World Hepatitis Day will be observed Friday, July 28, which makes this a good time to learn more about three types of hepatitis and the risk factors for each.

Hepatitis is inflammation of the liver. The five main strains of the hepatitis virus are referred to as types A, B, C, D and E. While they all cause liver disease, they differ in geographic prevalence, modes of transmission, severity of illness and prevention methods, according to the World Health Organization.

In the U.S., the most common types of hepatitis are hepatitis A, hepatitis B and hepatitis C.

Hepatitis A

Hepatitis A is highly contagious, spreading through contact with contaminated food or water, or from close contact with an infected person or object. Unlike other types of viral hepatitis, hepatitis A does not cause long-term liver damage, and it doesn't become chronic.

In rare cases, hepatitis A can cause a sudden loss of liver function, especially in older adults or people with chronic liver diseases. Acute liver failure requires a stay in the hospital for monitoring and treatment. Some people with acute liver failure may need a liver transplant.

Mild cases of hepatitis A don't require treatment, and most people who are infected recover completely with no permanent liver damage. Practicing good hygiene, including frequent hand-washing, is one of the best ways to protect against hepatitis A.

You're at increased risk of hepatitis A if you:

• Travel or work in areas of the world where hepatitis A is common.
• Live with another person who has hepatitis A.
• Are a man who has sexual contact with other men.
• Have any type of sexual contact with someone who has hepatitis A.
• Are HIV positive.
• Are homeless.
• Use any type of recreational drugs, not just those that are injected.

The hepatitis A vaccine can prevent infection with the virus. If you're concerned about your risk of hepatitis A, ask your health care professional if you should be vaccinated.

Hepatitis B

Hepatitis B is passed from person to person through blood, semen or other bodily fluids. It does not spread by sneezing or coughing.

For most people, hepatitis B is short term, also called acute, and lasts less than six months. For others, hepatitis B infection becomes chronic, which increases their risk of developing liver failure, liver cancer or cirrhosis. The younger people are when they get hepatitis B, particularly newborns or children younger than 5, the higher the risk of the infection becoming chronic.

Chronic infection may go undetected for decades until a person becomes seriously ill from liver disease. A vaccine can prevent hepatitis B, but there's no cure if you have the condition.

Your risk of hepatitis B infection increases if you:

• Have unprotected sex with multiple sex partners or with someone who's infected with hepatitis B virus (HBV).
• Share needles during IV drug use.
• Are a man who has sex with other men.
• Live with someone who has a chronic HBV infection.
• Are an infant born to an infected mother.
• Have a job that exposes you to human blood.
• Travel to regions with high infection rates of HBV, such as Asia, the Pacific Islands, Africa and Eastern Europe.

Hepatitis B is a common reason for liver transplants in the U.S.

Hepatitis C

Hepatitis C is transmitted primarily by contaminated blood, and it also is a common reason for liver transplants in the U.S. Hepatitis C usually can be cured with oral medications taken every day for two to six months. But many people don't know they're infected because they have no symptoms, which can take decades to appear.

Hepatitis C infection that continues over many years can cause significant complications, including cirrhosis, liver cancer and liver failure. The U.S. Preventive Services Task Force recommends that all adults ages 18 to 79 be screened for hepatitis C, even those without symptoms or known liver disease. The largest group at risk includes everyone born between 1945 and 1965 — a population five times more likely to be infected than those born in other years.

Your risk of hepatitis C infection is increased if you:

• Are a health care worker who has been exposed to infected blood, which may happen if an infected needle pierces your skin.
• Have ever injected or inhaled illicit drugs.
• Have HIV.
• Received a piercing or tattoo in an unclean environment using unsterile equipment.
• Received a blood transfusion or organ transplant before 1992.
• Received clotting factor concentrates before 1987.
• Received hemodialysis treatments for a long period of time.
• Were born to a woman with a hepatitis C infection.
• Were ever in prison.
• Were born between 1945 and 1965, the age group with the highest incidence of hepatitis C infection.

Connect with others talking about hepatitis and liver failure in the Transplants Support Group on Mayo Clinic Connect, an online patient community moderated by Mayo Clinic.

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