Over 350 million persons worldwide and 730,000 persons in the United States have chronic hepatitis B virus (HBV) infection, a major cause of cirrhosis and liver cancer [1,2]. Almost 20 years ago, the Alaska Native population has had one of the highest rates of chronic hepatitis B, and chronic liver disease was associated with higher proportion of deaths among American Indian/Alaska Native people compared to other racial/ethnic groups in the United States [3,4].

Three phases of chronic HBV infection are recognized: the immune tolerant phase, the immune active phase, and the inactive phase [5]. Although a high prevalence of reactivation of HBV infection has been documented among immunosuppressed individuals in the inactive hepatitis B phase [6], reactivation also might occur among non-immunosuppressed individuals. However, the proportion of persons in the inactive phase of chronic hepatitis B who will reactivate and the risk factors for reactivation are largely unknown [6]. Cohort studies assessing the incidence of and risk factors for hepatitis B reactivation among persons in the inactive phase of chronic hepatitis B are limited in number and the majority of studies recruited inactive carriers from hospitals [7,8], or blood banks [9,10]. Studies including population-based cohorts are lacking. Hence, it is unclear how frequently follow-up visits and testing should be performed among persons in the inactive hepatitis B phase. Current American Association for the Study of Liver Disease (AASLD) practice guidelines suggest that persons in the inactive phase should be followed every 6–12 months [11].

We conducted this study to determine the incidence of and identify factors associated with hepatitis B reactivation in a population-based cohort of Alaska Native persons in the inactive phase of chronic hepatitis B.

The mean age of study participants at the time of entry into the study was 40.1 ± 14.3 years; 43% were male. More than half were diagnosed with a positive HBsAg before the age of 20 years. The ALT levels were within normal range for all cohort members, and 13% had HBV DNA ≥ 1000 IU/mL at study entry (Table 1).

This cohort was followed up for an average of 7.4 ± 1.9 years (median: 8.2 years; range: 1.3–9.2 years), had a median of 10 (range: 1–83) ALT measurements (96.1% had three or more ALT and 84.1% had 5 or more ALT), and a median of 2 (range: 1–19) HBV DNA levels during the study period. A total of 36 (9%) inactive carriers developed reactivation of their HBV infection after an average of 5.8 ± 2.0 years (median: 6.7 years; range: 1.3–9.0 years) of follow-up. The first elevated median HBV DNA level among those who reactivated was 3701 IU/mL (range: 2040–65,933 IU/mL) and 25% of those who reactivated had HBV DNA ≥ 10,000 IU/mL on their first elevated HBV DNA. Peak median HBV DNA levels among those who reactivated was 4379 IU/mL (range: 2040–973,173 IU/mL) and 33% of those who reactivated had peak HBV DNA levels ≥10,000 IU/mL. Among the 36 carriers who reactivated their hepatitis B infection, 11 had a maximum ALT > 100, and 31 had at least one repeat HBV DNA level during the follow-up period. Of these, 19 (61%) had elevated HBV DNA on more than one occasion.

The annual incidence of reactivation of hepatitis B was 1.2% after 2984 person-years of follow-up (Table 2). The highest annual incidence rates of reactivation were found among inactive carriers who were ≥50 years old (1.8%) at study entry, however the incidence of reactivation was not statistically different across the various age groups (p = 0.06). The proportion of persons who had reactivation of infection increased with study time in both genders. However, a larger proportion of males had reactivation earlier during the study period (within 2–4 years) compared to females who generally experienced reactivation 6 years after study entry (Fig. 1).

In the unadjusted analysis, persons aged 40–49 years at study entry had a lower risk for reactivation of infection than those aged 18–29 years (Table 3). Males were two times more at risk of reactivation than females. Ethnic group and age at first detection of a positive HBsAg were not significant determinants of reactivation. Almost one in four inactive carriers of hepatitis B who had HBV DNA > 1000 IU/mL on study entry had reactivation, compared to only 4% of those with HBV DNA levels <29 IU/mL (Table 3). Furthermore, compared to inactive carriers having an HBV DNA < 1000 IU/mL at study entry, those with HBV DNA ≥ 1000 IU/mL had a significantly higher incidence of hepatitis B reactivation (32.5 per 1000 persons per year vs. 8.9 per 1000 persons per year, p < 0.01). Persons with HBV genotype B had a significantly higher cumulative incidence of reactivation (22%) compared to those with other HBV genotypes (9%).

Cox proportional hazards regression analysis showed that the risk of reactivation of hepatitis B was independently associated with age at study entry since persons aged 30–49 years at study entry had significantly lower risk for reactivation than those aged 18–29 years. In addition, male sex (Hazard Ratio (HR) = 2.41; 95% confidence interval (CI): 1.17–4.96), HBV DNA ≥ 1000 IU/mL at study entry (HR = 7.61; 95% CI: 2.81–20.6), and HBV genotype B (HR = 6.08; 95% CI: 1.32–28.0) were also significantly associated with reactivation of hepatitis B (Table 4). Of the 414 persons in the inactive phase of hepatitis B, 19 (4.6%) were treated for hepatitis B after entry into the study; of the 19, seven (36.8%) had reactivation of hepatitis B infection. Three were treated prior to reactivation because of elevated AFP (n = 1) or HCC (n = 2), and four were treated after reactivation; of these four, three had consistent elevations in HBV DNA after treatment (two of them had cancer: gastric cancer, colon cancer); the remaining 12 patients who did not reactivate were treated because of a family history of HCC (n = 3), undergoing chemotherapy for another cancer (n = 2), HCC (n = 2), undergoing immunosuppressive treatment for Crohn’s disease (n = 2), chronic AFP elevation (n = 1), receiving immunosuppressive therapy for auto-immune hepatitis (n = 1), and presence of cirrhosis (n = 1).

Of the 378 persons who did not have reactivation of HBV infection, 136 (36.0%) experienced one or more ALT elevations with 30 (7.9%) persons having ALT ≥ 100 IU/L with no increase in HBV DNA ≥ 2000 IU/mL. In addition, 13 persons had an elevation of HBV DNA ≥ 2000 IU/mL (median: 3366 IU/mL, range: 2120–42,300 IU/mL) without ever having an ALT ≥ 40 IU/L. During 2001–2010, 26 (8.7%) inactive carriers of chronic hepatitis B seroconverted to a negative HBsAg for an annual rate of 8.7 sero-conversions per 1000 carriers and none had reactivation of hepatitis B during follow-up.

Of the 13 cohort members who had a liver biopsy during the study, two inactive carriers had minimal fibrosis (Ishak score = 1), and two other had mild fibrosis (Ishak score = 2), but none were diagnosed with cirrhosis. Four cohort members developed HCC within 2.7, 4.6, 6.2, and 7.6 years after study entry; however none met the criteria for reactivated hepatitis B infection and none had elevations in HBV DNA based on repeated testing. A total of 28 (6.8%) inactive carriers died during the study period with an annual mortality rate of 0.9%. One inactive carrier died from HCC, two from hepatic failure and one from liver failure secondary to cancer of the gallbladder.

This study measured the incidence of and assessed risk factors for hepatitis B reactivation in a cohort of 414 persons in the inactive phase of chronic hepatitis B in Alaska who were followed for an average of 7.4 years. The annual incidence of reactivation was 1.2% and a total of 9% experienced reactivation by the end of 2010. The prevalence and incidence of reactivation seem to vary by the duration of follow-up and the HBV DNA cut-off point considered for reactivation. Studies which followed persons in the inactive phase of chronic hepatitis B for less than 5 years, rarely reported occurrence of reactivation among inactive carriers although the majority had detectable low levels of HBV DNA [17,18]. Longitudinal studies with an average of 7–10 years of follow-up reported a cumulative incidence of reactivation ranging from 2.0% to 23.8% [7–9,19], and an annual incidence rate of reactivation ranging between 0.4% and 1.6% [9,19,20]. Some studies used an HBV DNA ≥ 2000 IU/mL (10⁴ copies/mL) to indicate reactivation of infection [9,19], while other studies defined reactivation of hepatitis B as HBV DNA ≥ 20,000 IU/mL (10⁵ copies/mL) [7,8] which would affect estimates of incidence rates.

In our study, males had a higher risk for and more importantly tended to experience reactivation of HBV infection sooner after entry into the study then females. Male sex has been previously reported as a risk factor for reactivation [7,9,21], which is consistent with increased risk of chronic HBV infection, liver cancer, and death among males compared to females with HBV infection [22].

The most important finding in this study was the high risk of reactivation in those with a baseline HBV DNA ≥ 1000 IU/mL, which occurred in one quarter of inactive carriers fitting this category. Inactive carriers with HBV DNA ≥ 1000 IU/mL had almost a fourfold higher incidence rate of reactivation than those with HBV DNA < 1000 IU/mL. The AASLD chronic hepatitis B practice guidelines recommend following chronically infected patients every 3–12 months depending on disease activity [11]. Our finding suggests the need to follow-up inactive carriers with HBV DNA ≥ 1000 IU/mL more frequently than others.

While we found a higher risk for reactivation among inactive carriers with genotype B infection, only few inactive carriers in our cohort had genotype B (n = 9) leading to a wide confidence interval. A higher likelihood of reactivation was reported among inactive carriers with genotype C infection compared to those with genotype B in Taiwan [21,23], while longitudinal studies in Europe included mainly homogeneous populations infected with genotype D. We had 23 inactive carriers with genotype C, therefore we can rule out that having a larger number of genotype C inactive carriers might have influenced the findings.

Although 9% of inactive carriers in our cohort experienced reactivation, very few developed advanced liver disease which is consistent with findings from several studies [7,8,10,19,20]. It is notable that none of the four inactive carriers who were diagnosed with HCC during the study had reactivation. However, these inactive carriers were treated as soon as HCC was diagnosed which might have been responsible for lowering their risk. Our findings reinforce the importance of regular surveillance for HCC among HBV infected persons who remain in the inactive phase.

This study has several limitations. Data on other risk factors that might potentially influence reactivation such as alcohol intake, smoking, diabetes status, and HBV precore and basal core mutations were unavailable. Moreover, biopsy results were lacking from a large proportion of the study population because most of these individuals live in remote villages making it impossible to examine them on a regular basis. We could not calculate the incidence of reactivation by the age at HBV infection, as the exact time of infection was not available for the majority of inactive carriers; however a large prospective study conducted in this population showed that most persons who became chronically infected with HBV infection were exposed to HBV at a very young age [24].

Despite these limitations, the findings in this study are of significant benefit and might help identify persons in the inactive phase of chronic hepatitis B who need closer follow-up. Although the incidence of reactivation is low after almost 10 years of follow-up, males, and persons having HBV DNA ≥ 1000 IU/mL might need more frequent follow-up, compared to others in the inactive phase. In addition those who experience reactivation might need to be treated sooner after reactivation in order to avoid complications of HBV infection such as cirrhosis and liver cancer.