A sexually transmitted infection (STI) is an infection that is passed from one person to another during sexual contact. Chlamydia is an STI caused by bacteria. Many people with chlamydia have no symptoms, so they can pass it on without knowing. It can cause damage to the reproductive system. Because it is a bacterial infection, it can be treated with antibiotics.
HIV is an STI caused by a virus. It is spread by sexual contact, by sharing needles, and from a mother to her baby. HIV destroys white blood cells, so the immune system gets weaker and the person can develop AIDS. Antibiotics do not work on viruses, so HIV cannot be cured with them, although other drugs can control it.
The spread of both infections can be reduced. Using a condom during sex acts as a barrier between partners. Regular screening finds infections early, and partners can be treated. Not sharing needles reduces the spread of HIV.