BACKGROUND: Updates on the incidence of and risk factors for acute hepatitis delta virus infection in Italy, as well as in other countries, are lacking, and the impact of the mandatory anti-hepatitis B vaccination has not been evaluated. METHODS: We performed a case-control study within a population-based surveillance for acute viral hepatitis. RESULTS: During 1993-2004, 344 cases of acute hepatitis delta virus infection were reported. After a peak in 1993 (2.8 cases per 1 million population), the incidence decreased from 1.7 to 0.5 cases per 1 million population. Coinfections were prevalent. The decrease in incidence particularly affected young adults, and it paralleled the decrease in incidence of acute hepatitis B. In 1993, being an injection drug user (adjusted odds ratio [OR(adj)], 67.9; 95% confidence interval [CI], 18.1-254.5) or being a member of a household with a carrier of hepatitis B surface antigen (OR(adj,) 14.8; 95% CI, 3.0-72.9) were the only independent predictors of infection. During 1994-2004, being an injection drug user (OR(adj), 36.8; 95% CI, 20.7-65.4), cohabitation with an injection drug user (OR(adj), 4.2, 95% CI, 1.7-12.3), hospitalization (OR(adj), 3.5; 95% CI, 1.9-6.6), receipt of dental therapy (OR(adj), 2.3; 95% CI, 1.4-3.6), promiscuous sexual activity (OR(adj), 2.2; 95% CI, 1.4-3.6), and receipt of beauty treatment (OR(adj), 2.0; 95% CI, 1.3-3.2) were independently associated with infection. CONCLUSIONS: Incidence of acute hepatitis delta infection is markedly decreasing in Italy. Undergoing invasive medical procedures, engaging in promiscuous sexual activity, and receiving beauty treatments are emerging, in addition to injection drug use, as important risk factors for infection. Further efforts are needed to increase vaccine coverage in high-risk groups and to implement the safety of invasive procedures performed both inside and outside health care facilities.
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