Wallach's Interpretation of Diagnostic Tests: Pathways to Arriving at a Clinical Diagnosis (183 page)

   Anti-HEV-IgG positive: Remote infection.

   Recent travel to an endemic area should be documented (e.g., Mexico, India, Africa, or Russia).

   Hepatitis Viruses Transmitted by Blood-Borne Routes (HBV, HCV, and HDV)

HBV, HCV, and HDV are most commonly transmitted by exposure to blood, semen, or infected body fluids. Infection may also be transmitted by perinatal/ vertical (especially in HBV in areas with high endemic rate) and sexual routes (now the most common exposure for HBV infection). Transmission by transfusion or transplantation has fallen as a result of screening.

   
HBV
(see Figure
5-7
)

   HBV is a double-stranded DNA
Hepadnavirus
. HBV infection occurs worldwide.

   In a 2010 CDC survey, only 36% of patients with acute HBV infection reported any high-risk behavior or known exposure in the 6 months prior to illness. Specific high-risk behaviors or exposure risks include employment in health care settings involving contact with blood or potential needle-stick injury, dialysis or kidney transplant, transfusion of blood products, recent surgery, injection drug use, high-risk sexual practices, or close contact with any person at high risk for HBV infection. The case fatality rate for acute HBV infection is approximately 1.5% (1.1 case/100,000 population). It is highest in patients 30–39 years of age.

   Symptoms and disease: Symptomatic disease occurs in a minority of patients with acute HBV infection (<1 year old: <1%; 1–5 years old: 5–15%; >5 years old: 30–50%). Symptoms and evidence of active infection occurs approximately 2–3 months (range 2 to 5 months) after exposure. HBsAg, anti-HBc IgM, and HBeAg appear late in the prodromal phase. In patients who recover without progression to chronic infection, the titer of these markers, as well as the ALT, begin to fall during the phase of active disease, usually returning to normal within 4 to 6 months. Most patients with acute HBV infection recover completely. The risk of chronic infection depends on the age of acquisition of HBV infection (>90% of infants; 25–50% of children aged 1 to 5 years; 6–10% of older children and adults).

   
HBV Diagnosis and Laboratory Testing

A number of laboratory tests are used to different stages of HBV infection:

   Hepatitis B surface antigen (
HBsAg
) is the earliest indicator of active HBV infection. HBsAg is usually detectable within 27–41 days (as early as 14 days) of the onset of infection. HBsAg appears 7–26 days before transaminase abnormalities and peaks as ALT rises. HBsAg detection persists during the acute illness. HBsAg usually disappears 12–20 weeks after onset of symptoms in uncomplicated HBV infection.

   Detection of HBsAg for >6 months defines chronic infection or a chronic carrier state. Hepatitis B vaccination does not cause a positive HBsAg. HBsAg titers are not of clinical value and may never be detected in some patients; diagnosis of acute HBV infection is based on detection of HBc-IgM.

   Antibody to HBsAg (
anti-HBs
), without detectable HBsAg, indicates recovery from HBV infection, absence of infectivity, and immunity from future HBV infection. Anti-HBs may be seen after transfusion due to passive transfer. Anti-HBs is found in 80% of patients after clinical cure. The appearance of anti-HBs may take several weeks or months after HBsAg has disappeared and ALT has returned to normal, causing a 2- to 6-week “window” period.