Infected children have little to no apparent clinical illness, in contrast to adults in whom greater than 80% are symptomatic if infected. Infection rates are highest in low resource countries with inadequate public sanitation and large concentrated populations. In such regions, as much as 90% of children younger than 10 years old have been infected and are immune, corresponding both to lower rates of clinically symptomatic disease and outbreaks. The availability of a childhood vaccine has significantly reduced infections in the United States, with incidence declining by more than 95% as of 2013. Paradoxically, the highest rates of new infection now occur in young adults and adults who present with worse clinical illness. Specific populations at greatest risk include: travelers to endemic regions, men who have sex with men, those with occupational exposure to non-human primates, people with clotting disorders who have received clotting factors, people with history of chronic liver disease in whom co-infection with hepatitis A can lead to fulminant hepatitis, and intravenous drug users (rare). Hepatitis B
Hepatitis B is the most common cause of viral hepatitis in the world with more than 240 million chronic carriers of the virus, 1 million of whom are in the United States. In approximately two-thirds of patients who develop acute hepatitis B infection, no identifiable exposure is evident. Of those acutely infected, 25% become lifetime carriers of the virus.
Entecavir is safe, well tolerated, less prone to developing resistance, and the most potent of the existing hepatitis B antivirals; it is thus a first-line treatment choice. It is not recommended for lamivudine-resistant patients or as monotherapy in patients who are HIV positive. Telbivudine is effective but not recommended as first-line treatment; as compared to entecavir, it is both less potent and more resistance prone. Tenofovir is a nucleotide analogue and an antiretroviral drug that is also used to treat HIV infection. It is preferred to adefovir both in lamivudine-resistant patients and as initial treatment since it is both more potent and less likely to develop resistance.First-line treatments currently used include PEG IFN, entecavir, and tenofovir, subject to patient and physician preference. Treatment initiation is guided by recommendations issued by The American Association for the Study of Liver Diseases (AASLD) and the European Association for the Study of the Liver (EASL) and is based on detectable viral levels, HBeAg positive or negative status, ALT levels, and in certain cases, family history of HCC and liver biopsy. In patients with compensated cirrhosis, treatment is recommended regardless of HBeAg status or ALT level, but recommendations differ regarding HBV DNA levels; AASLD recommends treating at DNA levels detectable above 2x103 IU/mL; EASL and WHO recommend treating when HBV DNA levels are detectable at any level. In patients with decompensated cirrhosis, treatment and evaluation for liver transplantation are recommended in all cases if HBV DNA is detectable.