turkey, hepatitis B virus (HBV) vaccine series was included in the routine vaccination program in 1998. There have been regional differences in prevalence of HBV and HDV. Although a decline in HDV prevalence is estimated, there are uncertainties about the epidemic patterns of it. HDV prevalence was studied in varying groups and geographic regions. In this study, we aimed to analyse hepatitis D epidemiology in all groups and geographic regions in recent 35 years. During the study period of 35 years, 111 publications were noted. The analysis was done on the basis of three periods: 1999 and before (Period 1), 2000-2009 (Period 2), and 2010 and after (Period 3). The groups studied included inactive carrier state, chronic hepatitis B, all HBsAg-positive individuals and special groups. Among inactive HBV carriers, HDV prevalence did not change significantly over three decades. Among patients with chronic hepatitis, studies reported decreasing (from Period 1 to Period 2) and then increasing (from Period 2 to period 3) HDV prevalence. The studies including all HBsAg-positive patients reported decreasing (from Period 1 to Period 2) and then increasing (from Period 2 to period 3) HDV prevalence. Cumulative data of these 3 groups were taken to reveal HDV prevalence in HBV-infected patients, and it showed decreasing (from Period 1 to Period 2) and then increasing (from Period 2 to period 3) HDV prevalence. Cumulative data of these 3 groups analysed according to the geographic regions of the country showed that Eastern and Southeastern Anatolia regions still have a high burden of HDV. The study showed that although HDV prevalence decreased from 8.3% in Period 1 to 4.8% in Period 2, it tended to increase 5.5% in Period 3. HDV infection is still a healthcare problem in Turkey.