The most efficient route of hepatitis B transmission is
Answer: C
Direct blood-to-blood exposure through a needlestick or shared injecting equipment carries the highest risk, with mucosal and non-intact skin exposure to blood, semen and other fluids also effective. Childbirth and sexual contact are the other major routes.
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The average incubation period of hepatitis B to the onset of symptoms is about
Answer: D
Symptoms appear on average about 90 days after exposure, with a range of 60 to 150 days, and abnormal liver enzymes somewhat earlier at around 60 days. The long and variable interval often makes the source of infection impossible to identify.
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Hepatitis B virus remains infectious on environmental surfaces for at least
Answer: A
A week of survival outside the body means that blood-contaminated surfaces and shared items such as razors and toothbrushes are genuine routes of transmission. It is one reason the virus spreads within households without any sexual or injecting exposure.
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The proportion of infants infected with hepatitis B at birth who become chronically infected is about
Answer: B
An immature immune system fails to clear the virus, so about nine in ten infected newborns become chronic carriers, compared with about 30 per cent of children infected between one and five years. That gradient is precisely why vaccination begins at birth.
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The proportion of adults infected with hepatitis B who recover completely is about
Answer: C
Most adults mount an effective response and clear the virus, leaving lifelong immunity, so chronic infection in an adult is the exception. The risk of chronicity runs in the opposite direction to age, being highest in the newborn.
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Chronic hepatitis B infection leads to chronic liver disease in about
Answer: D
Between one in seven and one in four of those chronically infected develop cirrhosis, liver failure or liver cancer, which is why carriers need long-term monitoring. The remainder may carry the virus for decades without serious liver injury.
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The presence of hepatitis B surface antigen in serum indicates
Answer: A
The surface antigen is a viral product, so finding it means virus is present; whether the infection is acute or chronic is settled by other markers and by how long it persists. Antigen lasting beyond six months defines chronic infection.
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Antibody to hepatitis B surface antigen in the absence of any other marker indicates
Answer: B
The vaccine contains only the surface antigen, so it raises anti-HBs alone. Recovery from natural infection leaves anti-HBs together with antibody to the core antigen, and that core antibody is the marker that separates the two.
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Which marker distinguishes immunity from natural infection from immunity from vaccination?
Answer: C
Correct answer: Antibody to the core antigen
The vaccine contains only the surface antigen, so it raises antibody to that and to nothing else. Natural infection exposes the immune system to the whole virus, including the core, so anti-HBc is present. Its presence therefore marks past infection, and its absence in a person with surface antibody marks vaccination.
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IgM antibody to the hepatitis B core antigen indicates
Answer: D
Correct answer: recent or acute infection
IgM is the first class of antibody made and it wanes over a few months, so IgM anti-HBc points to infection within roughly the last six months. IgG anti-HBc persists for life and shows only that infection occurred at some time, which is why the two classes must be distinguished.
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