Symptoms may not show up until 1 to 6 months after you catch the virus. You may not feel anything, and about a third of the people with this disease don’t. They only find out through a blood test.

To help keep a hepatitis B infection from spreading:

The number of people who get this disease is down, the CDC says. Rates have dropped from an average of 200,000 per year in the 1980s to around 18,000 in 2012. People between the ages of 20 and 49 are most likely to get it.

Only 5% to 10% of adults and children older than 5 who have hepatitis B end up with a chronic infection. The numbers aren’t so good for those younger than 5 (25% to 50%) and even higher for infants infected at birth (90%).

As many as 1.4 million people in the U.S. are carriers of the virus.

HIV stands for human immunodeficiency virus. It is the virus that can lead to acquired immunodeficiency syndrome, or AIDS, if not treated. Unlike some other viruses, the human body can’t get rid of HIV completely, even with treatment. So once you get HIV, you have it for life.

HIV is spread mostly through four body fluids:

These symptoms can last anywhere from a few days to several weeks. During this time, HIV infection may not show up on some types of HIV tests, but people who have it are highly infectious and can spread the infection to others.