Cause

Hepatitis A is caused by a virus (hepatitis A virus, or HAV) that multiplies in liver cells and is shed in stool.

How HAV is spread

Hepatitis A virus is found in the stool (feces) of a person who has hepatitis A. The virus is spread most commonly when people put food or objects contaminated with stool containing HAV into their mouths.

Large numbers of people get the virus after drinking contaminated water because, in many parts of the world, drinking water is contaminated with raw sewage. The virus also may be spread by eating uncooked food (such as raw shellfish) and unpeeled fruits and vegetables washed in contaminated water. Hepatitis A outbreaks caused by contaminated drinking water are rare in the United States because water supplies are treated to destroy the virus and other harmful organisms.

In the U.S., HAV is spread mainly among people who have close contact with someone who has the virus. You can become infected with HAV if you:

• Eat food prepared by someone who does not wash his or her hands well after using the bathroom or changing a diaper.
• Don't wash your hands after changing a diaper.
• Eat raw or undercooked shellfish that was harvested from waters contaminated with raw sewage.
• Are a man and have sex with men.

Outbreaks of hepatitis A among children in day care facilities occur because children, especially those who wear diapers, may get stool on their hands and then touch objects that other children put into their mouths. Caregivers in day care centers can spread the virus if they do not wash their hands thoroughly after changing a child's diaper.

It is very rare for hepatitis A virus to be spread by infected blood or blood products. It is not known to be spread through saliva or urine.

Some people fear that hepatitis A infection is related to or increases the risk of contracting acquired immunodeficiency syndrome (AIDS). This is not true. The hepatitis A virus is not related to the human immunodeficiency virus (HIV), which causes AIDS, nor does it increase your risk of HIV infection. A person can be infected with both hepatitis A and HIV, but the two infections have nothing to do with each other.

Incubation and contagious periods

After the hepatitis A virus enters your body, the amount of virus grows for 2 to 7 weeks. The average incubation period is about 4 weeks.

Your stools and body fluids contain the highest levels of the virus 2 weeks before symptoms start. This is the time when you are most contagious, but you still may spread the virus after symptoms appear.