Causes and Risk Factors for Hepatitis B and HBV Infection
Risk factors for HBV transmission or the progression of HBV disease include:
Gender. Chronic hepatitis B progresses more rapidly in males than females; cirrhosis and HCC predominate in men and postmenopausal women (Shimizu 2007; El-Serag 2012). High serum levels of testosterone have been associated with increased HCC risk in HBV carriers (Yuan 1995). Additionally, among 42 men who underwent liver resection for HCC between 1995 and 1999, those whose preoperative testosterone levels were in the upper half of the distribution had greater disease recurrence and poorer survival rates over 5-year follow up (Lin 2007). In contrast, premenopausal women have lower liver iron stores and reduced production of pro-inflammatory cytokines, both reducing risk of liver disease; this also suggests a potential protective role of estrogens (Shimizu 2007).
HIV infection. An estimated 10% of the 40 million people infected with HIV worldwide are also infected with HBV. HIV infection significantly increases the risk of developing cirrhosis and HCC in individuals carrying both viruses (WHO 2009), and HBV increases the rate of mortality in HIV patients on antiretroviral therapy (Nikolopoulos 2009).
Alcohol use. A few studies investigating the association between alcohol intake, HBV infection, and the progression of liver disease found a 1.2 to 3 times increased risk of HCC among heavy alcohol users (El-Serag 2012).
Sexual behavior. Hepatitis B is considered a sexually transmitted disease (STD), and in areas with low HBV incidence such as the U.S., sexual transmission represents a major route of infection. While homosexual men have the highest risk of infection (70% infected after 5 years of activity), heterosexual transmission has been increasing in frequency. In heterosexuals, multiple or high-risk partners (such as HBV carriers or illicit IV drug users), history of STD, and long duration of sexual activity all increase risk of transmission (Hou 2005).
Intravenous (IV) illicit drug use. Injection of illicit IV drugs is a major route of HBV infection in areas of low HBV incidence. In the U.S. and Western Europe, 23% of hepatitis B patients were infected by needles (Hou 2005).
Contact with infected fluids. Individuals in frequent contact with potentially contaminated blood products or bodily fluids (eg, health care workers, lab technicians, police, firefighters, and patients requiring frequent transfusions or hemodialysis) are at increased risk of HBV infection. Contaminated instruments (eg, those used for surgery, body piercing, acupuncture, or tattooing) also represent possible sources of infection (Hou 2005).
Parent-to-child transfer. As mentioned earlier, mother-to-child transfer is a significant source of viral transmission in both high-prevalence and low-prevalence geographic areas. In contrast to transmission by sexual contact, drug use, or contact with infected blood (which all have a <5% risk of chronic infectivity), infection at birth carries a 90% risk of chronicity (Nebbia 2012; Hou 2005).