Infection with hepatitis B occult (OBI) is characterized by absence of hepatitis B surface antigen (HBsAg) in commercial immunoassays, despite the persintência HBV DNA in the serum and / or liver tissue. The few studies of this clinical form in Brazil, mainly in the Amazon region, seen as an endemic area for hepatitis B virus (HBV), hamper the analysis to identify the epidemiological profile of the site. The objective of study was to determine the prevalence of hepatitis B occult in patients attended at the Tropical Medicine Center outpatient - Federal University of Pará, from January 2011 to December 2015, characterization of circulating viral genotypes and identify the main risk factors for the acquisition of this clinical form. Four hundred and sixty-five serum samples were submitted to ELISA (Enzyme-linked immunosorbent assay) for detection of serological markers of HBV (HBsAg, anti-HBc and anti-HBs). Total 181 patients resulted in a non-reactive HBsAg, anti-HBc reactive and anti-HBs nonreactive. These were screened with a PCR assay for identification of HBV-DNA. Subsequently, the positive samples were sequenced to identify the genotypes and mutations. Of the 181 samples, 26 (14,36%) had serum HBV-DNA, demonstrating the infection by OBI. The average age of 39 years, 53.45% (14/26) were married and 50% (13/26) were male. The genotype A was found in 88.46% (23/26), with the most prevalent subgenotype A1 with 78.26% (18/23) and genotype A2 with 21.73% (5/23). The genotype F was found in only 11.53% (3/26), in the presence of F2 genotype in all samples. As for risk factors only the nail pliers share was statistically significant. Some amino acid substitutions were identified in samples of patients with HBO compared with the HBsAg samples reagentes, but no mutation was identified. The study found a high prevalence of hepatitis B occult in patients treated at the Tropical Medicine Center – UFPA. HBV molecular studies are of fundamental importance for the identification of patients who are considered healthy, but they do have the infection and can be a transmitter disease potential.
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